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objtool: Implement stack validation 2.0

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This is a major rewrite of objtool.  Instead of only tracking frame
pointer changes, it now tracks all stack-related operations, including
all register saves/restores.

In addition to making stack validation more robust, this also paves the
way for undwarf generation.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Jiri Slaby <jslaby@suse.cz>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: live-patching@vger.kernel.org
Link: http://lkml.kernel.org/r/678bd94c0566c6129bcc376cddb259c4c5633004.1498659915.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Josh Poimboeuf 2017-06-28 10:11:07 -05:00 committed by Ingo Molnar
parent c207aee480
commit baa41469a7
11 changed files with 1133 additions and 323 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

159
tools/objtool/Documentation/stack-validation.txt
View File

@ -127,28 +127,13 @@ b) 100% reliable stack traces for DWARF enabled kernels
c) Higher live patching compatibility rate
(NOTE: This is not yet implemented)
Currently with CONFIG_LIVEPATCH there's a basic live patching
framework which is safe for roughly 85-90% of "security" fixes. But
patches can't have complex features like function dependency or
prototype changes, or data structure changes.
There's a strong need to support patches which have the more complex
features so that the patch compatibility rate for security fixes can
eventually approach something resembling 100%. To achieve that, a
"consistency model" is needed, which allows tasks to be safely
transitioned from an unpatched state to a patched state.
One of the key requirements of the currently proposed livepatch
consistency model [*] is that it needs to walk the stack of each
sleeping task to determine if it can be transitioned to the patched
state. If objtool can ensure that stack traces are reliable, this
consistency model can be used and the live patching compatibility
rate can be improved significantly.
[*] https://lkml.kernel.org/r/cover.1423499826.git.jpoimboe@redhat.com
Livepatch has an optional "consistency model", which is needed for
more complex patches. In order for the consistency model to work,
stack traces need to be reliable (or an unreliable condition needs to
be detectable). Objtool makes that possible.
For more details, see the livepatch documentation in the Linux kernel
source tree at Documentation/livepatch/livepatch.txt.
Rules
-----
@ -201,80 +186,84 @@ To achieve the validation, objtool enforces the following rules:
return normally.
Errors in .S files
------------------
Objtool warnings
----------------
If you're getting an error in a compiled .S file which you don't
understand, first make sure that the affected code follows the above
rules.
For asm files, if you're getting an error which doesn't make sense,
first make sure that the affected code follows the above rules.
For C files, the common culprits are inline asm statements and calls to
"noreturn" functions. See below for more details.
Another possible cause for errors in C code is if the Makefile removes
-fno-omit-frame-pointer or adds -fomit-frame-pointer to the gcc options.
Here are some examples of common warnings reported by objtool, what
they mean, and suggestions for how to fix them.
1. asm_file.o: warning: objtool: func()+0x128: call without frame pointer save/setup
1. file.o: warning: objtool: func()+0x128: call without frame pointer save/setup
The func() function made a function call without first saving and/or
updating the frame pointer.
updating the frame pointer, and CONFIG_FRAME_POINTER is enabled.
If func() is indeed a callable function, add proper frame pointer
logic using the FRAME_BEGIN and FRAME_END macros. Otherwise, remove
its ELF function annotation by changing ENDPROC to END.
If the error is for an asm file, and func() is indeed a callable
function, add proper frame pointer logic using the FRAME_BEGIN and
FRAME_END macros. Otherwise, if it's not a callable function, remove
its ELF function annotation by changing ENDPROC to END, and instead
use the manual CFI hint macros in asm/undwarf.h.
If you're getting this error in a .c file, see the "Errors in .c
files" section.
If it's a GCC-compiled .c file, the error may be because the function
uses an inline asm() statement which has a "call" instruction. An
asm() statement with a call instruction must declare the use of the
stack pointer in its output operand. For example, on x86_64:
register void *__sp asm("rsp");
asm volatile("call func" : "+r" (__sp));
Otherwise the stack frame may not get created before the call.
2. asm_file.o: warning: objtool: .text+0x53: return instruction outside of a callable function
2. file.o: warning: objtool: .text+0x53: unreachable instruction
A return instruction was detected, but objtool couldn't find a way
for a callable function to reach the instruction.
Objtool couldn't find a code path to reach the instruction.
If the return instruction is inside (or reachable from) a callable
function, the function needs to be annotated with the ENTRY/ENDPROC
macros.
If the error is for an asm file, and the instruction is inside (or
reachable from) a callable function, the function should be annotated
with the ENTRY/ENDPROC macros (ENDPROC is the important one).
Otherwise, the code should probably be annotated with the CFI hint
macros in asm/undwarf.h so objtool and the unwinder can know the
stack state associated with the code.
If you _really_ need a return instruction outside of a function, and
are 100% sure that it won't affect stack traces, you can tell
objtool to ignore it. See the "Adding exceptions" section below.
3. asm_file.o: warning: objtool: func()+0x9: function has unreachable instruction
The instruction lives inside of a callable function, but there's no
possible control flow path from the beginning of the function to the
instruction.
If the instruction is actually needed, and it's actually in a
callable function, ensure that its function is properly annotated
with ENTRY/ENDPROC.
If you're 100% sure the code won't affect stack traces, or if you're
a just a bad person, you can tell objtool to ignore it. See the
"Adding exceptions" section below.
If it's not actually in a callable function (e.g. kernel entry code),
change ENDPROC to END.
4. asm_file.o: warning: objtool: func(): can't find starting instruction
4. file.o: warning: objtool: func(): can't find starting instruction
or
asm_file.o: warning: objtool: func()+0x11dd: can't decode instruction
file.o: warning: objtool: func()+0x11dd: can't decode instruction
Did you put data in a text section? If so, that can confuse
Does the file have data in a text section? If so, that can confuse
objtool's instruction decoder. Move the data to a more appropriate
section like .data or .rodata.
5. asm_file.o: warning: objtool: func()+0x6: kernel entry/exit from callable instruction
5. file.o: warning: objtool: func()+0x6: unsupported instruction in callable function
This is a kernel entry/exit instruction like sysenter or sysret.
Such instructions aren't allowed in a callable function, and are most
likely part of the kernel entry code.
If the instruction isn't actually in a callable function, change
ENDPROC to END.
This is a kernel entry/exit instruction like sysenter or iret. Such
instructions aren't allowed in a callable function, and are most
likely part of the kernel entry code. They should usually not have
the callable function annotation (ENDPROC) and should always be
annotated with the CFI hint macros in asm/undwarf.h.
6. asm_file.o: warning: objtool: func()+0x26: sibling call from callable instruction with changed frame pointer
6. file.o: warning: objtool: func()+0x26: sibling call from callable instruction with modified stack frame
This is a dynamic jump or a jump to an undefined symbol. Stacktool
This is a dynamic jump or a jump to an undefined symbol. Objtool
assumed it's a sibling call and detected that the frame pointer
wasn't first restored to its original state.
@ -282,24 +271,28 @@ they mean, and suggestions for how to fix them.
destination code to the local file.
If the instruction is not actually in a callable function (e.g.
kernel entry code), change ENDPROC to END.
kernel entry code), change ENDPROC to END and annotate manually with
the CFI hint macros in asm/undwarf.h.
7. asm_file: warning: objtool: func()+0x5c: frame pointer state mismatch
7. file: warning: objtool: func()+0x5c: stack state mismatch
The instruction's frame pointer state is inconsistent, depending on
which execution path was taken to reach the instruction.
Make sure the function pushes and sets up the frame pointer (for
x86_64, this means rbp) at the beginning of the function and pops it
at the end of the function. Also make sure that no other code in the
function touches the frame pointer.
Make sure that, when CONFIG_FRAME_POINTER is enabled, the function
pushes and sets up the frame pointer (for x86_64, this means rbp) at
the beginning of the function and pops it at the end of the function.
Also make sure that no other code in the function touches the frame
pointer.
Another possibility is that the code has some asm or inline asm which
does some unusual things to the stack or the frame pointer. In such
cases it's probably appropriate to use the CFI hint macros in
asm/undwarf.h.
Errors in .c files
------------------
1. c_file.o: warning: objtool: funcA() falls through to next function funcB()
8. file.o: warning: objtool: funcA() falls through to next function funcB()
This means that funcA() doesn't end with a return instruction or an
unconditional jump, and that objtool has determined that the function
@ -318,22 +311,6 @@ Errors in .c files
might be corrupt due to a gcc bug. For more details, see:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70646
2. If you're getting any other objtool error in a compiled .c file, it
may be because the file uses an asm() statement which has a "call"
instruction. An asm() statement with a call instruction must declare
the use of the stack pointer in its output operand. For example, on
x86_64:
register void *__sp asm("rsp");
asm volatile("call func" : "+r" (__sp));
Otherwise the stack frame may not get created before the call.
3. Another possible cause for errors in C code is if the Makefile removes
-fno-omit-frame-pointer or adds -fomit-frame-pointer to the gcc options.
Also see the above section for .S file errors for more information what
the individual error messages mean.
If the error doesn't seem to make sense, it could be a bug in objtool.
Feel free to ask the objtool maintainer for help.

