diff options
| author | Denys Vlasenko <dvlasenk@redhat.com> | 2015-03-27 11:36:21 +0100 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2015-03-27 12:27:57 +0100 |
| commit | 4ee8ec17ba00fce4af042543771f996fb9d98d34 (patch) | |
| tree | 768bd1721024814da059c730d9dc0f6f796d16a7 /arch/x86/ia32 | |
| parent | a232e3d558eef421fbb539ede5483dfb668e38f2 (diff) | |
x86/asm/entry/32: Make register zero-extension more prominent
There are a couple of syscall argument zero-extension instructions in
the 32-bit compat entry code, and it was mentioned that people keep
trying to optimize them out, introducing bugs.
Make them more visible, and add a "do not remove" comment.
Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Alexei Starovoitov <ast@plumgrid.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
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: Oleg Nesterov <oleg@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Will Drewry <wad@chromium.org>
Link: http://lkml.kernel.org/r/1427452582-21624-3-git-send-email-dvlasenk@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'arch/x86/ia32')
| -rw-r--r-- | arch/x86/ia32/ia32entry.S | 14 |
1 files changed, 10 insertions, 4 deletions
diff --git a/arch/x86/ia32/ia32entry.S b/arch/x86/ia32/ia32entry.S index 7502ff0b938e..dec8c1de9c9e 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. |