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linux-next/arch/x86/include/asm/calling.h
Denys Vlasenko fc3e958a2b x86/asm/entry: Clear EXTRA_REGS for all executable formats 
On failure, sys_execve() does not clobber EXTRA_REGS, so we can
just return to userpsace without saving/restoring them.

On success, ELF_PLAT_INIT() in sys_execve() clears all these
registers.

On other executable formats:

  - binfmt_flat.c has similar FLAT_PLAT_INIT, but x86 (and everyone
    else except sh) doesn't define it.

  - binfmt_elf_fdpic.c has ELF_FDPIC_PLAT_INIT, but x86 (and most
    others) doesn't define it.

  - There are no such hooks in binfmt_aout.c et al. We inherit
    EXTRA_REGS from the prior executable.

This inconsistency was not intended.

This change removes SAVE/RESTORE_EXTRA_REGS in stub_execve,
removes register clearing in ELF_PLAT_INIT(),
and instead simply clears them on success in stub_execve.

Run-tested.

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Alexei Starovoitov <ast@plumgrid.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Will Drewry <wad@chromium.org>
Link: http://lkml.kernel.org/r/1428173719-7637-1-git-send-email-dvlasenk@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2015-04-06 09:24:08 +02:00

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/*
x86 function call convention, 64-bit:
-------------------------------------
arguments | callee-saved | extra caller-saved | return
[callee-clobbered] | | [callee-clobbered] |
---------------------------------------------------------------------------
rdi rsi rdx rcx r8-9 | rbx rbp [*] r12-15 | r10-11 | rax, rdx [**]
( rsp is obviously invariant across normal function calls. (gcc can 'merge'
functions when it sees tail-call optimization possibilities) rflags is
clobbered. Leftover arguments are passed over the stack frame.)
[*] In the frame-pointers case rbp is fixed to the stack frame.
[**] for struct return values wider than 64 bits the return convention is a
bit more complex: up to 128 bits width we return small structures
straight in rax, rdx. For structures larger than that (3 words or
larger) the caller puts a pointer to an on-stack return struct
[allocated in the caller's stack frame] into the first argument - i.e.
into rdi. All other arguments shift up by one in this case.
Fortunately this case is rare in the kernel.
For 32-bit we have the following conventions - kernel is built with
-mregparm=3 and -freg-struct-return:
x86 function calling convention, 32-bit:
----------------------------------------
arguments | callee-saved | extra caller-saved | return
[callee-clobbered] | | [callee-clobbered] |
-------------------------------------------------------------------------
eax edx ecx | ebx edi esi ebp [*] | <none> | eax, edx [**]
( here too esp is obviously invariant across normal function calls. eflags
is clobbered. Leftover arguments are passed over the stack frame. )
[*] In the frame-pointers case ebp is fixed to the stack frame.
[**] We build with -freg-struct-return, which on 32-bit means similar
semantics as on 64-bit: edx can be used for a second return value
(i.e. covering integer and structure sizes up to 64 bits) - after that
it gets more complex and more expensive: 3-word or larger struct returns
get done in the caller's frame and the pointer to the return struct goes
into regparm0, i.e. eax - the other arguments shift up and the
function's register parameters degenerate to regparm=2 in essence.
*/
#include <asm/dwarf2.h>
#ifdef CONFIG_X86_64
/*
* 64-bit system call stack frame layout defines and helpers,
* for assembly code:
*/
/* The layout forms the "struct pt_regs" on the stack: */
/*
* C ABI says these regs are callee-preserved. They aren't saved on kernel entry
* unless syscall needs a complete, fully filled "struct pt_regs".
*/
#define R15 0*8
#define R14 1*8
#define R13 2*8
#define R12 3*8
#define RBP 4*8
#define RBX 5*8
/* These regs are callee-clobbered. Always saved on kernel entry. */
#define R11 6*8
#define R10 7*8
#define R9 8*8
#define R8 9*8
#define RAX 10*8
#define RCX 11*8
#define RDX 12*8
#define RSI 13*8
#define RDI 14*8
/*
* On syscall entry, this is syscall#. On CPU exception, this is error code.
* On hw interrupt, it's IRQ number:
*/
#define ORIG_RAX 15*8
/* Return frame for iretq */
#define RIP 16*8
#define CS 17*8
#define EFLAGS 18*8
#define RSP 19*8
#define SS 20*8
#define SIZEOF_PTREGS 21*8
.macro ALLOC_PT_GPREGS_ON_STACK addskip=0
subq $15*8+\addskip, %rsp
CFI_ADJUST_CFA_OFFSET 15*8+\addskip
.endm
.macro SAVE_C_REGS_HELPER offset=0 rax=1 rcx=1 r8910=1 r11=1
.if \r11
movq_cfi r11, 6*8+\offset
.endif
.if \r8910
movq_cfi r10, 7*8+\offset
movq_cfi r9, 8*8+\offset
movq_cfi r8, 9*8+\offset
.endif
.if \rax
movq_cfi rax, 10*8+\offset
.endif
.if \rcx
movq_cfi rcx, 11*8+\offset
.endif
movq_cfi rdx, 12*8+\offset
movq_cfi rsi, 13*8+\offset
movq_cfi rdi, 14*8+\offset
.endm
.macro SAVE_C_REGS offset=0
SAVE_C_REGS_HELPER \offset, 1, 1, 1, 1
.endm
.macro SAVE_C_REGS_EXCEPT_RAX_RCX offset=0
SAVE_C_REGS_HELPER \offset, 0, 0, 1, 1
.endm
.macro SAVE_C_REGS_EXCEPT_R891011
SAVE_C_REGS_HELPER 0, 1, 1, 0, 0
.endm
.macro SAVE_C_REGS_EXCEPT_RCX_R891011
SAVE_C_REGS_HELPER 0, 1, 0, 0, 0
.endm
.macro SAVE_C_REGS_EXCEPT_RAX_RCX_R11
SAVE_C_REGS_HELPER 0, 0, 0, 1, 0
.endm
.macro SAVE_EXTRA_REGS offset=0
movq_cfi r15, 0*8+\offset
movq_cfi r14, 1*8+\offset
movq_cfi r13, 2*8+\offset
movq_cfi r12, 3*8+\offset
movq_cfi rbp, 4*8+\offset
movq_cfi rbx, 5*8+\offset
.endm
.macro SAVE_EXTRA_REGS_RBP offset=0
movq_cfi rbp, 4*8+\offset
.endm
.macro RESTORE_EXTRA_REGS offset=0
movq_cfi_restore 0*8+\offset, r15
movq_cfi_restore 1*8+\offset, r14
movq_cfi_restore 2*8+\offset, r13
movq_cfi_restore 3*8+\offset, r12
movq_cfi_restore 4*8+\offset, rbp
movq_cfi_restore 5*8+\offset, rbx
.endm
.macro ZERO_EXTRA_REGS
xorl %r15d, %r15d
xorl %r14d, %r14d
xorl %r13d, %r13d
xorl %r12d, %r12d
xorl %ebp, %ebp
xorl %ebx, %ebx
.endm
.macro RESTORE_C_REGS_HELPER rstor_rax=1, rstor_rcx=1, rstor_r11=1, rstor_r8910=1, rstor_rdx=1
.if \rstor_r11
movq_cfi_restore 6*8, r11
.endif
.if \rstor_r8910
movq_cfi_restore 7*8, r10
movq_cfi_restore 8*8, r9
movq_cfi_restore 9*8, r8
.endif
.if \rstor_rax
movq_cfi_restore 10*8, rax
.endif
.if \rstor_rcx
movq_cfi_restore 11*8, rcx
.endif
.if \rstor_rdx
movq_cfi_restore 12*8, rdx
.endif
movq_cfi_restore 13*8, rsi
movq_cfi_restore 14*8, rdi
.endm
.macro RESTORE_C_REGS
RESTORE_C_REGS_HELPER 1,1,1,1,1
.endm
.macro RESTORE_C_REGS_EXCEPT_RAX
RESTORE_C_REGS_HELPER 0,1,1,1,1
.endm
.macro RESTORE_C_REGS_EXCEPT_RCX
RESTORE_C_REGS_HELPER 1,0,1,1,1
.endm
.macro RESTORE_C_REGS_EXCEPT_R11
RESTORE_C_REGS_HELPER 1,1,0,1,1
.endm
.macro RESTORE_C_REGS_EXCEPT_RCX_R11
RESTORE_C_REGS_HELPER 1,0,0,1,1
.endm
.macro RESTORE_RSI_RDI
RESTORE_C_REGS_HELPER 0,0,0,0,0
.endm
.macro RESTORE_RSI_RDI_RDX
RESTORE_C_REGS_HELPER 0,0,0,0,1
.endm
.macro REMOVE_PT_GPREGS_FROM_STACK addskip=0
addq $15*8+\addskip, %rsp
CFI_ADJUST_CFA_OFFSET -(15*8+\addskip)
.endm
.macro icebp
.byte 0xf1
.endm
#else /* CONFIG_X86_64 */
/*
* For 32bit only simplified versions of SAVE_ALL/RESTORE_ALL. These
* are different from the entry_32.S versions in not changing the segment
* registers. So only suitable for in kernel use, not when transitioning
* from or to user space. The resulting stack frame is not a standard
* pt_regs frame. The main use case is calling C code from assembler
* when all the registers need to be preserved.
*/
.macro SAVE_ALL
pushl_cfi_reg eax
pushl_cfi_reg ebp
pushl_cfi_reg edi
pushl_cfi_reg esi
pushl_cfi_reg edx
pushl_cfi_reg ecx
pushl_cfi_reg ebx
.endm
.macro RESTORE_ALL
popl_cfi_reg ebx
popl_cfi_reg ecx
popl_cfi_reg edx
popl_cfi_reg esi
popl_cfi_reg edi
popl_cfi_reg ebp
popl_cfi_reg eax
.endm
#endif /* CONFIG_X86_64 */
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