2
tools/objtool/Makefile
View File

@ -25,7 +25,7 @@ OBJTOOL_IN := $(OBJTOOL)-in.o
all: $(OBJTOOL)
INCLUDES := -I$(srctree)/tools/include -I$(srctree)/tools/arch/$(HOSTARCH)/include/uapi
CFLAGS += -Wall -Werror $(EXTRA_WARNINGS) -fomit-frame-pointer -O2 -g $(INCLUDES)
CFLAGS += -Wall -Werror $(EXTRA_WARNINGS) -Wno-switch-default -Wno-switch-enum -fomit-frame-pointer -O2 -g $(INCLUDES)
LDFLAGS += -lelf $(LIBSUBCMD)
# Allow old libelf to be used:

64
tools/objtool/arch.h
View File

@ -19,25 +19,63 @@
#define _ARCH_H
#include <stdbool.h>
#include <linux/list.h>
#include "elf.h"
#include "cfi.h"
#define INSN_FP_SAVE 1
#define INSN_FP_SETUP 2
#define INSN_FP_RESTORE 3
#define INSN_JUMP_CONDITIONAL 4
#define INSN_JUMP_UNCONDITIONAL 5
#define INSN_JUMP_DYNAMIC 6
#define INSN_CALL 7
#define INSN_CALL_DYNAMIC 8
#define INSN_RETURN 9
#define INSN_CONTEXT_SWITCH 10
#define INSN_NOP 11
#define INSN_OTHER 12
#define INSN_JUMP_CONDITIONAL 1
#define INSN_JUMP_UNCONDITIONAL 2
#define INSN_JUMP_DYNAMIC 3
#define INSN_CALL 4
#define INSN_CALL_DYNAMIC 5
#define INSN_RETURN 6
#define INSN_CONTEXT_SWITCH 7
#define INSN_STACK 8
#define INSN_NOP 9
#define INSN_OTHER 10
#define INSN_LAST INSN_OTHER
enum op_dest_type {
OP_DEST_REG,
OP_DEST_REG_INDIRECT,
OP_DEST_MEM,
OP_DEST_PUSH,
OP_DEST_LEAVE,
};
struct op_dest {
enum op_dest_type type;
unsigned char reg;
int offset;
};
enum op_src_type {
OP_SRC_REG,
OP_SRC_REG_INDIRECT,
OP_SRC_CONST,
OP_SRC_POP,
OP_SRC_ADD,
OP_SRC_AND,
};
struct op_src {
enum op_src_type type;
unsigned char reg;
int offset;
};
struct stack_op {
struct op_dest dest;
struct op_src src;
};
void arch_initial_func_cfi_state(struct cfi_state *state);
int arch_decode_instruction(struct elf *elf, struct section *sec,
unsigned long offset, unsigned int maxlen,
unsigned int *len, unsigned char *type,
unsigned long *displacement);
unsigned long *immediate, struct stack_op *op);
bool arch_callee_saved_reg(unsigned char reg);
#endif /* _ARCH_H */

