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Re: [PATCH] x86emul: fix UB multiplications in S/G handling
- To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Tue, 13 Aug 2024 17:19:00 +0200
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- Cc: Roger Pau Monné <roger.pau@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Tue, 13 Aug 2024 15:19:07 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 13.08.2024 17:16, Andrew Cooper wrote:
> On 13/08/2024 2:19 pm, Andrew Cooper wrote:
>> On 13/08/2024 1:43 pm, Jan Beulich wrote:
>>> The conversion of the shifts to multiplications by the commits tagged
>>> below still wasn't quite right: The multiplications (of signed values)
>>> can overflow, too. As of 298556c7b5f8 ("x86emul: correct 32-bit address
>>> handling for AVX2 gathers") signed multiplication wasn't necessary
>>> anymore, though: The necessary sign-extension (if any) will happen as
>>> well when using intermediate variables of unsigned long types, and
>>> excess address bits are chopped off by truncate_ea().
>>>
>>> Fixes: b6a907f8c83d ("x86emul: replace UB shifts")
>>> Fixes: 21de9680eb59 ("x86emul: replace further UB shifts")
>>> Oss-fuzz: 71138
>
> It's too late on this one, but it occurs to me that we probably want
>
> Link: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=71138
>
> rather than an abstract Oss-fuzz number. The bugtracker entry becomes
> public after 90d or when ClusterFuzz thinks we've fixed the bug, and the
> full link will be more useful to anyone interested.
I can try to remember doing so going forward. Let me adjust the one that's
still pending right away.
Jan
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