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Re: [XEN PATCH v2] xen/flask: limit sidtable size
- To: Sergiy Kibrik <sergiy_kibrik@xxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Fri, 26 Sep 2025 08:41:11 +0200
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Julien Grall <julien@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx, "Daniel P. Smith" <dpsmith@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Fri, 26 Sep 2025 06:41:19 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 26.09.2025 08:32, Sergiy Kibrik wrote:
> 06.09.25 01:01, Daniel P. Smith:
>> On 9/2/25 05:41, Jan Beulich wrote:
>>> On 01.09.2025 12:52, Sergiy Kibrik wrote:
>>>> --- a/xen/common/Kconfig
>>>> +++ b/xen/common/Kconfig
>>>> @@ -418,6 +418,17 @@ config XSM_FLASK_AVC_STATS
>>>>
>>>> If unsure, say Y.
>>>>
>>>> +config XSM_FLASK_SIDTABLE_ORDER
>>>> + int "Maximum number of security identifiers (base-2 exponent)" if EXPERT
>>>> + range 4 32
>>>> + default 32
>>> When 32 is chosen (i.e. also the default when the prompt is hidden), ...
>>>
>>>> --- a/xen/xsm/flask/ss/sidtab.c
>>>> +++ b/xen/xsm/flask/ss/sidtab.c
>>>> @@ -14,6 +14,8 @@
>>>> #include "security.h"
>>>> #include "sidtab.h"
>>>>
>>>> +#define SID_LIMIT ((1UL << CONFIG_XSM_FLASK_SIDTABLE_ORDER) - 1)
>>> ... for Arm32 I expect either already the compiler will not like this
>>> construct,
>>> or the latest an UBSAN checker would object.
>
> you're right, arm32 toolchain is not building this.
> Would the following be acceptable then? :
>
> #define SID_LIMIT ((1ULL << CONFIG_XSM_FLASK_SIDTABLE_ORDER) - 1)
Personally I'd consider this an abuse of the ULL suffix. But it'll be Daniel
to judge in the end.
Jan
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