linux-kernel - Re: [PATCH 5.10 518/530] mm, slub: enable slub_debug static key when creating cache with explicit debug flags

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: <dd590c4d-cb37-fd38-3ad7-96f677403b3c@suse.cz>
Date:   Wed, 12 May 2021 17:35:28 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org
Cc:     stable@...r.kernel.org, Oliver Glitta <glittao@...il.com>,
        David Rientjes <rientjes@...gle.com>,
        Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Sasha Levin <sashal@...nel.org>
Subject: Re: [PATCH 5.10 518/530] mm, slub: enable slub_debug static key when
 creating cache with explicit debug flags

On 5/12/21 4:50 PM, Greg Kroah-Hartman wrote:
> From: Vlastimil Babka <vbabka@...e.cz>
> 
> [ Upstream commit 1f0723a4c0df36cbdffc6fac82cd3c5d57e06d66 ]
> 
> Commit ca0cab65ea2b ("mm, slub: introduce static key for slub_debug()")
> introduced a static key to optimize the case where no debugging is
> enabled for any cache.  The static key is enabled when slub_debug boot
> parameter is passed, or CONFIG_SLUB_DEBUG_ON enabled.
> 
> However, some caches might be created with one or more debugging flags
> explicitly passed to kmem_cache_create(), and the commit missed this.
> Thus the debugging functionality would not be actually performed for
> these caches unless the static key gets enabled by boot param or config.
> 
> This patch fixes it by checking for debugging flags passed to
> kmem_cache_create() and enabling the static key accordingly.
> 
> Note such explicit debugging flags should not be used outside of
> debugging and testing as they will now enable the static key globally.
> btrfs_init_cachep() creates a cache with SLAB_RED_ZONE but that's a
> mistake that's being corrected [1].  rcu_torture_stats() creates a cache
> with SLAB_STORE_USER, but that is a testing module so it's OK and will
> start working as intended after this patch.
> 
> Also note that in case of backports to kernels before v5.12 that don't
> have 59450bbc12be ("mm, slab, slub: stop taking cpu hotplug lock"),
> static_branch_enable_cpuslocked() should be used.
> 
> [1] https://lore.kernel.org/linux-btrfs/20210315141824.26099-1-dsterba@suse.com/
> 
> Link: https://lkml.kernel.org/r/20210315153415.24404-1-vbabka@suse.cz
> Fixes: ca0cab65ea2b ("mm, slub: introduce static key for slub_debug()")
> Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
> Reported-by: Oliver Glitta <glittao@...il.com>
> Acked-by: David Rientjes <rientjes@...gle.com>
> Cc: Christoph Lameter <cl@...ux.com>
> Cc: Pekka Enberg <penberg@...nel.org>
> Cc: Joonsoo Kim <iamjoonsoo.kim@....com>
> Cc: "Paul E. McKenney" <paulmck@...nel.org>
> Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
> Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
> Signed-off-by: Sasha Levin <sashal@...nel.org>

Uh, rather not release this to stable without the followup fix:
https://lore.kernel.org/linux-mm/20210504120019.26791-1-vbabka@suse.cz/

> ---
>  mm/slub.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/mm/slub.c b/mm/slub.c
> index 05a501b67cd5..e4f7978d43c2 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -3779,6 +3779,15 @@ static int calculate_sizes(struct kmem_cache *s, int forced_order)
>  
>  static int kmem_cache_open(struct kmem_cache *s, slab_flags_t flags)
>  {
> +#ifdef CONFIG_SLUB_DEBUG
> +	/*
> +	 * If no slub_debug was enabled globally, the static key is not yet
> +	 * enabled by setup_slub_debug(). Enable it if the cache is being
> +	 * created with any of the debugging flags passed explicitly.
> +	 */
> +	if (flags & SLAB_DEBUG_FLAGS)
> +		static_branch_enable(&slub_debug_enabled);
> +#endif
>  	s->flags = kmem_cache_flags(s->size, flags, s->name);
>  #ifdef CONFIG_SLAB_FREELIST_HARDENED
>  	s->random = get_random_long();
>