400
tools/objtool/arch/x86/decode.c
View File

@ -27,6 +27,17 @@
#include "../../arch.h"
#include "../../warn.h"
static unsigned char op_to_cfi_reg[][2] = {
{CFI_AX, CFI_R8},
{CFI_CX, CFI_R9},
{CFI_DX, CFI_R10},
{CFI_BX, CFI_R11},
{CFI_SP, CFI_R12},
{CFI_BP, CFI_R13},
{CFI_SI, CFI_R14},
{CFI_DI, CFI_R15},
};
static int is_x86_64(struct elf *elf)
{
switch (elf->ehdr.e_machine) {
@ -40,24 +51,50 @@ static int is_x86_64(struct elf *elf)
}
}
bool arch_callee_saved_reg(unsigned char reg)
{
switch (reg) {
case CFI_BP:
case CFI_BX:
case CFI_R12:
case CFI_R13:
case CFI_R14:
case CFI_R15:
return true;
case CFI_AX:
case CFI_CX:
case CFI_DX:
case CFI_SI:
case CFI_DI:
case CFI_SP:
case CFI_R8:
case CFI_R9:
case CFI_R10:
case CFI_R11:
case CFI_RA:
default:
return false;
}
}
int arch_decode_instruction(struct elf *elf, struct section *sec,
unsigned long offset, unsigned int maxlen,
unsigned int *len, unsigned char *type,
unsigned long *immediate)
unsigned long *immediate, struct stack_op *op)
{
struct insn insn;
int x86_64;
unsigned char op1, op2, ext;
int x86_64, sign;
unsigned char op1, op2, rex = 0, rex_b = 0, rex_r = 0, rex_w = 0,
modrm = 0, modrm_mod = 0, modrm_rm = 0, modrm_reg = 0,
sib = 0;
x86_64 = is_x86_64(elf);
if (x86_64 == -1)
return -1;
insn_init(&insn, (void *)(sec->data + offset), maxlen, x86_64);
insn_init(&insn, sec->data->d_buf + offset, maxlen, x86_64);
insn_get_length(&insn);
insn_get_opcode(&insn);
insn_get_modrm(&insn);
insn_get_immediate(&insn);
if (!insn_complete(&insn)) {
WARN_FUNC("can't decode instruction", sec, offset);
@ -73,67 +110,323 @@ int arch_decode_instruction(struct elf *elf, struct section *sec,
op1 = insn.opcode.bytes[0];
op2 = insn.opcode.bytes[1];
if (insn.rex_prefix.nbytes) {
rex = insn.rex_prefix.bytes[0];
rex_w = X86_REX_W(rex) >> 3;
rex_r = X86_REX_R(rex) >> 2;
rex_b = X86_REX_B(rex);
}
if (insn.modrm.nbytes) {
modrm = insn.modrm.bytes[0];
modrm_mod = X86_MODRM_MOD(modrm);
modrm_reg = X86_MODRM_REG(modrm);
modrm_rm = X86_MODRM_RM(modrm);
}
if (insn.sib.nbytes)
sib = insn.sib.bytes[0];
switch (op1) {
case 0x55:
if (!insn.rex_prefix.nbytes)
/* push rbp */
*type = INSN_FP_SAVE;
case 0x1:
case 0x29:
if (rex_w && !rex_b && modrm_mod == 3 && modrm_rm == 4) {
/* add/sub reg, %rsp */
*type = INSN_STACK;
op->src.type = OP_SRC_ADD;
op->src.reg = op_to_cfi_reg[modrm_reg][rex_r];
op->dest.type = OP_SRC_REG;
op->dest.reg = CFI_SP;
}
break;
case 0x5d:
if (!insn.rex_prefix.nbytes)
/* pop rbp */
*type = INSN_FP_RESTORE;
case 0x50 ... 0x57:
/* push reg */
*type = INSN_STACK;
op->src.type = OP_SRC_REG;
op->src.reg = op_to_cfi_reg[op1 & 0x7][rex_b];
op->dest.type = OP_DEST_PUSH;
break;
case 0x58 ... 0x5f:
/* pop reg */
*type = INSN_STACK;
op->src.type = OP_SRC_POP;
op->dest.type = OP_DEST_REG;
op->dest.reg = op_to_cfi_reg[op1 & 0x7][rex_b];
break;
case 0x68:
case 0x6a:
/* push immediate */
*type = INSN_STACK;
op->src.type = OP_SRC_CONST;
op->dest.type = OP_DEST_PUSH;
break;
case 0x70 ... 0x7f:
*type = INSN_JUMP_CONDITIONAL;
break;
case 0x81:
case 0x83:
if (rex != 0x48)
break;
if (modrm == 0xe4) {
/* and imm, %rsp */
*type = INSN_STACK;
op->src.type = OP_SRC_AND;
op->src.reg = CFI_SP;
op->src.offset = insn.immediate.value;
op->dest.type = OP_DEST_REG;
op->dest.reg = CFI_SP;
break;
}
if (modrm == 0xc4)
sign = 1;
else if (modrm == 0xec)
sign = -1;
else
break;
/* add/sub imm, %rsp */
*type = INSN_STACK;
op->src.type = OP_SRC_ADD;
op->src.reg = CFI_SP;
op->src.offset = insn.immediate.value * sign;
op->dest.type = OP_DEST_REG;
op->dest.reg = CFI_SP;
break;
case 0x89:
if (insn.rex_prefix.nbytes == 1 &&
insn.rex_prefix.bytes[0] == 0x48 &&
insn.modrm.nbytes && insn.modrm.bytes[0] == 0xe5)
/* mov rsp, rbp */
*type = INSN_FP_SETUP;
if (rex == 0x48 && modrm == 0xe5) {
/* mov %rsp, %rbp */
*type = INSN_STACK;
op->src.type = OP_SRC_REG;
op->src.reg = CFI_SP;
op->dest.type = OP_DEST_REG;
op->dest.reg = CFI_BP;
break;
}
/* fallthrough */
case 0x88:
if (!rex_b &&
(modrm_mod == 1 || modrm_mod == 2) && modrm_rm == 5) {
/* mov reg, disp(%rbp) */
*type = INSN_STACK;
op->src.type = OP_SRC_REG;
op->src.reg = op_to_cfi_reg[modrm_reg][rex_r];
op->dest.type = OP_DEST_REG_INDIRECT;
op->dest.reg = CFI_BP;
op->dest.offset = insn.displacement.value;
} else if (rex_w && !rex_b && modrm_rm == 4 && sib == 0x24) {
/* mov reg, disp(%rsp) */
*type = INSN_STACK;
op->src.type = OP_SRC_REG;
op->src.reg = op_to_cfi_reg[modrm_reg][rex_r];
op->dest.type = OP_DEST_REG_INDIRECT;
op->dest.reg = CFI_SP;
op->dest.offset = insn.displacement.value;
}
break;
case 0x8b:
if (rex_w && !rex_b && modrm_mod == 1 && modrm_rm == 5) {
/* mov disp(%rbp), reg */
*type = INSN_STACK;
op->src.type = OP_SRC_REG_INDIRECT;
