This reverts commit e5b8d9218951e59df986f627ec93569a0d22149b.
On a system with MTE and KASAN_HW_TAGS enabled, when a page is allocated
kasan_unpoison_pages() sets a random tag and saves it in page->flags.
page_to_virt() re-creates the correct tagged pointer.
If such page is mapped in user-space with PROT_MTE, the architecture
code will set the tag to 0 and a subsequent page_to_virt() dereference
will fault. The reverted commit aimed to fix this by resetting the tag
in page->flags so that it is 0xff (match-all, not faulting). However,
setting the tags and flags can race with another CPU reading the flags
(page_to_virt()) and barriers can't help:
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 clearing the flags in the arch code doesn't help, revert the patch
altogether. In addition, remove the page_kasan_tag_reset() call in
tag_clear_highpage() since the core kasan code should take care of
resetting the page tag.
Signed-off-by: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Will Deacon <will@xxxxxxxxxx>
Cc: Vincenzo Frascino <vincenzo.frascino@xxxxxxx>
Cc: Andrey Konovalov <andreyknvl@xxxxxxxxx>
Cc: Peter Collingbourne <pcc@xxxxxxxxxx>
---
arch/arm64/kernel/hibernate.c | 5 -----
arch/arm64/kernel/mte.c | 9 ---------
arch/arm64/mm/copypage.c | 9 ---------
arch/arm64/mm/fault.c | 1 -
arch/arm64/mm/mteswap.c | 9 ---------
5 files changed, 33 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 78b3e0f8e997..90994aca54f3 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 b5447e53cd73..70a71f38b6a9 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/fault.c b/arch/arm64/mm/fault.c
index 77341b160aca..f2f21cd6d43f 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -926,6 +926,5 @@ 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));
- page_kasan_tag_reset(page);
set_bit(PG_mte_tagged, &page->flags);
}
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;
