Re: [Xen-devel] [PATCH v3 4/9] Clear AC bit in RFLAGS to protect Xen itself by SMAP

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 28.04.14 at 05:15, <feng.wu@xxxxxxxxx> wrote:
> @@ -466,6 +468,7 @@ ENTRY(dom_crash_sync_extable)
>          jmp   asm_domain_crash_synchronous /* Does not return */
>  
>  ENTRY(common_interrupt)
> +        ASM_CLAC
>          SAVE_ALL
>          movq %rsp,%rdi
>          callq do_IRQ
> @@ -485,6 +488,7 @@ ENTRY(page_fault)
>          movl  $TRAP_page_fault,4(%rsp)
>  /* No special register assumptions. */
>  GLOBAL(handle_exception)
> +        ASM_CLAC
>          SAVE_ALL

Did you check whether the addition wouldn't better go right into
SAVE_ALL?

> --- a/xen/arch/x86/x86_64/traps.c
> +++ b/xen/arch/x86/x86_64/traps.c
> @@ -437,8 +437,8 @@ void __devinit subarch_percpu_traps_init(void)
>      /* Common SYSCALL parameters. */
>      wrmsr(MSR_STAR, 0, (FLAT_RING3_CS32<<16) | __HYPERVISOR_CS);
>      wrmsr(MSR_SYSCALL_MASK,
> -          X86_EFLAGS_VM|X86_EFLAGS_RF|X86_EFLAGS_NT|
> -          X86_EFLAGS_DF|X86_EFLAGS_IF|X86_EFLAGS_TF,
> +          X86_EFLAGS_VM|X86_EFLAGS_RF|X86_EFLAGS_NT|X86_EFLAGS_DF|
> +          X86_EFLAGS_IF|X86_EFLAGS_TF|X86_EFLAGS_AC,

Please pay attention to ordering of existing accumulations like this:
Here, the operands are ordered by bit position, so the addition
should go at the beginning of the expression rather than the end.

Jan


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