op->src.reg = CFI_BP;
op->src.offset = insn.displacement.value;
op->dest.type = OP_DEST_REG;
op->dest.reg = op_to_cfi_reg[modrm_reg][rex_r];
} else if (rex_w && !rex_b && sib == 0x24 &&
modrm_mod != 3 && modrm_rm == 4) {
/* mov disp(%rsp), reg */
*type = INSN_STACK;
op->src.type = OP_SRC_REG_INDIRECT;
op->src.reg = CFI_SP;
op->src.offset = insn.displacement.value;
op->dest.type = OP_DEST_REG;
op->dest.reg = op_to_cfi_reg[modrm_reg][rex_r];
}
break;
case 0x8d:
if (insn.rex_prefix.nbytes &&
insn.rex_prefix.bytes[0] == 0x48 &&
insn.modrm.nbytes && insn.modrm.bytes[0] == 0x2c &&
insn.sib.nbytes && insn.sib.bytes[0] == 0x24)
/* lea %(rsp), %rbp */
*type = INSN_FP_SETUP;
if (rex == 0x48 && modrm == 0x65) {
/* lea -disp(%rbp), %rsp */
*type = INSN_STACK;
op->src.type = OP_SRC_ADD;
op->src.reg = CFI_BP;
op->src.offset = insn.displacement.value;
op->dest.type = OP_DEST_REG;
op->dest.reg = CFI_SP;
break;
}
if (rex == 0x4c && modrm == 0x54 && sib == 0x24 &&
insn.displacement.value == 8) {
/*
* lea 0x8(%rsp), %r10
*
* Here r10 is the "drap" pointer, used as a stack
* pointer helper when the stack gets realigned.
*/
*type = INSN_STACK;
op->src.type = OP_SRC_ADD;
op->src.reg = CFI_SP;
op->src.offset = 8;
op->dest.type = OP_DEST_REG;
op->dest.reg = CFI_R10;
break;
}
if (rex == 0x4c && modrm == 0x6c && sib == 0x24 &&
insn.displacement.value == 16) {
/*
* lea 0x10(%rsp), %r13
*
* Here r13 is the "drap" pointer, used as a stack
* pointer helper when the stack gets realigned.
*/
*type = INSN_STACK;
op->src.type = OP_SRC_ADD;
op->src.reg = CFI_SP;
op->src.offset = 16;
op->dest.type = OP_DEST_REG;
op->dest.reg = CFI_R13;
break;
}
if (rex == 0x49 && modrm == 0x62 &&
insn.displacement.value == -8) {
/*
* lea -0x8(%r10), %rsp
*
* Restoring rsp back to its original value after a
* stack realignment.
*/
*type = INSN_STACK;
op->src.type = OP_SRC_ADD;
op->src.reg = CFI_R10;
op->src.offset = -8;
op->dest.type = OP_DEST_REG;
op->dest.reg = CFI_SP;
break;
}
if (rex == 0x49 && modrm == 0x65 &&
insn.displacement.value == -16) {
/*
* lea -0x10(%r13), %rsp
*
* Restoring rsp back to its original value after a
* stack realignment.
*/
*type = INSN_STACK;
op->src.type = OP_SRC_ADD;
op->src.reg = CFI_R13;
op->src.offset = -16;
op->dest.type = OP_DEST_REG;
op->dest.reg = CFI_SP;
break;
}
break;
case 0x8f:
/* pop to mem */
*type = INSN_STACK;
op->src.type = OP_SRC_POP;
op->dest.type = OP_DEST_MEM;
break;
case 0x90:
*type = INSN_NOP;
break;
case 0x9c:
/* pushf */
*type = INSN_STACK;
op->src.type = OP_SRC_CONST;
op->dest.type = OP_DEST_PUSH;
break;
case 0x9d:
/* popf */
*type = INSN_STACK;
op->src.type = OP_SRC_POP;
op->dest.type = OP_DEST_MEM;
break;
case 0x0f:
if (op2 >= 0x80 && op2 <= 0x8f)
*type = INSN_JUMP_CONDITIONAL;
else if (op2 == 0x05 || op2 == 0x07 || op2 == 0x34 ||
op2 == 0x35)
/* sysenter, sysret */
*type = INSN_CONTEXT_SWITCH;
else if (op2 == 0x0d || op2 == 0x1f)
/* nopl/nopw */
*type = INSN_NOP;
else if (op2 == 0x01 && insn.modrm.nbytes &&
(insn.modrm.bytes[0] == 0xc2 ||
insn.modrm.bytes[0] == 0xd8))
/* vmlaunch, vmrun */
*type = INSN_CONTEXT_SWITCH;
else if (op2 == 0xa0 || op2 == 0xa8) {
/* push fs/gs */
*type = INSN_STACK;
op->src.type = OP_SRC_CONST;
op->dest.type = OP_DEST_PUSH;
} else if (op2 == 0xa1 || op2 == 0xa9) {
/* pop fs/gs */
*type = INSN_STACK;
op->src.type = OP_SRC_POP;
op->dest.type = OP_DEST_MEM;
}
break;
case 0xc9: /* leave */
*type = INSN_FP_RESTORE;
case 0xc9:
/*
* leave
*
* equivalent to:
* mov bp, sp
* pop bp
*/
*type = INSN_STACK;
op->dest.type = OP_DEST_LEAVE;
break;
case 0xe3: /* jecxz/jrcxz */
case 0xe3:
/* jecxz/jrcxz */
*type = INSN_JUMP_CONDITIONAL;
break;
@ -158,14 +451,27 @@ int arch_decode_instruction(struct elf *elf, struct section *sec,
break;
case 0xff:
ext = X86_MODRM_REG(insn.modrm.bytes[0]);
if (ext == 2 || ext == 3)
if (modrm_reg == 2 || modrm_reg == 3)
*type = INSN_CALL_DYNAMIC;
else if (ext == 4)
else if (modrm_reg == 4)
*type = INSN_JUMP_DYNAMIC;
else if (ext == 5) /*jmpf */
else if (modrm_reg == 5)
/* jmpf */
*type = INSN_CONTEXT_SWITCH;
else if (modrm_reg == 6) {
/* push from mem */
*type = INSN_STACK;
op->src.type = OP_SRC_CONST;
op->dest.type = OP_DEST_PUSH;
}
break;
default:
@ -176,3 +482,21 @@ int arch_decode_instruction(struct elf *elf, struct section *sec,
return 0;
}
void arch_initial_func_cfi_state(struct cfi_state *state)
{
int i;
for (i = 0; i < CFI_NUM_REGS; i++) {
state->regs[i].base = CFI_UNDEFINED;
state->regs[i].offset = 0;
}
/* initial CFA (call frame address) */
state->cfa.base = CFI_SP;
state->cfa.offset = 8;
/* initial RA (return address) */
state->regs[16].base = CFI_CFA;
state->regs[16].offset = -8;
}

