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x86/unwinder: Handle stack overflows more gracefully

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There are at least two unwinder bugs hindering the debugging of
stack-overflow crashes:

- It doesn't deal gracefully with the case where the stack overflows and
  the stack pointer itself isn't on a valid stack but the
  to-be-dereferenced data *is*.

- The ORC oops dump code doesn't know how to print partial pt_regs, for the
  case where if we get an interrupt/exception in *early* entry code
  before the full pt_regs have been saved.

Fix both issues.

http://lkml.kernel.org/r/20171126024031.uxi4numpbjm5rlbr@treble

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Borislav Petkov <bpetkov@suse.de>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: David Laight <David.Laight@aculab.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Eduardo Valentin <eduval@amazon.com>
Cc: Greg KH <gregkh@linuxfoundation.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: aliguori@amazon.com
Cc: daniel.gruss@iaik.tugraz.at
Cc: hughd@google.com
Cc: keescook@google.com
Link: https://lkml.kernel.org/r/20171204150605.071425003@linutronix.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Josh Poimboeuf 2017-12-04 15:07:09 +01:00 committed by Ingo Molnar
parent d3a0910401
commit b02fcf9ba1
5 changed files with 65 additions and 60 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
arch/x86/include/asm/kdebug.h
View File

@ -26,6 +26,7 @@ extern void die(const char *, struct pt_regs *,long);
extern int __must_check __die(const char *, struct pt_regs *, long);
extern void show_stack_regs(struct pt_regs *regs);
extern void __show_regs(struct pt_regs *regs, int all);
extern void show_iret_regs(struct pt_regs *regs);
extern unsigned long oops_begin(void);
extern void oops_end(unsigned long, struct pt_regs *, int signr);

7
arch/x86/include/asm/unwind.h
View File

@ -7,6 +7,9 @@
#include <asm/ptrace.h>
#include <asm/stacktrace.h>
#define IRET_FRAME_OFFSET (offsetof(struct pt_regs, ip))
#define IRET_FRAME_SIZE (sizeof(struct pt_regs) - IRET_FRAME_OFFSET)
struct unwind_state {
struct stack_info stack_info;
unsigned long stack_mask;
@ -52,6 +55,10 @@ void unwind_start(struct unwind_state *state, struct task_struct *task,
}
#if defined(CONFIG_UNWINDER_ORC) || defined(CONFIG_UNWINDER_FRAME_POINTER)
/*
* WARNING: The entire pt_regs may not be safe to dereference. In some cases,
* only the iret frame registers are accessible. Use with caution!
*/
static inline struct pt_regs *unwind_get_entry_regs(struct unwind_state *state)
{
if (unwind_done(state))

32
arch/x86/kernel/dumpstack.c
View File

@ -50,6 +50,28 @@ static void printk_stack_address(unsigned long address, int reliable,
printk("%s %s%pB\n", log_lvl, reliable ? "" : "? ", (void *)address);
}
void show_iret_regs(struct pt_regs *regs)
{
printk(KERN_DEFAULT "RIP: %04x:%pS\n", (int)regs->cs, (void *)regs->ip);
printk(KERN_DEFAULT "RSP: %04x:%016lx EFLAGS: %08lx", (int)regs->ss,
regs->sp, regs->flags);
}
static void show_regs_safe(struct stack_info *info, struct pt_regs *regs)
{
if (on_stack(info, regs, sizeof(*regs)))
__show_regs(regs, 0);
else if (on_stack(info, (void *)regs + IRET_FRAME_OFFSET,
IRET_FRAME_SIZE)) {
/*
* When an interrupt or exception occurs in entry code, the
* full pt_regs might not have been saved yet. In that case
* just print the iret frame.
*/
show_iret_regs(regs);
}
}
void show_trace_log_lvl(struct task_struct *task, struct pt_regs *regs,
unsigned long *stack, char *log_lvl)
{
@ -94,8 +116,8 @@ void show_trace_log_lvl(struct task_struct *task, struct pt_regs *regs,
if (stack_name)
printk("%s <%s>\n", log_lvl, stack_name);
if (regs && on_stack(&stack_info, regs, sizeof(*regs)))
__show_regs(regs, 0);
if (regs)
show_regs_safe(&stack_info, regs);
/*
* Scan the stack, printing any text addresses we find. At the
@ -119,7 +141,7 @@ void show_trace_log_lvl(struct task_struct *task, struct pt_regs *regs,
/*
* Don't print regs->ip again if it was already printed
* by __show_regs() below.
* by show_regs_safe() below.
*/
if (regs && stack == &regs->ip)
goto next;
@ -155,8 +177,8 @@ next:
/* if the frame has entry regs, print them */
regs = unwind_get_entry_regs(&state);
if (regs && on_stack(&stack_info, regs, sizeof(*regs)))
__show_regs(regs, 0);
if (regs)
show_regs_safe(&stack_info, regs);
}
if (stack_name)

