From: Denys Vlasenko <[email protected]>
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 <[email protected]>
Acked-by: Andy Lutomirski <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Brian Gerst <[email protected]>
Cc: Frederic Weisbecker <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Steven Rostedt <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Will Drewry <[email protected]>
Cc: [email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>
Signed-off-by: Srivatsa S. Bhat <[email protected]>
Reviewed-by: Matt Helsley (VMware) <[email protected]>
Reviewed-by: Alexey Makhalov <[email protected]>
Reviewed-by: Bo Gan <[email protected]>
---
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 */