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 | "Srivatsa S. Bhat" <> | Date | Sat, 14 Jul 2018 02:30:46 -0700 |
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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 */
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