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Re: [PATCH] x86emul: V{,P}{COMPRESS,EXPAND}* can (wrongly) trigger assertion
- To: Jan Beulich <jbeulich@xxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Thu, 16 Jul 2026 11:44:59 +0100
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Teddy Astie <teddy.astie@xxxxxxxxxx>
- Delivery-date: Thu, 16 Jul 2026 10:45:16 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 16/07/2026 11:43 am, Jan Beulich wrote:
> AFL has pointed out that the op_bytes-is-not-0 assertion in common SIMD
> handling can trigger for these insns. Indeed when the (relevant part of)
> the controlling mask register is 0, no memory is accessed at all. Leave
> op_bytes unaltered in this case, to engage the short-circuiting in common
> SIMD handling when fault_suppression is true and op_bytes is 0.
>
> While there also correct a related typo in the test harness.
>
> Fixes: 65f82d4ce1ea ("x86emul: support AVX512{F,_VBMI2} compress/expand
> insns")
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
Acked-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Is this local AFL testing? I'm slightly surprised that OSS-Fuzz hasn't
found this.
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