From 778843f934e362ed4ed734520f60a44a78a074b4 Mon Sep 17 00:00:00 2001 From: Denys Vlasenko Date: Mon, 2 May 2016 16:56:50 +0200 Subject: [PATCH] x86/asm/entry/32: Simplify pushes of zeroed pt_regs->REGs 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 Acked-by: Andy Lutomirski Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Brian Gerst Cc: Frederic Weisbecker Cc: H. Peter Anvin Cc: Kees Cook Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Steven Rostedt Cc: Thomas Gleixner Cc: Will Drewry 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 --- 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 847f2f0c31e5..e1721dafbcb1 100644 --- a/arch/x86/entry/entry_64_compat.S +++ b/arch/x86/entry/entry_64_compat.S @@ -72,24 +72,23 @@ ENTRY(entry_SYSENTER_compat) pushfq /* pt_regs->flags (except IF = 0) */ orl $X86_EFLAGS_IF, (%rsp) /* Fix saved 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 /* @@ -205,17 +204,16 @@ 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 @@ -316,11 +314,10 @@ 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 */ -- 2.20.1