Commit-ID: 4ee8ec17ba00fce4af042543771f996fb9d98d34 Gitweb: http://git.kernel.org/tip/4ee8ec17ba00fce4af042543771f996fb9d98d34 Author: Denys Vlasenko <dvlasenk@xxxxxxxxxx> AuthorDate: Fri, 27 Mar 2015 11:36:21 +0100 Committer: Ingo Molnar <mingo@xxxxxxxxxx> CommitDate: Fri, 27 Mar 2015 12:27:57 +0100 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@xxxxxxxxxx> Cc: Alexei Starovoitov <ast@xxxxxxxxxxxx> Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx> Cc: Borislav Petkov <bp@xxxxxxxxx> Cc: Frederic Weisbecker <fweisbec@xxxxxxxxx> Cc: H. Peter Anvin <hpa@xxxxxxxxx> Cc: Kees Cook <keescook@xxxxxxxxxxxx> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Cc: Oleg Nesterov <oleg@xxxxxxxxxx> Cc: Steven Rostedt <rostedt@xxxxxxxxxxx> Cc: Will Drewry <wad@xxxxxxxxxxxx> Link: http://lkml.kernel.org/r/1427452582-21624-3-git-send-email-dvlasenk@xxxxxxxxxx Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx> --- 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. -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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