FROMLIST: kasan: reset page tags properly with sampling
[The patch is in the mm-unstable tree.]
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.
Fixes: 44383cef54c0 ("kasan: allow sampling page_alloc allocations for HW_TAGS")
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Reported-by: Peter Collingbourne <pcc@google.com>
Tested-by: Peter Collingbourne <pcc@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Marco Elver <elver@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Bug: 238286329
Bug: 264310057
Link: https://lore.kernel.org/all/5dbd866714b4839069e2d8469ac45b60953db290.1674592780.git.andreyknvl@google.com/
Change-Id: Iea4234bcf7e35337c8063827b07039583bca9c66
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 0876589..5f5a9528 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2497,7 +2497,7 @@
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);
@@ -2524,7 +2524,7 @@
* (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);
@@ -2542,14 +2542,15 @@
} else {
/*
* KASAN decided to exclude this allocation from being
- * poisoned due to sampling. Skip poisoning as well.
+ * (un)poisoned due to sampling. Make KASAN skip
+ * poisoning when the allocation is freed.
*/
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)
