[PATCH] arm64: mte: Do not set PG_mte_tagged if tags were not initialized

[Will Deacon]

On Thu, 20 Apr 2023 14:43:27 -0700, Peter Collingbourne wrote:
> The mte_sync_page_tags() function sets PG_mte_tagged if it initializes
> page tags. Then we return to mte_sync_tags(), which sets PG_mte_tagged
> again. At best, this is redundant. However, it is possible for
> mte_sync_page_tags() to return without having initialized tags for the
> page, i.e. in the case where check_swap is true (non-compound page),
> is_swap_pte(old_pte) is false and pte_is_tagged is false. So at worst,
> we set PG_mte_tagged on a page with uninitialized tags. This can happen
> if, for example, page migration causes a PTE for an untagged page to
> be replaced. If the userspace program subsequently uses mprotect() to
> enable PROT_MTE for that page, the uninitialized tags will be exposed
> to userspace.
> 
> [...]

Applied to arm64 (for-next/fixes), thanks!

[1/1] arm64: mte: Do not set PG_mte_tagged if tags were not initialized
      https://git.kernel.org/arm64/c/c4c597f1b367

Cheers,
-- 
Will

https://fixes.arm64.dev
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