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Commit 61b1e3e7 authored by Denys Vlasenko's avatar Denys Vlasenko Committed by Ingo Molnar
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x86/asm/entry/32: Simplify the zeroing of pt_regs->r8..r11 in the int80 code path 



32-bit syscall entry points do not save the complete pt_regs struct,
they leave some fields uninitialized. However, they must be
careful to not leak uninitialized data in pt_regs->r8..r11 to
ptrace users.

CLEAR_RREGS macro is used to zero these fields out when needed.

However, in the int80 code path this zeroing is unconditional.
This patch simplifies it by storing zeroes there right away,
when pt_regs is constructed on stack.

This uses shorter instructions:

   text    data     bss     dec     hex filename
   1423       0       0    1423     58f ia32entry.o.before
   1407       0       0    1407     57f ia32entry.o

Compile-tested.

Signed-off-by: default avatarDenys Vlasenko <dvlasenk@redhat.com>
Cc: Alexei Starovoitov <ast@plumgrid.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
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: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Drewry <wad@chromium.org>
Link: http://lkml.kernel.org/r/1433266510-2938-1-git-send-email-dvlasenk@redhat.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 5ca6f70f

arch/x86/entry/ia32entry.S

+9 −4
Original line number Diff line number Diff line
@@ -421,6 +421,10 @@ ia32_badarg: 
	movq $-EFAULT,%rax

	jmp ia32_sysret



ia32_ret_from_sys_call:

	CLEAR_RREGS

	jmp int_ret_from_sys_call



/*

 * Emulated IA32 system calls via int 0x80.

 *
@@ -462,8 +466,12 @@ ENTRY(ia32_syscall) 
	pushq	%rdx			/* pt_regs->dx */

	pushq	%rcx			/* pt_regs->cx */

	pushq	$-ENOSYS		/* pt_regs->ax */

	pushq	$0			/* pt_regs->r8 */

	pushq	$0			/* pt_regs->r9 */

	pushq	$0			/* pt_regs->r10 */

	pushq	$0			/* pt_regs->r11 */

	cld

	sub	$(10*8),%rsp /* pt_regs->r8-11,bp,bx,r12-15 not saved */

	sub	$(6*8),%rsp /* pt_regs->bp,bx,r12-15 not saved */



	orl $TS_COMPAT, ASM_THREAD_INFO(TI_status, %rsp, SIZEOF_PTREGS)

	testl $_TIF_WORK_SYSCALL_ENTRY, ASM_THREAD_INFO(TI_flags, %rsp, SIZEOF_PTREGS)
@@ -481,13 +489,10 @@ ia32_do_call: 
ia32_sysret:

	movq %rax,RAX(%rsp)

1:

ia32_ret_from_sys_call:

	CLEAR_RREGS

	jmp int_ret_from_sys_call



ia32_tracesys:

	SAVE_EXTRA_REGS

	CLEAR_RREGS

	movq %rsp,%rdi        /* &pt_regs -> arg1 */

	call syscall_trace_enter

	LOAD_ARGS32	/* reload args from stack in case ptrace changed it */