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Tue, 01 Jun 2021 11:22:10 -0700 (PDT) Received: from smtp.gmail.com ([2620:15c:202:201:ee82:b2a7:c8bd:18e7]) by smtp.gmail.com with ESMTPSA id g29sm14510982pgm.11.2021.06.01.11.22.09 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 01 Jun 2021 11:22:09 -0700 (PDT) From: Stephen Boyd To: Andrew Morton Cc: linux-kernel@vger.kernel.org, Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Vlastimil Babka , linux-mm@kvack.org, Petr Mladek , Joe Perches Subject: [PATCH v3 4/4] slub: Force on no_hash_pointers when slub_debug is enabled Date: Tue, 1 Jun 2021 11:22:02 -0700 Message-Id: <20210601182202.3011020-5-swboyd@chromium.org> X-Mailer: git-send-email 2.32.0.rc0.204.g9fa02ecfa5-goog In-Reply-To: <20210601182202.3011020-1-swboyd@chromium.org> References: <20210601182202.3011020-1-swboyd@chromium.org> MIME-Version: 1.0 X-Rspamd-Queue-Id: 2754AA000262 Authentication-Results: imf23.hostedemail.com; dkim=pass header.d=chromium.org header.s=google header.b=JdKbC5Wa; spf=pass (imf23.hostedemail.com: domain of swboyd@chromium.org designates 209.85.210.175 as permitted sender) smtp.mailfrom=swboyd@chromium.org; dmarc=pass (policy=none) header.from=chromium.org X-Rspamd-Server: rspam04 X-Stat-Signature: 86ho41mcebhkgo1m649gzh576eidtt8x X-HE-Tag: 1622571720-535438 Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Obscuring the pointers that slub shows when debugging makes for some confusing slub debug messages: Padding overwritten. 0x0000000079f0674a-0x000000000d4dce17 Those addresses are hashed for kernel security reasons. If we're trying to be secure with slub_debug on the commandline we have some big problems given that we dump whole chunks of kernel memory to the kernel logs. Let's force on the no_hash_pointers commandline flag when slub_debug is on the commandline. This makes slub debug messages more meaningful and if by chance a kernel address is in some slub debug object dump we will have a better chance of figuring out what went wrong. Note that we don't use %px in the slub code because we want to reduce the number of places that %px is used in the kernel. This also nicely prints a big fat warning at kernel boot if slub_debug is on the commandline so that we know that this kernel shouldn't be used on production systems. Signed-off-by: Stephen Boyd --- include/linux/kernel.h | 2 ++ lib/vsprintf.c | 2 +- mm/slub.c | 4 ++++ 3 files changed, 7 insertions(+), 1 deletion(-) diff --git a/include/linux/kernel.h b/include/linux/kernel.h index 15d8bad3d2f2..bf950621febf 100644 --- a/include/linux/kernel.h +++ b/include/linux/kernel.h @@ -357,6 +357,8 @@ int sscanf(const char *, const char *, ...); extern __scanf(2, 0) int vsscanf(const char *, const char *, va_list); =20 +extern int no_hash_pointers_enable(char *str); + extern int get_option(char **str, int *pint); extern char *get_options(const char *str, int nints, int *ints); extern unsigned long long memparse(const char *ptr, char **retptr); diff --git a/lib/vsprintf.c b/lib/vsprintf.c index f0c35d9b65bf..cc281f5895f9 100644 --- a/lib/vsprintf.c +++ b/lib/vsprintf.c @@ -2186,7 +2186,7 @@ char *fwnode_string(char *buf, char *end, struct fw= node_handle *fwnode, bool no_hash_pointers __ro_after_init; EXPORT_SYMBOL_GPL(no_hash_pointers); =20 -static int __init no_hash_pointers_enable(char *str) +int __init no_hash_pointers_enable(char *str) { if (no_hash_pointers) return 0; diff --git a/mm/slub.c b/mm/slub.c index bf4949115412..a722794f1dbd 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -4460,6 +4460,10 @@ void __init kmem_cache_init(void) if (debug_guardpage_minorder()) slub_max_order =3D 0; =20 + /* Print slub debugging pointers without hashing */ + if (static_branch_unlikely(&slub_debug_enabled)) + no_hash_pointers_enable(NULL); + kmem_cache_node =3D &boot_kmem_cache_node; kmem_cache =3D &boot_kmem_cache; =20 --=20 https://chromeos.dev