55
tools/objtool/cfi.h Normal file
View File

@ -0,0 +1,55 @@
/*
* Copyright (C) 2015-2017 Josh Poimboeuf <jpoimboe@redhat.com>
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version 2
* of the License, or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, see <http://www.gnu.org/licenses/>.
*/
#ifndef _OBJTOOL_CFI_H
#define _OBJTOOL_CFI_H
#define CFI_UNDEFINED -1
#define CFI_CFA -2
#define CFI_SP_INDIRECT -3
#define CFI_BP_INDIRECT -4
#define CFI_AX 0
#define CFI_DX 1
#define CFI_CX 2
#define CFI_BX 3
#define CFI_SI 4
#define CFI_DI 5
#define CFI_BP 6
#define CFI_SP 7
#define CFI_R8 8
#define CFI_R9 9
#define CFI_R10 10
#define CFI_R11 11
#define CFI_R12 12
#define CFI_R13 13
#define CFI_R14 14
#define CFI_R15 15
#define CFI_RA 16
#define CFI_NUM_REGS 17
struct cfi_reg {
int base;
int offset;
};
struct cfi_state {
struct cfi_reg cfa;
struct cfi_reg regs[CFI_NUM_REGS];
};
#endif /* _OBJTOOL_CFI_H */

676
tools/objtool/check.c
View File

@ -27,10 +27,6 @@
#include <linux/hashtable.h>
#include <linux/kernel.h>
#define STATE_FP_SAVED 0x1
#define STATE_FP_SETUP 0x2
#define STATE_FENTRY 0x4
struct alternative {
struct list_head list;
struct instruction *insn;
@ -38,6 +34,7 @@ struct alternative {
const char *objname;
static bool nofp;
struct cfi_state initial_func_cfi;
static struct instruction *find_insn(struct objtool_file *file,
struct section *sec, unsigned long offset)
@ -56,7 +53,7 @@ static struct instruction *next_insn_same_sec(struct objtool_file *file,
{
struct instruction *next = list_next_entry(insn, list);
if (&next->list == &file->insn_list || next->sec != insn->sec)
if (!next || &next->list == &file->insn_list || next->sec != insn->sec)
return NULL;
return next;
@ -67,7 +64,7 @@ static bool gcov_enabled(struct objtool_file *file)
struct section *sec;
struct symbol *sym;
list_for_each_entry(sec, &file->elf->sections, list)
for_each_sec(file, sec)
list_for_each_entry(sym, &sec->symbol_list, list)
if (!strncmp(sym->name, "__gcov_.", 8))
return true;
@ -75,9 +72,6 @@ static bool gcov_enabled(struct objtool_file *file)
return false;
}
#define for_each_insn(file, insn) \
list_for_each_entry(insn, &file->insn_list, list)
#define func_for_each_insn(file, func, insn) \
for (insn = find_insn(file, func->sec, func->offset); \
insn && &insn->list != &file->insn_list && \
@ -94,6 +88,9 @@ static bool gcov_enabled(struct objtool_file *file)
#define sec_for_each_insn_from(file, insn) \
for (; insn; insn = next_insn_same_sec(file, insn))
#define sec_for_each_insn_continue(file, insn) \
for (insn = next_insn_same_sec(file, insn); insn; \
insn = next_insn_same_sec(file, insn))
/*
* Check if the function has been manually whitelisted with the
@ -103,7 +100,6 @@ static bool gcov_enabled(struct objtool_file *file)
static bool ignore_func(struct objtool_file *file, struct symbol *func)
{
struct rela *rela;
struct instruction *insn;
/* check for STACK_FRAME_NON_STANDARD */
if (file->whitelist && file->whitelist->rela)
@ -116,11 +112,6 @@ static bool ignore_func(struct objtool_file *file, struct symbol *func)
return true;
}
/* check if it has a context switching instruction */
func_for_each_insn(file, func, insn)
if (insn->type == INSN_CONTEXT_SWITCH)
return true;
return false;
}
@ -234,6 +225,17 @@ static int dead_end_function(struct objtool_file *file, struct symbol *func)
return __dead_end_function(file, func, 0);
}
static void clear_insn_state(struct insn_state *state)
{
int i;
memset(state, 0, sizeof(*state));
state->cfa.base = CFI_UNDEFINED;
for (i = 0; i < CFI_NUM_REGS; i++)
state->regs[i].base = CFI_UNDEFINED;
state->drap_reg = CFI_UNDEFINED;
}
/*
* Call the arch-specific instruction decoder for all the instructions and add
* them to the global instruction list.
@ -246,23 +248,29 @@ static int decode_instructions(struct objtool_file *file)
struct instruction *insn;
int ret;
list_for_each_entry(sec, &file->elf->sections, list) {
for_each_sec(file, sec) {
if (!(sec->sh.sh_flags & SHF_EXECINSTR))
continue;
for (offset = 0; offset < sec->len; offset += insn->len) {
insn = malloc(sizeof(*insn));
if (!insn) {
WARN("malloc failed");
return -1;
}
memset(insn, 0, sizeof(*insn));
INIT_LIST_HEAD(&insn->alts);
clear_insn_state(&insn->state);
insn->sec = sec;
insn->offset = offset;
ret = arch_decode_instruction(file->elf, sec, offset,
sec->len - offset,
&insn->len, &insn->type,
&insn->immediate);
&insn->immediate,
&insn->stack_op);
if (ret)
return ret;
@ -352,7 +360,7 @@ static void add_ignores(struct objtool_file *file)
struct section *sec;
struct symbol *func;
list_for_each_entry(sec, &file->elf->sections, list) {
for_each_sec(file, sec) {
list_for_each_entry(func, &sec->symbol_list, list) {
if (func->type != STT_FUNC)
continue;
@ -361,7 +369,7 @@ static void add_ignores(struct objtool_file *file)
continue;
func_for_each_insn(file, func, insn)
insn->visited = true;
insn->ignore = true;
}
}
}
@ -381,8 +389,7 @@ static int add_jump_destinations(struct objtool_file *file)
insn->type != INSN_JUMP_UNCONDITIONAL)
continue;
/* skip ignores */
if (insn->visited)
if (insn->ignore)
continue;
rela = find_rela_by_dest_range(insn->sec, insn->offset,
@ -519,10 +526,13 @@ static int handle_group_alt(struct objtool_file *file,
}
memset(fake_jump, 0, sizeof(*fake_jump));
INIT_LIST_HEAD(&fake_jump->alts);
clear_insn_state(&fake_jump->state);
fake_jump->sec = special_alt->new_sec;
fake_jump->offset = -1;
fake_jump->type = INSN_JUMP_UNCONDITIONAL;
fake_jump->jump_dest = list_next_entry(last_orig_insn, list);
fake_jump->ignore = true;
if (!special_alt->new_len) {
*new_insn = fake_jump;
@ -844,7 +854,7 @@ static int add_switch_table_alts(struct objtool_file *file)
if (!file->rodata || !file->rodata->rela)
return 0;
list_for_each_entry(sec, &file->elf->sections, list) {
for_each_sec(file, sec) {
list_for_each_entry(func, &sec->symbol_list, list) {
if (func->type != STT_FUNC)
continue;
@ -901,21 +911,423 @@ static bool is_fentry_call(struct instruction *insn)
return false;
}
static bool has_modified_stack_frame(struct instruction *insn)
static bool has_modified_stack_frame(struct insn_state *state)
{
return (insn->state & STATE_FP_SAVED) ||
(insn->state & STATE_FP_SETUP);
int i;
if (state->cfa.base != initial_func_cfi.cfa.base ||
state->cfa.offset != initial_func_cfi.cfa.offset ||
state->stack_size != initial_func_cfi.cfa.offset ||
state->drap)
return true;
for (i = 0; i < CFI_NUM_REGS; i++)
if (state->regs[i].base != initial_func_cfi.regs[i].base ||
state->regs[i].offset != initial_func_cfi.regs[i].offset)
return true;
return false;
}
static bool has_valid_stack_frame(struct instruction *insn)
static bool has_valid_stack_frame(struct insn_state *state)
{
return (insn->state & STATE_FP_SAVED) &&
(insn->state & STATE_FP_SETUP);
if (state->cfa.base == CFI_BP && state->regs[CFI_BP].base == CFI_CFA &&
state->regs[CFI_BP].offset == -16)
return true;
if (state->drap && state->regs[CFI_BP].base == CFI_BP)
return true;
return false;
}
static unsigned int frame_state(unsigned long state)
static void save_reg(struct insn_state *state, unsigned char reg, int base,
int offset)
{
return (state & (STATE_FP_SAVED | STATE_FP_SETUP));
if ((arch_callee_saved_reg(reg) ||
(state->drap && reg == state->drap_reg)) &&
state->regs[reg].base == CFI_UNDEFINED) {
state->regs[reg].base = base;
state->regs[reg].offset = offset;
}
}
static void restore_reg(struct insn_state *state, unsigned char reg)
{
state->regs[reg].base = CFI_UNDEFINED;
state->regs[reg].offset = 0;
}
/*
* A note about DRAP stack alignment:
*
* GCC has the concept of a DRAP register, which is used to help keep track of
* the stack pointer when aligning the stack. r10 or r13 is used as the DRAP
* register. The typical DRAP pattern is:
*
* 4c 8d 54 24 08 lea 0x8(%rsp),%r10
* 48 83 e4 c0 and $0xffffffffffffffc0,%rsp
* 41 ff 72 f8 pushq -0x8(%r10)
* 55 push %rbp
