Re: [Xen-devel] [PATCH 1/2] x86/hvm: Always do SMAP check when updating runstate_guest(v)

[Tim Deegan <tim@xxxxxxx>]

At 13:11 +0100 on 23 Jul (1406117492), Jan Beulich wrote:
> >>> On 10.07.14 at 12:56, <tim@xxxxxxx> wrote:
> > At 07:18 +0800 on 08 Jul (1404800297), Feng Wu wrote:
> >> In the current implementation, we honor the guest's CPL and AC
> >> to determain whether do the SMAP check or not for runstate_guest(v).
> >> However, this doesn't work. The VMCS feild is invalid when we try
> >> to get geust's SS by hvm_get_segment_register(), since the
> >> right VMCS has not beed loaded for the current VCPU.
> >> 
> >> In this patch, we always do the SMAP check when updating
> >> runstate_guest(v) for the guest when SMAP is enabled by it.
> > 
> > Surely the correct behaviour is _not_ to do the check -- this is the
> > context switch path in the _hypervisor_, not a guest-kernel operation.
> 
> But it is being "asked for" by the kernel, and hence should be treated
> as implicit supervisor mode access just like e.g. descriptor table
> accesses (see also the earlier discussion in the thread where the problem
> got reported).

OK, that makes sense.

Tim.

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