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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>
This commit is contained in:
Denys Vlasenko 2015-04-04 20:55:19 +02:00 committed by Ingo Molnar
parent 6a3713f001
commit fc3e958a2b
3 changed files with 35 additions and 31 deletions
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9
arch/x86/include/asm/calling.h
View File

@ -151,6 +151,15 @@ For 32-bit we have the following conventions - kernel is built with
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

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

@ -171,10 +171,11 @@ do { \
static inline void elf_common_init(struct thread_struct *t,
struct pt_regs *regs, const u16 ds)
{
regs->ax = regs->bx = regs->cx = regs->dx = 0;
regs->si = regs->di = regs->bp = 0;
/* Commented-out registers are cleared in stub_execve */
/*regs->ax = regs->bx =*/ regs->cx = regs->dx = 0;
regs->si = regs->di /*= regs->bp*/ = 0;
regs->r8 = regs->r9 = regs->r10 = regs->r11 = 0;
regs->r12 = regs->r13 = regs->r14 = regs->r15 = 0;
/*regs->r12 = regs->r13 = regs->r14 = regs->r15 = 0;*/
t->fs = t->gs = 0;
t->fsindex = t->gsindex = 0;
t->ds = t->es = ds;

38
arch/x86/kernel/entry_64.S
View File

@ -419,25 +419,27 @@ END(stub_\func)
ENTRY(stub_execve)
CFI_STARTPROC
addq $8, %rsp
DEFAULT_FRAME 0
SAVE_EXTRA_REGS
DEFAULT_FRAME 0, 8
call sys_execve
return_from_execve:
testl %eax, %eax
jz 1f
/* exec failed, can use fast SYSRET code path in this case */
ret
1:
/* must use IRET code path (pt_regs->cs may have changed) */
addq $8, %rsp
ZERO_EXTRA_REGS
movq %rax,RAX(%rsp)
RESTORE_EXTRA_REGS
jmp int_ret_from_sys_call
CFI_ENDPROC
END(stub_execve)
ENTRY(stub_execveat)
CFI_STARTPROC
addq $8, %rsp
DEFAULT_FRAME 0
SAVE_EXTRA_REGS
DEFAULT_FRAME 0, 8
call sys_execveat
movq %rax,RAX(%rsp)
RESTORE_EXTRA_REGS
jmp int_ret_from_sys_call
jmp return_from_execve
CFI_ENDPROC
END(stub_execveat)
@ -472,25 +474,17 @@ END(stub_x32_rt_sigreturn)
ENTRY(stub_x32_execve)
CFI_STARTPROC
addq $8, %rsp
DEFAULT_FRAME 0
SAVE_EXTRA_REGS
DEFAULT_FRAME 0, 8
call compat_sys_execve
movq %rax,RAX(%rsp)
RESTORE_EXTRA_REGS
jmp int_ret_from_sys_call
jmp return_from_execve
CFI_ENDPROC
END(stub_x32_execve)
ENTRY(stub_x32_execveat)
CFI_STARTPROC
addq $8, %rsp
DEFAULT_FRAME 0
SAVE_EXTRA_REGS
DEFAULT_FRAME 0, 8
call compat_sys_execveat
movq %rax,RAX(%rsp)
RESTORE_EXTRA_REGS
jmp int_ret_from_sys_call
jmp return_from_execve
CFI_ENDPROC
END(stub_x32_execveat)