* 48 89 e5 mov %rsp,%rbp
* (more pushes)
* 41 52 push %r10
* ...
* 41 5a pop %r10
* (more pops)
* 5d pop %rbp
* 49 8d 62 f8 lea -0x8(%r10),%rsp
* c3 retq
*
* There are some variations in the epilogues, like:
*
* 5b pop %rbx
* 41 5a pop %r10
* 41 5c pop %r12
* 41 5d pop %r13
* 41 5e pop %r14
* c9 leaveq
* 49 8d 62 f8 lea -0x8(%r10),%rsp
* c3 retq
*
* and:
*
* 4c 8b 55 e8 mov -0x18(%rbp),%r10
* 48 8b 5d e0 mov -0x20(%rbp),%rbx
* 4c 8b 65 f0 mov -0x10(%rbp),%r12
* 4c 8b 6d f8 mov -0x8(%rbp),%r13
* c9 leaveq
* 49 8d 62 f8 lea -0x8(%r10),%rsp
* c3 retq
*
* Sometimes r13 is used as the DRAP register, in which case it's saved and
* restored beforehand:
*
* 41 55 push %r13
* 4c 8d 6c 24 10 lea 0x10(%rsp),%r13
* 48 83 e4 f0 and $0xfffffffffffffff0,%rsp
* ...
* 49 8d 65 f0 lea -0x10(%r13),%rsp
* 41 5d pop %r13
* c3 retq
*/
static int update_insn_state(struct instruction *insn, struct insn_state *state)
{
struct stack_op *op = &insn->stack_op;
struct cfi_reg *cfa = &state->cfa;
struct cfi_reg *regs = state->regs;
/* stack operations don't make sense with an undefined CFA */
if (cfa->base == CFI_UNDEFINED) {
if (insn->func) {
WARN_FUNC("undefined stack state", insn->sec, insn->offset);
return -1;
}
return 0;
}
switch (op->dest.type) {
case OP_DEST_REG:
switch (op->src.type) {
case OP_SRC_REG:
if (cfa->base == op->src.reg && cfa->base == CFI_SP &&
op->dest.reg == CFI_BP && regs[CFI_BP].base == CFI_CFA &&
regs[CFI_BP].offset == -cfa->offset) {
/* mov %rsp, %rbp */
cfa->base = op->dest.reg;
state->bp_scratch = false;
} else if (state->drap) {
/* drap: mov %rsp, %rbp */
regs[CFI_BP].base = CFI_BP;
regs[CFI_BP].offset = -state->stack_size;
state->bp_scratch = false;
} else if (!nofp) {
WARN_FUNC("unknown stack-related register move",
insn->sec, insn->offset);
return -1;
}
break;
case OP_SRC_ADD:
if (op->dest.reg == CFI_SP && op->src.reg == CFI_SP) {
/* add imm, %rsp */
state->stack_size -= op->src.offset;
if (cfa->base == CFI_SP)
cfa->offset -= op->src.offset;
break;
}
if (op->dest.reg == CFI_SP && op->src.reg == CFI_BP) {
/* lea disp(%rbp), %rsp */
state->stack_size = -(op->src.offset + regs[CFI_BP].offset);
break;
}
if (op->dest.reg != CFI_BP && op->src.reg == CFI_SP &&
cfa->base == CFI_SP) {
/* drap: lea disp(%rsp), %drap */
state->drap_reg = op->dest.reg;
break;
}
if (state->drap && op->dest.reg == CFI_SP &&
op->src.reg == state->drap_reg) {
/* drap: lea disp(%drap), %rsp */
cfa->base = CFI_SP;
cfa->offset = state->stack_size = -op->src.offset;
state->drap_reg = CFI_UNDEFINED;
state->drap = false;
break;
}
if (op->dest.reg == state->cfa.base) {
WARN_FUNC("unsupported stack register modification",
insn->sec, insn->offset);
return -1;
}
break;
case OP_SRC_AND:
if (op->dest.reg != CFI_SP ||
(state->drap_reg != CFI_UNDEFINED && cfa->base != CFI_SP) ||
(state->drap_reg == CFI_UNDEFINED && cfa->base != CFI_BP)) {
WARN_FUNC("unsupported stack pointer realignment",
insn->sec, insn->offset);
return -1;
}
if (state->drap_reg != CFI_UNDEFINED) {
/* drap: and imm, %rsp */
cfa->base = state->drap_reg;
cfa->offset = state->stack_size = 0;
state->drap = true;
}
/*
* Older versions of GCC (4.8ish) realign the stack
* without DRAP, with a frame pointer.
*/
break;
case OP_SRC_POP:
if (!state->drap && op->dest.type == OP_DEST_REG &&
op->dest.reg == cfa->base) {
/* pop %rbp */
cfa->base = CFI_SP;
}
if (regs[op->dest.reg].offset == -state->stack_size) {
if (state->drap && cfa->base == CFI_BP_INDIRECT &&
op->dest.type == OP_DEST_REG &&
op->dest.reg == state->drap_reg) {
/* drap: pop %drap */
cfa->base = state->drap_reg;
cfa->offset = 0;
}
restore_reg(state, op->dest.reg);
}
state->stack_size -= 8;
if (cfa->base == CFI_SP)
cfa->offset -= 8;
break;
case OP_SRC_REG_INDIRECT:
if (state->drap && op->src.reg == CFI_BP &&
op->src.offset == regs[op->dest.reg].offset) {
/* drap: mov disp(%rbp), %reg */
if (op->dest.reg == state->drap_reg) {
cfa->base = state->drap_reg;
cfa->offset = 0;
}
restore_reg(state, op->dest.reg);
} else if (op->src.reg == cfa->base &&
op->src.offset == regs[op->dest.reg].offset + cfa->offset) {
/* mov disp(%rbp), %reg */
/* mov disp(%rsp), %reg */
restore_reg(state, op->dest.reg);
}
break;
default:
WARN_FUNC("unknown stack-related instruction",
insn->sec, insn->offset);
return -1;
}
break;
case OP_DEST_PUSH:
state->stack_size += 8;
if (cfa->base == CFI_SP)
cfa->offset += 8;
if (op->src.type != OP_SRC_REG)
break;
if (state->drap) {
if (op->src.reg == cfa->base && op->src.reg == state->drap_reg) {
/* drap: push %drap */
cfa->base = CFI_BP_INDIRECT;
cfa->offset = -state->stack_size;
/* save drap so we know when to undefine it */
save_reg(state, op->src.reg, CFI_CFA, -state->stack_size);
} else if (op->src.reg == CFI_BP && cfa->base == state->drap_reg) {
/* drap: push %rbp */
state->stack_size = 0;
} else if (regs[op->src.reg].base == CFI_UNDEFINED) {
/* drap: push %reg */
save_reg(state, op->src.reg, CFI_BP, -state->stack_size);
}
} else {
/* push %reg */
save_reg(state, op->src.reg, CFI_CFA, -state->stack_size);
}
/* detect when asm code uses rbp as a scratch register */
if (!nofp && insn->func && op->src.reg == CFI_BP &&
cfa->base != CFI_BP)
state->bp_scratch = true;
break;
case OP_DEST_REG_INDIRECT:
if (state->drap) {
if (op->src.reg == cfa->base && op->src.reg == state->drap_reg) {
/* drap: mov %drap, disp(%rbp) */
cfa->base = CFI_BP_INDIRECT;
cfa->offset = op->dest.offset;
/* save drap so we know when to undefine it */
save_reg(state, op->src.reg, CFI_CFA, op->dest.offset);
}
else if (regs[op->src.reg].base == CFI_UNDEFINED) {
/* drap: mov reg, disp(%rbp) */
save_reg(state, op->src.reg, CFI_BP, op->dest.offset);
}
} else if (op->dest.reg == cfa->base) {
/* mov reg, disp(%rbp) */
/* mov reg, disp(%rsp) */
save_reg(state, op->src.reg, CFI_CFA,
op->dest.offset - state->cfa.offset);
}
break;
case OP_DEST_LEAVE:
if ((!state->drap && cfa->base != CFI_BP) ||
(state->drap && cfa->base != state->drap_reg)) {
WARN_FUNC("leave instruction with modified stack frame",
insn->sec, insn->offset);
return -1;
}
/* leave (mov %rbp, %rsp; pop %rbp) */
state->stack_size = -state->regs[CFI_BP].offset - 8;
restore_reg(state, CFI_BP);
if (!state->drap) {
cfa->base = CFI_SP;
cfa->offset -= 8;
}
break;
case OP_DEST_MEM:
if (op->src.type != OP_SRC_POP) {
WARN_FUNC("unknown stack-related memory operation",
insn->sec, insn->offset);
return -1;
}
/* pop mem */
state->stack_size -= 8;
if (cfa->base == CFI_SP)
cfa->offset -= 8;
break;
default:
WARN_FUNC("unknown stack-related instruction",
insn->sec, insn->offset);
return -1;
}
return 0;
}
static bool insn_state_match(struct instruction *insn, struct insn_state *state)
{
struct insn_state *state1 = &insn->state, *state2 = state;
int i;
if (memcmp(&state1->cfa, &state2->cfa, sizeof(state1->cfa))) {
WARN_FUNC("stack state mismatch: cfa1=%d%+d cfa2=%d%+d",
insn->sec, insn->offset,
state1->cfa.base, state1->cfa.offset,
state2->cfa.base, state2->cfa.offset);
} else if (memcmp(&state1->regs, &state2->regs, sizeof(state1->regs))) {
for (i = 0; i < CFI_NUM_REGS; i++) {
if (!memcmp(&state1->regs[i], &state2->regs[i],
sizeof(struct cfi_reg)))
continue;
WARN_FUNC("stack state mismatch: reg1[%d]=%d%+d reg2[%d]=%d%+d",
insn->sec, insn->offset,
i, state1->regs[i].base, state1->regs[i].offset,
i, state2->regs[i].base, state2->regs[i].offset);
break;
}
} else if (state1->drap != state2->drap ||
(state1->drap && state1->drap_reg != state2->drap_reg)) {
WARN_FUNC("stack state mismatch: drap1=%d(%d) drap2=%d(%d)",
insn->sec, insn->offset,
state1->drap, state1->drap_reg,
state2->drap, state2->drap_reg);
} else
return true;
return false;
}
/*
@ -924,24 +1336,22 @@ static unsigned int frame_state(unsigned long state)
* each instruction and validate all the rules described in
* tools/objtool/Documentation/stack-validation.txt.
*/
static int validate_branch(struct objtool_file *file,
