The patch titled
Subject: kasan: reset page tags properly with sampling
has been added to the -mm mm-unstable branch. Its filename is
kasan-reset-page-tags-properly-with-sampling.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/kasan-reset-page-tags-properly-with-sampling.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
Subject: kasan: reset page tags properly with sampling
Date: Tue, 24 Jan 2023 21:35:26 +0100
The implementation of page_alloc poisoning sampling assumed that
tag_clear_highpage resets page tags for __GFP_ZEROTAGS allocations.
However, this is no longer the case since commit 70c248aca9e7 ("mm: kasan:
Skip unpoisoning of user pages").
This leads to kernel crashes when MTE-enabled userspace mappings are used
with Hardware Tag-Based KASAN enabled.
Reset page tags for __GFP_ZEROTAGS allocations in post_alloc_hook().
Also clarify and fix related comments.
Link: https://lkml.kernel.org/r/24ea20c1b19c2b4b56cf9f5b354915f8dbccfc77.1674592496.git.andreyknvl@xxxxxxxxxx
Fixes: 44383cef54c0 ("kasan: allow sampling page_alloc allocations for HW_TAGS")
Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
Reported-by: Peter Collingbourne <pcc@xxxxxxxxxx>
Tested-by: Peter Collingbourne <pcc@xxxxxxxxxx>
Cc: Alexander Potapenko <glider@xxxxxxxxxx>
Cc: Andrey Ryabinin <ryabinin.a.a@xxxxxxxxx>
Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Cc: Marco Elver <elver@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/page_alloc.c | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)
--- a/mm/page_alloc.c~kasan-reset-page-tags-properly-with-sampling
+++ a/mm/page_alloc.c
@@ -2476,7 +2476,7 @@ inline void post_alloc_hook(struct page
bool init = !want_init_on_free() && want_init_on_alloc(gfp_flags) &&
!should_skip_init(gfp_flags);
bool zero_tags = init && (gfp_flags & __GFP_ZEROTAGS);
- bool reset_tags = !zero_tags;
+ bool reset_tags = true;
int i;
set_page_private(page, 0);
@@ -2503,7 +2503,7 @@ inline void post_alloc_hook(struct page
* (which happens only when memory should be initialized as well).
*/
if (zero_tags) {
- /* Initialize both memory and tags. */
+ /* Initialize both memory and memory tags. */
for (i = 0; i != 1 << order; ++i)
tag_clear_highpage(page + i);
@@ -2521,14 +2521,14 @@ inline void post_alloc_hook(struct page
} else {
/*
* KASAN decided to exclude this allocation from being
- * poisoned due to sampling. Skip poisoning as well.
+ * unpoisoned due to sampling. Skip poisoning as well.
*/
SetPageSkipKASanPoison(page);
}
}
/*
- * If memory tags have not been set, reset the page tags to ensure
- * page_address() dereferencing does not fault.
+ * If memory tags have not been set by KASAN, reset the page tags to
+ * ensure page_address() dereferencing does not fault.
*/
if (reset_tags) {
for (i = 0; i != 1 << order; ++i)
_
Patches currently in -mm which might be from andreyknvl@xxxxxxxxxx are
kasan-reset-page-tags-properly-with-sampling.patch
