Commit fc3e958a authored by Denys Vlasenko's avatar Denys Vlasenko Committed by Ingo Molnar
Browse files

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: default avatarDenys 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: default avatarIngo Molnar <mingo@kernel.org>
parent 6a3713f0

arch/x86/include/asm/calling.h

+9 −0
Original line number Diff line number Diff line
@@ -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

arch/x86/include/asm/elf.h

+4 −3
Original line number Diff line number Diff line
@@ -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;

arch/x86/kernel/entry_64.S

+22 −28
Original line number Diff line number Diff line
@@ -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)

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