From: Vlastimil Babka <vbabka@suse.cz>
To: Stephen Boyd <swboyd@chromium.org>,
Andrew Morton <akpm@linux-foundation.org>
Cc: linux-kernel@vger.kernel.org, Christoph Lameter <cl@linux.com>,
Pekka Enberg <penberg@kernel.org>,
David Rientjes <rientjes@google.com>,
Joonsoo Kim <iamjoonsoo.kim@lge.com>,
linux-mm@kvack.org, Petr Mladek <pmladek@suse.com>,
Joe Perches <joe@perches.com>
Subject: Re: [PATCH v3 4/4] slub: Force on no_hash_pointers when slub_debug is enabled
Date: Wed, 2 Jun 2021 12:50:03 +0200 [thread overview]
Message-ID: <5b1e2626-1d70-26cd-bb17-f7f8f80ac377@suse.cz> (raw)
In-Reply-To: <20210601182202.3011020-5-swboyd@chromium.org>
On 6/1/21 8:22 PM, Stephen Boyd wrote:
> 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 <swboyd@chromium.org>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
> ---
> 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);
>
> +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 fwnode_handle *fwnode,
> bool no_hash_pointers __ro_after_init;
> EXPORT_SYMBOL_GPL(no_hash_pointers);
>
> -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 = 0;
>
> + /* Print slub debugging pointers without hashing */
> + if (static_branch_unlikely(&slub_debug_enabled))
> + no_hash_pointers_enable(NULL);
> +
> kmem_cache_node = &boot_kmem_cache_node;
> kmem_cache = &boot_kmem_cache;
>
>
next prev parent reply other threads:[~2021-06-02 15:18 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-01 18:21 [PATCH v3 0/4] slub: Print non-hashed pointers in slub debugging Stephen Boyd
2021-06-01 18:21 ` [PATCH v3 1/4] slub: Restore slub_debug=- behavior Stephen Boyd
2021-06-01 18:22 ` [PATCH v3 2/4] slub: Actually use 'message' in restore_bytes() Stephen Boyd
2021-06-01 18:22 ` [PATCH v3 3/4] slub: Indicate slab_fix() uses printf formats Stephen Boyd
2021-06-06 0:06 ` David Rientjes
2021-06-01 18:22 ` [PATCH v3 4/4] slub: Force on no_hash_pointers when slub_debug is enabled Stephen Boyd
2021-06-01 22:45 ` kernel test robot
2021-06-02 0:26 ` Andrew Morton
2021-06-02 1:03 ` Stephen Boyd
2021-06-02 10:48 ` Vlastimil Babka
2021-06-02 10:50 ` Vlastimil Babka [this message]
2021-06-03 13:15 ` Petr Mladek
2021-09-20 14:29 ` Kees Cook
2021-09-20 18:23 ` Stephen Boyd
2021-09-20 18:28 ` Kees Cook
2021-09-20 18:44 ` Stephen Boyd
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