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

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 17/02/16 16:35, Jan Beulich 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: ÃËËÃÂÂ <liuling-it@xxxxxx>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

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