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Re: [PATCH 2/5] llc-coloring: improve checking while parsing
- To: Mykola Kvach <xakep.amatop@xxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Wed, 25 Mar 2026 07:14:38 +0100
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- Cc: "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Kamil Frankowicz <kamil.frankowicz@xxxxxxx>
- Delivery-date: Wed, 25 Mar 2026 06:14:43 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 24.03.2026 17:51, Mykola Kvach wrote:
> On Tue, Mar 24, 2026 at 6:37 PM Jan Beulich <jbeulich@xxxxxxxx> wrote:
>>
>> We can easily avoid the risk of wrapping UINT_MAX <-> 0 by applying a
>> check against the compile-time-constant maximum number of colors.
>>
>> Additionally the overflow checks suffered from an off-by-1, as the parsed
>> ranges are inclusive (e.g. end == start being possible, requiring 1 array
>> slot, while availability of 0 slots was checked in that case).
>>
>> Fixes: 6cdea3444eaf ("xen/arm: add Dom0 cache coloring support")
>> Reported-by: Kamil Frankowicz <kamil.frankowicz@xxxxxxx>
>
> For reference, I previously reported the UINT_MAX wraparound aspect here [1]
> and later also here [2].
I've added another Reported-by, yet I wonder (in particular wrt [2]): Why did
you not simply send patches? They likely would long have gone in.
Jan
> The off-by-1 in the inclusive-range accounting looks
> like a separate issue.
>
> Those threads also mention a few other related corner cases.
>
>
> Best regards,
> Mykola
>
>
> [1]
> https://patchew.org/Xen/20241217170637.233097-1-carlo.nonato@xxxxxxxxxxxxxxx/20241217170637.233097-5-carlo.nonato@xxxxxxxxxxxxxxx/#db5d6a67-61d9-48d3-b6c4-213c1cbbda21@xxxxxxxxx
> [2] https://lists.xen.org/archives/html/xen-devel/2026-01/msg00369.html
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