[PATCH 5.18 0139/1095] arm64: kasan: Revert "arm64: mte: reset the page tag in page->flags"

Greg Kroah-Hartman
2022-08-15T20:27:23Z

From: Catalin Marinas <catalin.marinas@arm.com>

[ Upstream commit 20794545c14692094a882d2221c251c4573e6adf ]

This reverts commit e5b8d9218951e59df986f627ec93569a0d22149b.

Pages mapped in user-space with PROT_MTE have the allocation tags either
zeroed or copied/restored to some user values. In order for the kernel
to access such pages via page_address(), resetting the tag in
page->flags was necessary. This tag resetting was deferred to
set_pte_at() -> mte_sync_page_tags() but it can race with another CPU
reading the flags (via page_to_virt()):

P0 (mte_sync_page_tags): P1 (memcpy from virt_to_page):
Rflags!=0xff
Wflags=0xff
DMB (doesn't help)
Wtags=0
Rtags=0 // fault

Since now the post_alloc_hook() function resets the page->flags tag when
unpoisoning is skipped for user pages (including the __GFP_ZEROTAGS
case), revert the arm64 commit calling page_kasan_tag_reset().

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Vincenzo Frascino <vincenzo.frascino@arm.com>
Cc: Andrey Konovalov <andreyknvl@gmail.com>
Cc: Peter Collingbourne <pcc@google.com>
Reviewed-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Acked-by: Andrey Konovalov <andreyknvl@gmail.com>
Link: https://lore.kernel.org/r/20220610152141.2148929-5-catalin.marinas@arm.com
Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/arm64/kernel/hibernate.c | 5 -----
arch/arm64/kernel/mte.c | 9 ---------
arch/arm64/mm/copypage.c | 9 ---------
arch/arm64/mm/mteswap.c | 9 ---------
4 files changed, 32 deletions(-)

diff --git a/arch/arm64/kernel/hibernate.c b/arch/arm64/kernel/hibernate.c
index 6328308be272..7754ef328657 100644
--- a/arch/arm64/kernel/hibernate.c
+++ b/arch/arm64/kernel/hibernate.c
@@ -300,11 +300,6 @@ static void swsusp_mte_restore_tags(void)
unsigned long pfn = xa_state.xa_index;
struct page *page = pfn_to_online_page(pfn);

- /*
- * It is not required to invoke page_kasan_tag_reset(page)
- * at this point since the tags stored in page->flags are
- * already restored.
- */
mte_restore_page_tags(page_address(page), tags);

mte_free_tag_storage(tags);
diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c
index d502703e8373..d565ae25e48f 100644
--- a/arch/arm64/kernel/mte.c
+++ b/arch/arm64/kernel/mte.c
@@ -47,15 +47,6 @@ static void mte_sync_page_tags(struct page *page, pte_t old_pte,
if (!pte_is_tagged)
return;

- page_kasan_tag_reset(page);
- /*
- * We need smp_wmb() in between setting the flags and clearing the
- * tags because if another thread reads page->flags and builds a
- * tagged address out of it, there is an actual dependency to the
- * memory access, but on the current thread we do not guarantee that
- * the new page->flags are visible before the tags were updated.
- */
- smp_wmb();
mte_clear_page_tags(page_address(page));
}

diff --git a/arch/arm64/mm/copypage.c b/arch/arm64/mm/copypage.c
index 0dea80bf6de4..24913271e898 100644
--- a/arch/arm64/mm/copypage.c
+++ b/arch/arm64/mm/copypage.c
@@ -23,15 +23,6 @@ void copy_highpage(struct page *to, struct page *from)

if (system_supports_mte() && test_bit(PG_mte_tagged, &from->flags)) {
set_bit(PG_mte_tagged, &to->flags);
- page_kasan_tag_reset(to);
- /*
- * We need smp_wmb() in between setting the flags and clearing the
- * tags because if another thread reads page->flags and builds a
- * tagged address out of it, there is an actual dependency to the
- * memory access, but on the current thread we do not guarantee that
- * the new page->flags are visible before the tags were updated.
- */
- smp_wmb();
mte_copy_page_tags(kto, kfrom);
}
}
diff --git a/arch/arm64/mm/mteswap.c b/arch/arm64/mm/mteswap.c
index a9e50e930484..4334dec93bd4 100644
--- a/arch/arm64/mm/mteswap.c
+++ b/arch/arm64/mm/mteswap.c
@@ -53,15 +53,6 @@ bool mte_restore_tags(swp_entry_t entry, struct page *page)
if (!tags)
return false;

- page_kasan_tag_reset(page);
- /*
- * We need smp_wmb() in between setting the flags and clearing the
- * tags because if another thread reads page->flags and builds a
- * tagged address out of it, there is an actual dependency to the
- * memory access, but on the current thread we do not guarantee that
- * the new page->flags are visible before the tags were updated.
- */
- smp_wmb();
mte_restore_page_tags(page_address(page), tags);

return true;
--
2.35.1