struct instruction *first, unsigned char first_state)
static int validate_branch(struct objtool_file *file, struct instruction *first,
struct insn_state state)
{
struct alternative *alt;
struct instruction *insn;
struct section *sec;
struct symbol *func = NULL;
unsigned char state;
int ret;
insn = first;
sec = insn->sec;
state = first_state;
if (insn->alt_group && list_empty(&insn->alts)) {
WARN_FUNC("don't know how to handle branch to middle of alternative instruction group",
sec, insn->offset);
return 1;
return -1;
}
while (1) {
@ -951,23 +1361,21 @@ static int validate_branch(struct objtool_file *file,
func->name, insn->func->name);
return 1;
}
func = insn->func;
}
func = insn->func;
if (insn->visited) {
if (frame_state(insn->state) != frame_state(state)) {
WARN_FUNC("frame pointer state mismatch",
sec, insn->offset);
if (!!insn_state_match(insn, &state))
return 1;
}
return 0;
}
insn->visited = true;
insn->state = state;
insn->visited = true;
list_for_each_entry(alt, &insn->alts, list) {
ret = validate_branch(file, alt->insn, state);
if (ret)
@ -976,50 +1384,24 @@ static int validate_branch(struct objtool_file *file,
switch (insn->type) {
case INSN_FP_SAVE:
if (!nofp) {
if (state & STATE_FP_SAVED) {
WARN_FUNC("duplicate frame pointer save",
sec, insn->offset);
return 1;
}
state |= STATE_FP_SAVED;
}
break;
case INSN_FP_SETUP:
if (!nofp) {
if (state & STATE_FP_SETUP) {
WARN_FUNC("duplicate frame pointer setup",
sec, insn->offset);
return 1;
}
state |= STATE_FP_SETUP;
}
break;
case INSN_FP_RESTORE:
if (!nofp) {
if (has_valid_stack_frame(insn))
state &= ~STATE_FP_SETUP;
state &= ~STATE_FP_SAVED;
}
break;
case INSN_RETURN:
if (!nofp && has_modified_stack_frame(insn)) {
WARN_FUNC("return without frame pointer restore",
if (func && has_modified_stack_frame(&state)) {
WARN_FUNC("return with modified stack frame",
sec, insn->offset);
return 1;
}
if (state.bp_scratch) {
WARN("%s uses BP as a scratch register",
insn->func->name);
return 1;
}
return 0;
case INSN_CALL:
if (is_fentry_call(insn)) {
state |= STATE_FENTRY;
if (is_fentry_call(insn))
break;
}
ret = dead_end_function(file, insn->call_dest);
if (ret == 1)
@ -1029,7 +1411,7 @@ static int validate_branch(struct objtool_file *file,
/* fallthrough */
case INSN_CALL_DYNAMIC:
if (!nofp && !has_valid_stack_frame(insn)) {
if (!nofp && func && !has_valid_stack_frame(&state)) {
WARN_FUNC("call without frame pointer save/setup",
sec, insn->offset);
return 1;
@ -1043,8 +1425,8 @@ static int validate_branch(struct objtool_file *file,
state);
if (ret)
return 1;
} else if (has_modified_stack_frame(insn)) {
WARN_FUNC("sibling call from callable instruction with changed frame pointer",
} else if (func && has_modified_stack_frame(&state)) {
WARN_FUNC("sibling call from callable instruction with modified stack frame",
sec, insn->offset);
return 1;
} /* else it's a sibling call */
@ -1055,15 +1437,29 @@ static int validate_branch(struct objtool_file *file,
break;
case INSN_JUMP_DYNAMIC:
if (list_empty(&insn->alts) &&
has_modified_stack_frame(insn)) {
WARN_FUNC("sibling call from callable instruction with changed frame pointer",
if (func && list_empty(&insn->alts) &&
has_modified_stack_frame(&state)) {
WARN_FUNC("sibling call from callable instruction with modified stack frame",
sec, insn->offset);
return 1;
}
return 0;
case INSN_CONTEXT_SWITCH:
if (func) {
WARN_FUNC("unsupported instruction in callable function",
sec, insn->offset);
return 1;
}
return 0;
case INSN_STACK:
if (update_insn_state(insn, &state))
return -1;
break;
default:
break;
}
@ -1094,12 +1490,18 @@ static bool is_ubsan_insn(struct instruction *insn)
"__ubsan_handle_builtin_unreachable"));
}
static bool ignore_unreachable_insn(struct symbol *func,
struct instruction *insn)
static bool ignore_unreachable_insn(struct instruction *insn)
{
int i;
if (insn->type == INSN_NOP)
if (insn->ignore || insn->type == INSN_NOP)
return true;
/*
* Ignore any unused exceptions. This can happen when a whitelisted
* function has an exception table entry.
*/
if (!strcmp(insn->sec->name, ".fixup"))
return true;
/*
@ -1108,6 +1510,8 @@ static bool ignore_unreachable_insn(struct symbol *func,
*
* End the search at 5 instructions to avoid going into the weeds.
*/
if (!insn->func)
return false;
for (i = 0; i < 5; i++) {
if (is_kasan_insn(insn) || is_ubsan_insn(insn))
@ -1118,7 +1522,7 @@ static bool ignore_unreachable_insn(struct symbol *func,
continue;
}
if (insn->offset + insn->len >= func->offset + func->len)
if (insn->offset + insn->len >= insn->func->offset + insn->func->len)
break;
insn = list_next_entry(insn, list);
}
@ -1131,73 +1535,58 @@ static int validate_functions(struct objtool_file *file)
struct section *sec;
struct symbol *func;
struct instruction *insn;
struct insn_state state;
int ret, warnings = 0;
list_for_each_entry(sec, &file->elf->sections, list) {
clear_insn_state(&state);
state.cfa = initial_func_cfi.cfa;
memcpy(&state.regs, &initial_func_cfi.regs,
CFI_NUM_REGS * sizeof(struct cfi_reg));
state.stack_size = initial_func_cfi.cfa.offset;
for_each_sec(file, sec) {
list_for_each_entry(func, &sec->symbol_list, list) {
if (func->type != STT_FUNC)
continue;
insn = find_insn(file, sec, func->offset);
if (!insn)
if (!insn || insn->ignore)
continue;
ret = validate_branch(file, insn, 0);
ret = validate_branch(file, insn, state);
warnings += ret;
}
}
list_for_each_entry(sec, &file->elf->sections, list) {
list_for_each_entry(func, &sec->symbol_list, list) {
if (func->type != STT_FUNC)
continue;
func_for_each_insn(file, func, insn) {
if (insn->visited)
continue;
insn->visited = true;
if (file->ignore_unreachables || warnings ||
ignore_unreachable_insn(func, insn))
continue;
/*
* gcov produces a lot of unreachable
* instructions. If we get an unreachable
* warning and the file has gcov enabled, just
* ignore it, and all other such warnings for
* the file.
*/
if (!file->ignore_unreachables &&
gcov_enabled(file)) {
file->ignore_unreachables = true;
continue;
}
WARN_FUNC("function has unreachable instruction", insn->sec, insn->offset);
warnings++;
}
}
}
return warnings;
}
static int validate_uncallable_instructions(struct objtool_file *file)
static int validate_reachable_instructions(struct objtool_file *file)
{
struct instruction *insn;
int warnings = 0;
if (file->ignore_unreachables)
return 0;
for_each_insn(file, insn) {
if (!insn->visited && insn->type == INSN_RETURN) {
WARN_FUNC("return instruction outside of a callable function",
insn->sec, insn->offset);
warnings++;
}
if (insn->visited || ignore_unreachable_insn(insn))
continue;
/*
* gcov produces a lot of unreachable instructions. If we get
* an unreachable warning and the file has gcov enabled, just
* ignore it, and all other such warnings for the file. Do
* this here because this is an expensive function.
*/
if (gcov_enabled(file))
return 0;
WARN_FUNC("unreachable instruction", insn->sec, insn->offset);
return 1;
}
return warnings;
return 0;
}
static void cleanup(struct objtool_file *file)
@ -1226,10 +1615,8 @@ int check(const char *_objname, bool _nofp)
nofp = _nofp;
file.elf = elf_open(objname);
if (!file.elf) {
fprintf(stderr, "error reading elf file %s\n", objname);
if (!file.elf)
return 1;
}
INIT_LIST_HEAD(&file.insn_list);
hash_init(file.insn_hash);
@ -1238,20 +1625,27 @@ int check(const char *_objname, bool _nofp)
file.ignore_unreachables = false;
file.c_file = find_section_by_name(file.elf, ".comment");
arch_initial_func_cfi_state(&initial_func_cfi);
ret = decode_sections(&file);
if (ret < 0)
goto out;
warnings += ret;
if (list_empty(&file.insn_list))
goto out;
ret = validate_functions(&file);
if (ret < 0)
goto out;
warnings += ret;
ret = validate_uncallable_instructions(&file);
if (ret < 0)
goto out;
warnings += ret;
if (!warnings) {
ret = validate_reachable_instructions(&file);
if (ret < 0)
goto out;
warnings += ret;
}
out:
cleanup(&file);

