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 11:43, <feng.wu@xxxxxxxxx> wrote:

> 
>> -----Original Message-----
>> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
>> Sent: Monday, April 28, 2014 5:26 PM
>> To: Wu, Feng
>> Cc: andrew.cooper3@xxxxxxxxxx; ian.campbell@xxxxxxxxxx; Dong, Eddie;
>> Nakajima, Jun; Tian, Kevin; xen-devel@xxxxxxxxxxxxx 
>> Subject: Re: [PATCH v3 4/9] Clear AC bit in RFLAGS to protect Xen itself by 
> SMAP
>> 
>> >>> 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?
> 
> Most of them can be moved into SAVE_ALL obviously, however, there are two 
> exceptions:
> 
> 1. SAVE_ALL is not executed in the beginning of some exception handlers, 
> such as, double_fault, nmi, etc. 

But that's orthogonal - I didn't say that would automatically cover
_all_ cases.

> 2. We don't need CLAC in .fixup section where SAVE_ALL is used.

Do we not?

Jan



_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel