It was mentioned that people keep trying to optimize them out,
introducing bugs. Make them more visible, and add "do not remove"
comment.
Signed-off-by: Denys Vlasenko <dvlas...@redhat.com>
CC: Linus Torvalds <torva...@linux-foundation.org>
CC: Steven Rostedt <rost...@goodmis.org>
CC: Ingo Molnar <mi...@kernel.org>
CC: Borislav Petkov <b...@alien8.de>
CC: "H. Peter Anvin" <h...@zytor.com>
CC: Andy Lutomirski <l...@amacapital.net>
CC: Oleg Nesterov <o...@redhat.com>
CC: Frederic Weisbecker <fweis...@gmail.com>
CC: Alexei Starovoitov <a...@plumgrid.com>
CC: Will Drewry <w...@chromium.org>
CC: Kees Cook <keesc...@chromium.org>
CC: x...@kernel.org
CC: linux-kernel@vger.kernel.org
---
arch/x86/ia32/ia32entry.S | 14 ++++++++++----
1 file changed, 10 insertions(+), 4 deletions(-)
diff --git a/arch/x86/ia32/ia32entry.S b/arch/x86/ia32/ia32entry.S
index 7502ff0..dec8c1d 100644
--- a/arch/x86/ia32/ia32entry.S
+++ b/arch/x86/ia32/ia32entry.S
@@ -122,8 +122,11 @@ ENTRY(ia32_sysenter_target)
movq PER_CPU_VAR(cpu_tss + TSS_sp0), %rsp
ENABLE_INTERRUPTS(CLBR_NONE)
+ /* Zero-extending 32-bit regs, do not remove */
+ movl %ebp, %ebp
+ movl %eax, %eax
+
/* Construct iret frame (ss,rsp,rflags,cs,rip) */
- movl %ebp,%ebp /* zero extension */
pushq_cfi $__USER32_DS
/*CFI_REL_OFFSET ss,0*/
pushq_cfi %rbp
@@ -134,7 +137,6 @@ ENTRY(ia32_sysenter_target)
CFI_REGISTER rip,r10
pushq_cfi $__USER32_CS
/*CFI_REL_OFFSET cs,0*/
- movl %eax, %eax
/* Store thread_info->sysenter_return in rip stack slot */
pushq_cfi %r10
CFI_REL_OFFSET rip,0
@@ -329,9 +331,11 @@ ENTRY(ia32_cstar_target)
movq PER_CPU_VAR(kernel_stack),%rsp
ENABLE_INTERRUPTS(CLBR_NONE)
+ /* Zero-extending 32-bit regs, do not remove */
+ movl %eax,%eax
+
ALLOC_PT_GPREGS_ON_STACK 6*8 /* 6*8: space for orig_ax and iret frame */
SAVE_C_REGS_EXCEPT_RCX_R891011
- movl %eax,%eax /* zero extension */
movq %rax,ORIG_RAX(%rsp)
movq %rcx,RIP(%rsp)
CFI_REL_OFFSET rip,RIP
@@ -471,7 +475,9 @@ ENTRY(ia32_syscall)
SWAPGS
ENABLE_INTERRUPTS(CLBR_NONE)
- movl %eax,%eax
+ /* Zero-extending 32-bit regs, do not remove */
+ movl %eax,%eax
+
pushq_cfi %rax /* store orig_ax */
cld
/* note the registers are not zero extended to the sf.
--
1.8.1.4
--
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