Re: [Xen-devel] Ping: [PATCH 2/5] x86emul: limit-check branch targets

[Tim Deegan <tim@xxxxxxx>]

At 07:52 -0700 on 25 Feb (1456386721), Jan Beulich wrote:
> >>> On 17.02.16 at 17:35, <JBeulich@xxxxxxxx> wrote:
> > All branches need to #GP when their target violates the segment limit
> > (in 16- and 32-bit modes) or is non-canonical (in 64-bit mode). For
> > near branches facilitate this via a zero-byte instruction fetch from
> > the target address (resulting in address translation and validation
> > without an actual read from memory), while far branches get dealt with
> > by breaking up the segment register loading into a read-and-validate
> > part and a write one. The latter at once allows correcting some
> > ordering issues in how the individual emulation steps get carried out:
> > Before updating machine state, all exceptions unrelated to that state
> > updating should have got raised (i.e. the only ones possibly resulting
> > in partly updated state are faulting memory writes [pushes]).
> > 
> > Note that while not immediately needed here, write and distinct read
> > emulation routines get updated to deal with zero byte accesses too, for
> > overall consistency.
> > 
> > Reported-by: å??令 <liuling-it@xxxxxx>
> > Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

Sorry, hadn't spotted the shadow change.

Acked-by: Tim Deegan <tim@xxxxxxx>

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