Messages in this thread | | | Date | Fri, 18 Jun 2021 15:40:13 +0100 | From | Catalin Marinas <> | Subject | Re: [PATCH v16 1/7] arm64: mte: Handle race when synchronising tags |
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On Fri, Jun 18, 2021 at 02:28:20PM +0100, Steven Price wrote: > mte_sync_tags() used test_and_set_bit() to set the PG_mte_tagged flag > before restoring/zeroing the MTE tags. However if another thread were to > race and attempt to sync the tags on the same page before the first > thread had completed restoring/zeroing then it would see the flag is > already set and continue without waiting. This would potentially expose > the previous contents of the tags to user space, and cause any updates > that user space makes before the restoring/zeroing has completed to > potentially be lost. > > Since this code is run from atomic contexts we can't just lock the page > during the process. Instead implement a new (global) spinlock to protect > the mte_sync_page_tags() function. > > Fixes: 34bfeea4a9e9 ("arm64: mte: Clear the tags when a page is mapped in user-space with PROT_MTE") > Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> > Signed-off-by: Steven Price <steven.price@arm.com>
Although I reviewed this patch, I think we should drop it from this series and restart the discussion with the Chromium guys on what/if they need PROT_MTE with MAP_SHARED. It currently breaks if you have two PROT_MTE mappings but if they are ok with only one of the mappings being PROT_MTE, I'm happy to just document it.
Not sure whether subsequent patches depend on it though.
-- Catalin
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