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From: Ilya Leoshkevich <iii@linux.ibm.com>
To: Alexander Gordeev <agordeev@linux.ibm.com>,
        Alexander Potapenko <glider@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Christoph Lameter <cl@linux.com>, David Rientjes <rientjes@google.com>,
        Heiko Carstens <hca@linux.ibm.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>, Marco Elver <elver@google.com>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Pekka Enberg <penberg@kernel.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Vasily Gorbik <gor@linux.ibm.com>, Vlastimil Babka <vbabka@suse.cz>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Hyeonggon Yoo <42.hyeyoo@gmail.com>, kasan-dev@googlegroups.com,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        linux-s390@vger.kernel.org, linux-trace-kernel@vger.kernel.org,
        Mark Rutland <mark.rutland@arm.com>,
        Roman Gushchin <roman.gushchin@linux.dev>,
        Sven Schnelle <svens@linux.ibm.com>,
        Ilya Leoshkevich <iii@linux.ibm.com>
Subject: [PATCH v4 17/35] mm: kfence: Disable KMSAN when checking the canary
Date: Thu, 13 Jun 2024 17:34:19 +0200
Message-ID: <20240613153924.961511-18-iii@linux.ibm.com>
In-Reply-To: <20240613153924.961511-1-iii@linux.ibm.com>
References: <20240613153924.961511-1-iii@linux.ibm.com>
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KMSAN warns about check_canary() accessing the canary.

The reason is that, even though set_canary() is properly instrumented
and sets shadow, slub explicitly poisons the canary's address range
afterwards.

Unpoisoning the canary is not the right thing to do: only
check_canary() is supposed to ever touch it. Instead, disable KMSAN
checks around canary read accesses.

Reviewed-by: Alexander Potapenko <glider@google.com>
Tested-by: Alexander Potapenko <glider@google.com>
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
---
 mm/kfence/core.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/mm/kfence/core.c b/mm/kfence/core.c
index 964b8482275b..cce330d5b797 100644
--- a/mm/kfence/core.c
+++ b/mm/kfence/core.c
@@ -305,8 +305,14 @@ metadata_update_state(struct kfence_metadata *meta, enum kfence_object_state nex
 	WRITE_ONCE(meta->state, next);
 }
 
+#ifdef CONFIG_KMSAN
+#define CHECK_CANARY_ATTRIBUTES noinline __no_kmsan_checks
+#else
+#define CHECK_CANARY_ATTRIBUTES inline
+#endif
+
 /* Check canary byte at @addr. */
-static inline bool check_canary_byte(u8 *addr)
+static CHECK_CANARY_ATTRIBUTES bool check_canary_byte(u8 *addr)
 {
 	struct kfence_metadata *meta;
 	unsigned long flags;
@@ -341,7 +347,8 @@ static inline void set_canary(const struct kfence_metadata *meta)
 		*((u64 *)addr) = KFENCE_CANARY_PATTERN_U64;
 }
 
-static inline void check_canary(const struct kfence_metadata *meta)
+static CHECK_CANARY_ATTRIBUTES void
+check_canary(const struct kfence_metadata *meta)
 {
 	const unsigned long pageaddr = ALIGN_DOWN(meta->addr, PAGE_SIZE);
 	unsigned long addr = pageaddr;
-- 
2.45.1