19
tools/objtool/check.h
View File

@ -20,22 +20,34 @@
#include <stdbool.h>
#include "elf.h"
#include "cfi.h"
#include "arch.h"
#include <linux/hashtable.h>
struct insn_state {
struct cfi_reg cfa;
struct cfi_reg regs[CFI_NUM_REGS];
int stack_size;
bool bp_scratch;
bool drap;
int drap_reg;
};
struct instruction {
struct list_head list;
struct hlist_node hash;
struct section *sec;
unsigned long offset;
unsigned int len, state;
unsigned int len;
unsigned char type;
unsigned long immediate;
bool alt_group, visited, dead_end;
bool alt_group, visited, dead_end, ignore;
struct symbol *call_dest;
struct instruction *jump_dest;
struct list_head alts;
struct symbol *func;
struct stack_op stack_op;
struct insn_state state;
};
struct objtool_file {
@ -48,4 +60,7 @@ struct objtool_file {
int check(const char *objname, bool nofp);
#define for_each_insn(file, insn) \
list_for_each_entry(insn, &file->insn_list, list)
#endif /* _CHECK_H */

59
tools/objtool/elf.c
View File

@ -37,6 +37,9 @@
#define ELF_C_READ_MMAP ELF_C_READ
#endif
#define WARN_ELF(format, ...) \
WARN(format ": %s", ##__VA_ARGS__, elf_errmsg(-1))
struct section *find_section_by_name(struct elf *elf, const char *name)
{
struct section *sec;
@ -139,12 +142,12 @@ static int read_sections(struct elf *elf)
int i;
if (elf_getshdrnum(elf->elf, &sections_nr)) {
perror("elf_getshdrnum");
WARN_ELF("elf_getshdrnum");
return -1;
}
if (elf_getshdrstrndx(elf->elf, &shstrndx)) {
perror("elf_getshdrstrndx");
WARN_ELF("elf_getshdrstrndx");
return -1;
}
@ -165,37 +168,36 @@ static int read_sections(struct elf *elf)
s = elf_getscn(elf->elf, i);
if (!s) {
perror("elf_getscn");
WARN_ELF("elf_getscn");
return -1;
}
sec->idx = elf_ndxscn(s);
if (!gelf_getshdr(s, &sec->sh)) {
perror("gelf_getshdr");
WARN_ELF("gelf_getshdr");
return -1;
}
sec->name = elf_strptr(elf->elf, shstrndx, sec->sh.sh_name);
if (!sec->name) {
perror("elf_strptr");
WARN_ELF("elf_strptr");
return -1;
}
sec->elf_data = elf_getdata(s, NULL);
if (!sec->elf_data) {
perror("elf_getdata");
sec->data = elf_getdata(s, NULL);
if (!sec->data) {
WARN_ELF("elf_getdata");
return -1;
}
if (sec->elf_data->d_off != 0 ||
sec->elf_data->d_size != sec->sh.sh_size) {
if (sec->data->d_off != 0 ||
sec->data->d_size != sec->sh.sh_size) {
WARN("unexpected data attributes for %s", sec->name);
return -1;
}
sec->data = (unsigned long)sec->elf_data->d_buf;
sec->len = sec->elf_data->d_size;
sec->len = sec->data->d_size;
}
/* sanity check, one more call to elf_nextscn() should return NULL */
@ -232,15 +234,15 @@ static int read_symbols(struct elf *elf)
sym->idx = i;
if (!gelf_getsym(symtab->elf_data, i, &sym->sym)) {
perror("gelf_getsym");
if (!gelf_getsym(symtab->data, i, &sym->sym)) {
WARN_ELF("gelf_getsym");
goto err;
}
sym->name = elf_strptr(elf->elf, symtab->sh.sh_link,
sym->sym.st_name);
if (!sym->name) {
perror("elf_strptr");
WARN_ELF("elf_strptr");
goto err;
}
@ -322,8 +324,8 @@ static int read_relas(struct elf *elf)
}
memset(rela, 0, sizeof(*rela));
if (!gelf_getrela(sec->elf_data, i, &rela->rela)) {
perror("gelf_getrela");
if (!gelf_getrela(sec->data, i, &rela->rela)) {
WARN_ELF("gelf_getrela");
return -1;
}
@ -362,12 +364,6 @@ struct elf *elf_open(const char *name)
INIT_LIST_HEAD(&elf->sections);
elf->name = strdup(name);
if (!elf->name) {
perror("strdup");
goto err;
}
elf->fd = open(name, O_RDONLY);
if (elf->fd == -1) {
perror("open");
@ -376,12 +372,12 @@ struct elf *elf_open(const char *name)
elf->elf = elf_begin(elf->fd, ELF_C_READ_MMAP, NULL);
if (!elf->elf) {
perror("elf_begin");
WARN_ELF("elf_begin");
goto err;
}
if (!gelf_getehdr(elf->elf, &elf->ehdr)) {
perror("gelf_getehdr");
WARN_ELF("gelf_getehdr");
goto err;
}
@ -407,6 +403,12 @@ void elf_close(struct elf *elf)
struct symbol *sym, *tmpsym;
struct rela *rela, *tmprela;
if (elf->elf)
elf_end(elf->elf);
if (elf->fd > 0)
close(elf->fd);
list_for_each_entry_safe(sec, tmpsec, &elf->sections, list) {
list_for_each_entry_safe(sym, tmpsym, &sec->symbol_list, list) {
list_del(&sym->list);
@ -421,11 +423,6 @@ void elf_close(struct elf *elf)
list_del(&sec->list);
free(sec);
}
if (elf->name)
free(elf->name);
if (elf->fd > 0)
close(elf->fd);
if (elf->elf)
elf_end(elf->elf);
free(elf);
}

6
tools/objtool/elf.h
View File

@ -37,10 +37,9 @@ struct section {
DECLARE_HASHTABLE(rela_hash, 16);
struct section *base, *rela;
struct symbol *sym;
Elf_Data *elf_data;
Elf_Data *data;
char *name;
int idx;
unsigned long data;
unsigned int len;
};
@ -86,6 +85,7 @@ struct rela *find_rela_by_dest_range(struct section *sec, unsigned long offset,
struct symbol *find_containing_func(struct section *sec, unsigned long offset);
void elf_close(struct elf *elf);
#define for_each_sec(file, sec) \
list_for_each_entry(sec, &file->elf->sections, list)
#endif /* _OBJTOOL_ELF_H */

6
tools/objtool/special.c
View File

@ -91,16 +91,16 @@ static int get_alt_entry(struct elf *elf, struct special_entry *entry,
alt->jump_or_nop = entry->jump_or_nop;
if (alt->group) {
alt->orig_len = *(unsigned char *)(sec->data + offset +
alt->orig_len = *(unsigned char *)(sec->data->d_buf + offset +
entry->orig_len);
alt->new_len = *(unsigned char *)(sec->data + offset +
alt->new_len = *(unsigned char *)(sec->data->d_buf + offset +
entry->new_len);
}
if (entry->feature) {
unsigned short feature;
feature = *(unsigned short *)(sec->data + offset +
feature = *(unsigned short *)(sec->data->d_buf + offset +
entry->feature);
/*

10
tools/objtool/warn.h
View File

@ -18,6 +18,13 @@
#ifndef _WARN_H
#define _WARN_H
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include "elf.h"
extern const char *objname;
static inline char *offstr(struct section *sec, unsigned long offset)
@ -57,4 +64,7 @@ static inline char *offstr(struct section *sec, unsigned long offset)
free(_str); \
})
#define WARN_ELF(format, ...) \
WARN(format ": %s", ##__VA_ARGS__, elf_errmsg(-1))
#endif /* _WARN_H */