11
arch/x86/kernel/process_64.c
View File

@ -69,9 +69,8 @@ void __show_regs(struct pt_regs *regs, int all)
unsigned int fsindex, gsindex;
unsigned int ds, cs, es;
printk(KERN_DEFAULT "RIP: %04lx:%pS\n", regs->cs, (void *)regs->ip);
printk(KERN_DEFAULT "RSP: %04lx:%016lx EFLAGS: %08lx", regs->ss,
regs->sp, regs->flags);
show_iret_regs(regs);
if (regs->orig_ax != -1)
pr_cont(" ORIG_RAX: %016lx\n", regs->orig_ax);
else
@ -88,6 +87,9 @@ void __show_regs(struct pt_regs *regs, int all)
printk(KERN_DEFAULT "R13: %016lx R14: %016lx R15: %016lx\n",
regs->r13, regs->r14, regs->r15);
if (!all)
return;
asm("movl %%ds,%0" : "=r" (ds));
asm("movl %%cs,%0" : "=r" (cs));
asm("movl %%es,%0" : "=r" (es));
@ -98,9 +100,6 @@ void __show_regs(struct pt_regs *regs, int all)
rdmsrl(MSR_GS_BASE, gs);
rdmsrl(MSR_KERNEL_GS_BASE, shadowgs);
if (!all)
return;
cr0 = read_cr0();
cr2 = read_cr2();
cr3 = __read_cr3();

74
arch/x86/kernel/unwind_orc.c
View File

@ -253,22 +253,15 @@ unsigned long *unwind_get_return_address_ptr(struct unwind_state *state)
return NULL;
}
static bool stack_access_ok(struct unwind_state *state, unsigned long addr,
static bool stack_access_ok(struct unwind_state *state, unsigned long _addr,
size_t len)
{
struct stack_info *info = &state->stack_info;
void *addr = (void *)_addr;
/*
* If the address isn't on the current stack, switch to the next one.
*
* We may have to traverse multiple stacks to deal with the possibility
* that info->next_sp could point to an empty stack and the address
* could be on a subsequent stack.
*/
while (!on_stack(info, (void *)addr, len))
if (get_stack_info(info->next_sp, state->task, info,
&state->stack_mask))
return false;
if (!on_stack(info, addr, len) &&
(get_stack_info(addr, state->task, info, &state->stack_mask)))
return false;
return true;
}
@ -283,42 +276,32 @@ static bool deref_stack_reg(struct unwind_state *state, unsigned long addr,
return true;
}
#define REGS_SIZE (sizeof(struct pt_regs))
#define SP_OFFSET (offsetof(struct pt_regs, sp))
#define IRET_REGS_SIZE (REGS_SIZE - offsetof(struct pt_regs, ip))
#define IRET_SP_OFFSET (SP_OFFSET - offsetof(struct pt_regs, ip))
static bool deref_stack_regs(struct unwind_state *state, unsigned long addr,
unsigned long *ip, unsigned long *sp, bool full)
unsigned long *ip, unsigned long *sp)
{
size_t regs_size = full ? REGS_SIZE : IRET_REGS_SIZE;
size_t sp_offset = full ? SP_OFFSET : IRET_SP_OFFSET;
struct pt_regs *regs = (struct pt_regs *)(addr + regs_size - REGS_SIZE);
struct pt_regs *regs = (struct pt_regs *)addr;
if (IS_ENABLED(CONFIG_X86_64)) {
if (!stack_access_ok(state, addr, regs_size))
return false;
/* x86-32 support will be more complicated due to the &regs->sp hack */
BUILD_BUG_ON(IS_ENABLED(CONFIG_X86_32));
*ip = regs->ip;
*sp = regs->sp;
return true;
}
if (!stack_access_ok(state, addr, sp_offset))
if (!stack_access_ok(state, addr, sizeof(struct pt_regs)))
return false;
*ip = regs->ip;
*sp = regs->sp;
return true;
}
if (user_mode(regs)) {
if (!stack_access_ok(state, addr + sp_offset,
REGS_SIZE - SP_OFFSET))
return false;
static bool deref_stack_iret_regs(struct unwind_state *state, unsigned long addr,
unsigned long *ip, unsigned long *sp)
{
struct pt_regs *regs = (void *)addr - IRET_FRAME_OFFSET;
*sp = regs->sp;
} else
*sp = (unsigned long)&regs->sp;
if (!stack_access_ok(state, addr, IRET_FRAME_SIZE))
return false;
*ip = regs->ip;
*sp = regs->sp;
return true;
}
@ -327,7 +310,6 @@ bool unwind_next_frame(struct unwind_state *state)
unsigned long ip_p, sp, orig_ip, prev_sp = state->sp;
enum stack_type prev_type = state->stack_info.type;
struct orc_entry *orc;
struct pt_regs *ptregs;
bool indirect = false;
if (unwind_done(state))
@ -435,7 +417,7 @@ bool unwind_next_frame(struct unwind_state *state)
break;
case ORC_TYPE_REGS:
if (!deref_stack_regs(state, sp, &state->ip, &state->sp, true)) {
if (!deref_stack_regs(state, sp, &state->ip, &state->sp)) {
orc_warn("can't dereference registers at %p for ip %pB\n",
(void *)sp, (void *)orig_ip);
goto done;
@ -447,20 +429,14 @@ bool unwind_next_frame(struct unwind_state *state)
break;
case ORC_TYPE_REGS_IRET:
if (!deref_stack_regs(state, sp, &state->ip, &state->sp, false)) {
if (!deref_stack_iret_regs(state, sp, &state->ip, &state->sp)) {
orc_warn("can't dereference iret registers at %p for ip %pB\n",
(void *)sp, (void *)orig_ip);
goto done;
}
ptregs = container_of((void *)sp, struct pt_regs, ip);
if ((unsigned long)ptregs >= prev_sp &&
on_stack(&state->stack_info, ptregs, REGS_SIZE)) {
state->regs = ptregs;
state->full_regs = false;
} else
state->regs = NULL;
state->regs = (void *)sp - IRET_FRAME_OFFSET;
state->full_regs = false;
state->signal = true;
break;