Re: [Xen-devel] [PATCH v2 2/7] Clear AC bit in RFLAGS to protect Xen itself by SMAP

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 23.04.14 at 16:35, <feng.wu@xxxxxxxxx> wrote:
> --- a/xen/arch/x86/x86_64/entry.S
> +++ b/xen/arch/x86/x86_64/entry.S
> @@ -120,6 +120,7 @@ restore_all_xen:
>   * the space left by the trampoline.
>   */
>  ENTRY(syscall_enter)
> +        ASM_CLAC

This should be avoidable by instead adjusting the value written to
MSR_SYSCALL_MASK.

> @@ -476,6 +479,7 @@ ENTRY(ret_from_intr)
>          jmp   compat_test_all_events
>  
>  ENTRY(page_fault)
> +        ASM_CLAC
>          movl  $TRAP_page_fault,4(%rsp)
>  /* No special register assumptions. */
>  GLOBAL(handle_exception)

Considering that ASM_CLAC already contains a memory access (which
hence isn't guarded) I wonder whether this wouldn't better be moved
into handle_exception at least for now (reducing code redundancy).

Jan


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