The patch titled
Subject: arm64: mte: reset the page tag in page->flags
has been added to the -mm tree. Its filename is
arm64-mte-reset-the-page-tag-in-page-flags.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/arm64-mte-reset-the-page-tag-in-page-flags.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/arm64-mte-reset-the-page-tag-in-page-flags.patch
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------------------------------------------------------
From: Vincenzo Frascino <vincenzo.frascino@xxxxxxx>
Subject: arm64: mte: reset the page tag in page->flags
The hardware tag-based KASAN for compatibility with the other modes stores
the tag associated to a page in page->flags. Due to this the kernel
faults on access when it allocates a page with an initial tag and the user
changes the tags.
Reset the tag associated by the kernel to a page in all the meaningful
places to prevent kernel faults on access.
Note: An alternative to this approach could be to modify page_to_virt().
This though could end up being racy, in fact if a CPU checks the
PG_mte_tagged bit and decides that the page is not tagged but another CPU
maps the same with PROT_MTE and becomes tagged the subsequent kernel
access would fail.
Link: https://lkml.kernel.org/r/9073d4e973747a6f78d5bdd7ebe17f290d087096.1606161801.git.andreyknvl@xxxxxxxxxx
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@xxxxxxx>
Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
Reviewed-by: Catalin Marinas <catalin.marinas@xxxxxxx>
Tested-by: Vincenzo Frascino <vincenzo.frascino@xxxxxxx>
Cc: Alexander Potapenko <glider@xxxxxxxxxx>
Cc: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
Cc: Branislav Rankov <Branislav.Rankov@xxxxxxx>
Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Cc: Evgenii Stepanov <eugenis@xxxxxxxxxx>
Cc: Kevin Brodsky <kevin.brodsky@xxxxxxx>
Cc: Marco Elver <elver@xxxxxxxxxx>
Cc: Vasily Gorbik <gor@xxxxxxxxxxxxx>
Cc: Will Deacon <will.deacon@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
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 insertions(+)
--- a/arch/arm64/kernel/hibernate.c~arm64-mte-reset-the-page-tag-in-page-flags
+++ a/arch/arm64/kernel/hibernate.c
@@ -371,6 +371,11 @@ 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);
--- a/arch/arm64/kernel/mte.c~arm64-mte-reset-the-page-tag-in-page-flags
+++ a/arch/arm64/kernel/mte.c
@@ -34,6 +34,15 @@ static void mte_sync_page_tags(struct pa
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));
}
--- a/arch/arm64/mm/copypage.c~arm64-mte-reset-the-page-tag-in-page-flags
+++ a/arch/arm64/mm/copypage.c
@@ -23,6 +23,15 @@ void copy_highpage(struct page *to, stru
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);
}
}
--- a/arch/arm64/mm/mteswap.c~arm64-mte-reset-the-page-tag-in-page-flags
+++ a/arch/arm64/mm/mteswap.c
@@ -53,6 +53,15 @@ bool mte_restore_tags(swp_entry_t entry,
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;
_
Patches currently in -mm which might be from vincenzo.frascino@xxxxxxx are
mm-vmalloc-fix-kasan-shadow-poisoning-size.patch
arm64-enable-armv85-a-asm-arch-option.patch
arm64-mte-add-in-kernel-mte-helpers.patch
arm64-mte-reset-the-page-tag-in-page-flags.patch
arm64-mte-add-in-kernel-tag-fault-handler.patch
arm64-kasan-allow-enabling-in-kernel-mte.patch
arm64-mte-convert-gcr_user-into-an-exclude-mask.patch
arm64-mte-switch-gcr_el1-in-kernel-entry-and-exit.patch
kasan-mm-untag-page-address-in-free_reserved_area.patch
kselftest-arm64-check-gcr_el1-after-context-switch.patch
