lkml.org 
[lkml]   [2018]   [Jul]   [14]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Subject[PATCH 4.4.y 033/101] x86/asm/entry/32: Simplify pushes of zeroed pt_regs->REGs
From
Date
From: Denys Vlasenko <dvlasenk@redhat.com>

commit 778843f934e362ed4ed734520f60a44a78a074b4 upstream

Use of a temporary R8 register here seems to be unnecessary.

"push %r8" is a two-byte insn (it needs REX prefix to specify R8),
"push $0" is two-byte too. It seems just using the latter would be
no worse.

Thus, code had an unnecessary "xorq %r8,%r8" insn.
It probably costs nothing in execution time here since we are probably
limited by store bandwidth at this point, but still.

Run-tested under QEMU: 32-bit calls still work:

/ # ./test_syscall_vdso32
[RUN] Executing 6-argument 32-bit syscall via VDSO
[OK] Arguments are preserved across syscall
[NOTE] R11 has changed:0000000000200ed7 - assuming clobbered by SYSRET insn
[OK] R8..R15 did not leak kernel data
[RUN] Executing 6-argument 32-bit syscall via INT 80
[OK] Arguments are preserved across syscall
[OK] R8..R15 did not leak kernel data
[RUN] Running tests under ptrace
[RUN] Executing 6-argument 32-bit syscall via VDSO
[OK] Arguments are preserved across syscall
[NOTE] R11 has changed:0000000000200ed7 - assuming clobbered by SYSRET insn
[OK] R8..R15 did not leak kernel data
[RUN] Executing 6-argument 32-bit syscall via INT 80
[OK] Arguments are preserved across syscall
[OK] R8..R15 did not leak kernel data

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
Acked-by: Andy Lutomirski <luto@kernel.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: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Drewry <wad@chromium.org>
Cc: linux-kernel@vger.kernel.org
Link: http://lkml.kernel.org/r/1462201010-16846-1-git-send-email-dvlasenk@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Srivatsa S. Bhat <srivatsa@csail.mit.edu>
Reviewed-by: Matt Helsley (VMware) <matt.helsley@gmail.com>
Reviewed-by: Alexey Makhalov <amakhalov@vmware.com>
Reviewed-by: Bo Gan <ganb@vmware.com>
---

arch/x86/entry/entry_64_compat.S | 45 ++++++++++++++++++--------------------
1 file changed, 21 insertions(+), 24 deletions(-)

diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S
index d03bf0e..e479ff8 100644
--- a/arch/x86/entry/entry_64_compat.S
+++ b/arch/x86/entry/entry_64_compat.S
@@ -79,24 +79,23 @@ ENTRY(entry_SYSENTER_compat)
ASM_CLAC /* Clear AC after saving FLAGS */

pushq $__USER32_CS /* pt_regs->cs */
- xorq %r8,%r8
- pushq %r8 /* pt_regs->ip = 0 (placeholder) */
+ pushq $0 /* pt_regs->ip = 0 (placeholder) */
pushq %rax /* pt_regs->orig_ax */
pushq %rdi /* pt_regs->di */
pushq %rsi /* pt_regs->si */
pushq %rdx /* pt_regs->dx */
pushq %rcx /* pt_regs->cx */
pushq $-ENOSYS /* pt_regs->ax */
- pushq %r8 /* pt_regs->r8 = 0 */
- pushq %r8 /* pt_regs->r9 = 0 */
- pushq %r8 /* pt_regs->r10 = 0 */
- pushq %r8 /* pt_regs->r11 = 0 */
+ pushq $0 /* pt_regs->r8 = 0 */
+ pushq $0 /* pt_regs->r9 = 0 */
+ pushq $0 /* pt_regs->r10 = 0 */
+ pushq $0 /* pt_regs->r11 = 0 */
pushq %rbx /* pt_regs->rbx */
pushq %rbp /* pt_regs->rbp (will be overwritten) */
- pushq %r8 /* pt_regs->r12 = 0 */
- pushq %r8 /* pt_regs->r13 = 0 */
- pushq %r8 /* pt_regs->r14 = 0 */
- pushq %r8 /* pt_regs->r15 = 0 */
+ pushq $0 /* pt_regs->r12 = 0 */
+ pushq $0 /* pt_regs->r13 = 0 */
+ pushq $0 /* pt_regs->r14 = 0 */
+ pushq $0 /* pt_regs->r15 = 0 */
cld

/*
@@ -185,17 +184,16 @@ ENTRY(entry_SYSCALL_compat)
pushq %rdx /* pt_regs->dx */
pushq %rbp /* pt_regs->cx (stashed in bp) */
pushq $-ENOSYS /* pt_regs->ax */
- xorq %r8,%r8
- pushq %r8 /* pt_regs->r8 = 0 */
- pushq %r8 /* pt_regs->r9 = 0 */
- pushq %r8 /* pt_regs->r10 = 0 */
- pushq %r8 /* pt_regs->r11 = 0 */
+ pushq $0 /* pt_regs->r8 = 0 */
+ pushq $0 /* pt_regs->r9 = 0 */
+ pushq $0 /* pt_regs->r10 = 0 */
+ pushq $0 /* pt_regs->r11 = 0 */
pushq %rbx /* pt_regs->rbx */
pushq %rbp /* pt_regs->rbp (will be overwritten) */
- pushq %r8 /* pt_regs->r12 = 0 */
- pushq %r8 /* pt_regs->r13 = 0 */
- pushq %r8 /* pt_regs->r14 = 0 */
- pushq %r8 /* pt_regs->r15 = 0 */
+ pushq $0 /* pt_regs->r12 = 0 */
+ pushq $0 /* pt_regs->r13 = 0 */
+ pushq $0 /* pt_regs->r14 = 0 */
+ pushq $0 /* pt_regs->r15 = 0 */

/*
* User mode is traced as though IRQs are on, and SYSENTER
@@ -292,11 +290,10 @@ ENTRY(entry_INT80_compat)
pushq %rdx /* pt_regs->dx */
pushq %rcx /* pt_regs->cx */
pushq $-ENOSYS /* pt_regs->ax */
- xorq %r8,%r8
- pushq %r8 /* pt_regs->r8 = 0 */
- pushq %r8 /* pt_regs->r9 = 0 */
- pushq %r8 /* pt_regs->r10 = 0 */
- pushq %r8 /* pt_regs->r11 = 0 */
+ pushq $0 /* pt_regs->r8 = 0 */
+ pushq $0 /* pt_regs->r9 = 0 */
+ pushq $0 /* pt_regs->r10 = 0 */
+ pushq $0 /* pt_regs->r11 = 0 */
pushq %rbx /* pt_regs->rbx */
pushq %rbp /* pt_regs->rbp */
pushq %r12 /* pt_regs->r12 */
\
 
 \ /
  Last update: 2018-07-15 22:07    [W:0.056 / U:0.076 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site