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Re: [PATCH] x86/PV: use 64-bit subtract to adjust guest RIP upon missing SYSCALL callbacks
- To: Jan Beulich <jbeulich@xxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Tue, 26 Jan 2021 16:57:25 +0000
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On 26/01/2021 16:31, Jan Beulich wrote:
> When discussing the shrunk down version of the commit in question it
> was said (in reply to my conditional choosing of the width):
>
> "However, the 32bit case isn't actually interesting here. A
> guest can't execute a SYSCALL instruction on/across the 4G->0 boundary
> because the M2P is mapped NX up to the 4G boundary, so we can never
> reach this point with %eip < 2.
>
> Therefore, the 64bit-only form is the appropriate one to use, which
> solves any question of cleverness, or potential decode stalls it
> causes."
>
> Fixes: ca6fcf4321b3 ("x86/pv: Inject #UD for missing SYSCALL callbacks")
> Signed-off-by: Jan Beulich <JBeulich@xxxxxxxx>
Crap. I folded the fix into my wrong tree. Sorry.
Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
~Andrew
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