diff options
| author | Catalin Marinas <catalin.marinas@arm.com> | 2022-11-03 18:10:35 -0700 |
|---|---|---|
| committer | Marc Zyngier <maz@kernel.org> | 2022-11-29 09:26:07 +0000 |
| commit | e059853d14ca4ed0f6a190d7109487918a22a976 (patch) | |
| tree | 8aa2c02019059c64820dafc2a9eedcdd524d6f58 /arch/arm64/mm | |
| parent | b0284cd29a957e62d60c2886fd663be93c56f9c0 (diff) | |
arm64: mte: Fix/clarify the PG_mte_tagged semantics
Currently the PG_mte_tagged page flag mostly means the page contains
valid tags and it should be set after the tags have been cleared or
restored. However, in mte_sync_tags() it is set before setting the tags
to avoid, in theory, a race with concurrent mprotect(PROT_MTE) for
shared pages. However, a concurrent mprotect(PROT_MTE) with a copy on
write in another thread can cause the new page to have stale tags.
Similarly, tag reading via ptrace() can read stale tags if the
PG_mte_tagged flag is set before actually clearing/restoring the tags.
Fix the PG_mte_tagged semantics so that it is only set after the tags
have been cleared or restored. This is safe for swap restoring into a
MAP_SHARED or CoW page since the core code takes the page lock. Add two
functions to test and set the PG_mte_tagged flag with acquire and
release semantics. The downside is that concurrent mprotect(PROT_MTE) on
a MAP_SHARED page may cause tag loss. This is already the case for KVM
guests if a VMM changes the page protection while the guest triggers a
user_mem_abort().
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
[pcc@google.com: fix build with CONFIG_ARM64_MTE disabled]
Signed-off-by: Peter Collingbourne <pcc@google.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Reviewed-by: Steven Price <steven.price@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Peter Collingbourne <pcc@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20221104011041.290951-3-pcc@google.com
Diffstat (limited to 'arch/arm64/mm')
| -rw-r--r-- | arch/arm64/mm/copypage.c | 5 | ||||
| -rw-r--r-- | arch/arm64/mm/fault.c | 2 | ||||
| -rw-r--r-- | arch/arm64/mm/mteswap.c | 2 |
3 files changed, 5 insertions, 4 deletions
diff --git a/arch/arm64/mm/copypage.c b/arch/arm64/mm/copypage.c index 24913271e898..731d8a35701e 100644 --- a/arch/arm64/mm/copypage.c +++ b/arch/arm64/mm/copypage.c @@ -21,9 +21,10 @@ void copy_highpage(struct page *to, struct page *from) copy_page(kto, kfrom); - if (system_supports_mte() && test_bit(PG_mte_tagged, &from->flags)) { - set_bit(PG_mte_tagged, &to->flags); + if (system_supports_mte() && page_mte_tagged(from)) { + page_kasan_tag_reset(to); mte_copy_page_tags(kto, kfrom); + set_page_mte_tagged(to); } } EXPORT_SYMBOL(copy_highpage); diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c index 5b391490e045..629e886ceec4 100644 --- a/arch/arm64/mm/fault.c +++ b/arch/arm64/mm/fault.c @@ -934,5 +934,5 @@ struct page *alloc_zeroed_user_highpage_movable(struct vm_area_struct *vma, void tag_clear_highpage(struct page *page) { mte_zero_clear_page_tags(page_address(page)); - set_bit(PG_mte_tagged, &page->flags); + set_page_mte_tagged(page); } diff --git a/arch/arm64/mm/mteswap.c b/arch/arm64/mm/mteswap.c index bed803d8e158..70f913205db9 100644 --- a/arch/arm64/mm/mteswap.c +++ b/arch/arm64/mm/mteswap.c @@ -24,7 +24,7 @@ int mte_save_tags(struct page *page) { void *tag_storage, *ret; - if (!test_bit(PG_mte_tagged, &page->flags)) + if (!page_mte_tagged(page)) return 0; tag_storage = mte_allocate_tag_storage(); |