linux-kernel - [PATCH v4 16/35] mm: slub: Unpoison the memchr

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20240613153924.961511-17-iii@linux.ibm.com>
Date: Thu, 13 Jun 2024 17:34:18 +0200
From: Ilya Leoshkevich <iii@...ux.ibm.com>
To: Alexander Gordeev <agordeev@...ux.ibm.com>,
        Alexander Potapenko <glider@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Christoph Lameter <cl@...ux.com>, David Rientjes <rientjes@...gle.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>, Marco Elver <elver@...gle.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Pekka Enberg <penberg@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Vasily Gorbik <gor@...ux.ibm.com>, Vlastimil Babka <vbabka@...e.cz>
Cc: Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Hyeonggon Yoo <42.hyeyoo@...il.com>, kasan-dev@...glegroups.com,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-s390@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
        Mark Rutland <mark.rutland@....com>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Sven Schnelle <svens@...ux.ibm.com>,
        Ilya Leoshkevich <iii@...ux.ibm.com>
Subject: [PATCH v4 16/35] mm: slub: Unpoison the memchr_inv() return value

Even though the KMSAN warnings generated by memchr_inv() are suppressed
by metadata_access_enable(), its return value may still be poisoned.

The reason is that the last iteration of memchr_inv() returns
`*start != value ? start : NULL`, where *start is poisoned. Because of
this, somewhat counterintuitively, the shadow value computed by
visitSelectInst() is equal to `(uintptr_t)start`.

The intention behind guarding memchr_inv() behind
metadata_access_enable() is to touch poisoned metadata without
triggering KMSAN, so unpoison its return value.

Acked-by: Vlastimil Babka <vbabka@...e.cz>
Signed-off-by: Ilya Leoshkevich <iii@...ux.ibm.com>
---
 mm/slub.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/mm/slub.c b/mm/slub.c
index a290f6c63e7b..b9101b2dc9aa 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1185,6 +1185,7 @@ static int check_bytes_and_report(struct kmem_cache *s, struct slab *slab,
 	metadata_access_enable();
 	fault = memchr_inv(kasan_reset_tag(start), value, bytes);
 	metadata_access_disable();
+	kmsan_unpoison_memory(&fault, sizeof(fault));
 	if (!fault)
 		return 1;
 
@@ -1291,6 +1292,7 @@ static void slab_pad_check(struct kmem_cache *s, struct slab *slab)
 	metadata_access_enable();
 	fault = memchr_inv(kasan_reset_tag(pad), POISON_INUSE, remainder);
 	metadata_access_disable();
+	kmsan_unpoison_memory(&fault, sizeof(fault));
 	if (!fault)
 		return;
 	while (end > fault && end[-1] == POISON_INUSE)
-- 
2.45.1