Re: [PATCH v2 0/4] support FEAT_MTE_STORE_ONLY feature

[Yeoreum Yun <yeoreum.yun@arm.com>]

Hi David.

> On 03.04.25 19:46, Yeoreum Yun wrote:
> > The FEAT_MTE_STORE_ONLY feature provides support for
> > tag check for store operation only. read operation is considered
> > as unchecked operation so it doesn't raise tag check fault.
>
> Can you add/share more details of what the implications are, how it would be
> used, who would set it, etc.
>
> Just from staring at this short paragraph leaves me rather clueless.
>

Sorry for my bad.

ARMv8.5 based processors introduce the Memory Tagging Extension (MTE) feature.
MTE is built on top of the ARMv8.0 virtual address tagging TBI
(Top Byte Ignore) feature and allows software to access a 4-bit
allocation tag for each 16-byte granule in the physical address space.
A logical tag is derived from bits 59-56 of the virtual
address used for the memory access. A CPU with MTE enabled will compare
the logical tag against the allocation tag and potentially raise an
tag check fault on mismatch, subject to system registers configuration.

Since ARMv8.9, FEAT_MTE_STORE_ONLY can be used to restrict raise of tag
check fault on store operation only.
For this, application can use PR_MTE_STORE_ONLY flag
when it sets the MTE setting with prctl().

This would be useful for debugging purpose
i.e) finding memory courruption point, use-after-free and etc.

--
Sincerely,
Yeoreum Yun