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arm64: mte: Avoid setting PG_mte_tagged if no tags cleared or restored

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[ Upstream commit a8e5e5146a ]

Prior to commit 69e3b846d8 ("arm64: mte: Sync tags for pages where PTE
is untagged"), mte_sync_tags() was only called for pte_tagged() entries
(those mapped with PROT_MTE). Therefore mte_sync_tags() could safely use
test_and_set_bit(PG_mte_tagged, &page->flags) without inadvertently
setting PG_mte_tagged on an untagged page.

The above commit was required as guests may enable MTE without any
control at the stage 2 mapping, nor a PROT_MTE mapping in the VMM.
However, the side-effect was that any page with a PTE that looked like
swap (or migration) was getting PG_mte_tagged set automatically. A
subsequent page copy (e.g. migration) copied the tags to the destination
page even if the tags were owned by KASAN.

This issue was masked by the page_kasan_tag_reset() call introduced in
commit e5b8d92189 ("arm64: mte: reset the page tag in page->flags").
When this commit was reverted (20794545c1), KASAN started reporting
access faults because the overriding tags in a page did not match the
original page->flags (with CONFIG_KASAN_HW_TAGS=y):

  BUG: KASAN: invalid-access in copy_page+0x10/0xd0 arch/arm64/lib/copy_page.S:26
  Read at addr f5ff000017f2e000 by task syz-executor.1/2218
  Pointer tag: [f5], memory tag: [f2]

Move the PG_mte_tagged bit setting from mte_sync_tags() to the actual
place where tags are cleared (mte_sync_page_tags()) or restored
(mte_restore_tags()).

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Reported-by: syzbot+c2c79c6d6eddc5262b77@syzkaller.appspotmail.com
Fixes: 69e3b846d8 ("arm64: mte: Sync tags for pages where PTE is untagged")
Cc: <stable@vger.kernel.org> # 5.14.x
Cc: Steven Price <steven.price@arm.com>
Cc: Andrey Konovalov <andreyknvl@gmail.com>
Cc: Vincenzo Frascino <vincenzo.frascino@arm.com>
Cc: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/0000000000004387dc05e5888ae5@google.com/
Reviewed-by: Steven Price <steven.price@arm.com>
Link: https://lore.kernel.org/r/20221006163354.3194102-1-catalin.marinas@arm.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Catalin Marinas 2022-10-06 17:33:54 +01:00 • committed by Justin Hammond
parent 831f24e715
commit 8186edef51
2 changed files with 13 additions and 3 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

9
arch/arm64/kernel/mte.c
View file

@ -53,7 +53,12 @@ static void mte_sync_page_tags(struct page *page, pte_t old_pte,
* the new page->flags are visible before the tags were updated.
*/
smp_wmb();
mte_clear_page_tags(page_address(page));
/*
* Test PG_mte_tagged again in case it was racing with another
* set_pte_at().
*/
if (!test_and_set_bit(PG_mte_tagged, &page->flags))
mte_clear_page_tags(page_address(page));
}
void mte_sync_tags(pte_t old_pte, pte_t pte)
@ -69,7 +74,7 @@ void mte_sync_tags(pte_t old_pte, pte_t pte)
/* if PG_mte_tagged is set, tags have already been initialised */
for (i = 0; i < nr_pages; i++, page++) {
if (!test_and_set_bit(PG_mte_tagged, &page->flags))
if (!test_bit(PG_mte_tagged, &page->flags))
mte_sync_page_tags(page, old_pte, check_swap,
pte_is_tagged);
}

7
arch/arm64/mm/mteswap.c
View file

@ -62,7 +62,12 @@ bool mte_restore_tags(swp_entry_t entry, struct page *page)
* the new page->flags are visible before the tags were updated.
*/
smp_wmb();
mte_restore_page_tags(page_address(page), tags);
/*
* Test PG_mte_tagged again in case it was racing with another
* set_pte_at().
*/
if (!test_and_set_bit(PG_mte_tagged, &page->flags))
mte_restore_page_tags(page_address(page), tags);
return true;
}