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From: Michal Hocko <mhocko@kernel.org>
To: Waiman Long <longman@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	David Howells <dhowells@redhat.com>,
	Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>,
	James Morris <jmorris@namei.org>,
	"Serge E. Hallyn" <serge@hallyn.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Joe Perches <joe@perches.com>,
	Matthew Wilcox <willy@infradead.org>,
	David Rientjes <rientjes@google.com>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Dan Carpenter <dan.carpenter@oracle.com>,
	David Sterba <dsterba@suse.cz>,
	"Jason A . Donenfeld" <Jason@zx2c4.com>,
	linux-mm@kvack.org, keyrings@vger.kernel.org,
	linux-kernel@vger.kernel.org, linux-crypto@vger.kernel.org,
	linux-pm@vger.kernel.org,
	linux-stm32@st-md-mailman.stormreply.com,
	linux-amlogic@lists.infradead.org,
	linux-mediatek@lists.infradead.org,
	linuxppc-dev@lists.ozlabs.org,
	virtualization@lists.linux-foundation.org,
	netdev@vger.kernel.org, linux-ppp@vger.kernel.org,
	wireguard@lists.zx2c4.com, linux-wireless@vger.kernel.org,
	devel@driverdev.osuosl.org, linux-scsi@vger.kernel.org,
	target-devel@vger.kernel.org, linux-btrfs@vger.kernel.org,
	linux-cifs@vger.kernel.org, linux-fscrypt@vger.kernel.org,
	ecryptfs@vger.kernel.org, kasan-dev@googlegroups.com,
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	linux-sctp@vger.kernel.org, linux-nfs@vger.kernel.org,
	tipc-discussion@lists.sourceforge.net,
	linux-security-module@vger.kernel.org,
	linux-integrity@vger.kernel.org, stable@vger.kernel.org
Subject: Re: [PATCH v4 1/3] mm/slab: Use memzero_explicit() in kzfree()
Date: Tue, 16 Jun 2020 08:42:08 +0200
Message-ID: <20200616064208.GA9499@dhcp22.suse.cz> (raw)
In-Reply-To: <20200616015718.7812-2-longman@redhat.com>

On Mon 15-06-20 21:57:16, Waiman Long wrote:
> The kzfree() function is normally used to clear some sensitive
> information, like encryption keys, in the buffer before freeing it back
> to the pool. Memset() is currently used for the buffer clearing. However,
> it is entirely possible that the compiler may choose to optimize away the
> memory clearing especially if LTO is being used. To make sure that this
> optimization will not happen, memzero_explicit(), which is introduced
> in v3.18, is now used in kzfree() to do the clearing.
> 
> Fixes: 3ef0e5ba4673 ("slab: introduce kzfree()")
> Cc: stable@vger.kernel.org
> Signed-off-by: Waiman Long <longman@redhat.com>

Acked-by: Michal Hocko <mhocko@suse.com>

Although I am not really sure this is a stable material. Is there any
known instance where the memset was optimized out from kzfree?

> ---
>  mm/slab_common.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/slab_common.c b/mm/slab_common.c
> index 9e72ba224175..37d48a56431d 100644
> --- a/mm/slab_common.c
> +++ b/mm/slab_common.c
> @@ -1726,7 +1726,7 @@ void kzfree(const void *p)
>  	if (unlikely(ZERO_OR_NULL_PTR(mem)))
>  		return;
>  	ks = ksize(mem);
> -	memset(mem, 0, ks);
> +	memzero_explicit(mem, ks);
>  	kfree(mem);
>  }
>  EXPORT_SYMBOL(kzfree);
> -- 
> 2.18.1
> 

-- 
Michal Hocko
SUSE Labs

  parent reply index

Thread overview: 28+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-16  1:57 [PATCH v4 0/3] mm, treewide: Rename kzfree() to kfree_sensitive() Waiman Long
2020-06-16  1:57 ` [PATCH v4 1/3] mm/slab: Use memzero_explicit() in kzfree() Waiman Long
2020-06-16  3:30   ` Eric Biggers
2020-06-16 13:05     ` Waiman Long
2020-06-16 15:46     ` David Howells
2020-06-16  6:42   ` Michal Hocko [this message]
2020-06-16  9:08     ` Dan Carpenter
2020-06-16  1:57 ` [PATCH v4 2/3] mm, treewide: Rename kzfree() to kfree_sensitive() Waiman Long
2020-06-16 14:26   ` Dan Carpenter
2020-06-16 15:05     ` Waiman Long
2020-06-16  1:57 ` [PATCH v4 3/3] btrfs: Use kfree() in btrfs_ioctl_get_subvol_info() Waiman Long
2020-06-16 14:48   ` David Sterba
2020-06-16 15:05     ` Waiman Long
2020-06-16 18:53 ` [PATCH v4 0/3] mm, treewide: Rename kzfree() to kfree_sensitive() Joe Perches
2020-06-16 19:43   ` Waiman Long
2020-06-16 19:46   ` Jason A. Donenfeld
2020-06-16 20:01   ` Waiman Long
2020-06-16 21:14   ` Matthew Wilcox
2020-06-16 23:01   ` David Sterba
2020-06-17  0:37     ` Matthew Wilcox
2020-06-17  7:12       ` Michal Hocko
2020-06-17 11:08         ` Matthew Wilcox
2020-06-17 11:31           ` Michal Hocko
2020-06-17 12:23             ` Matthew Wilcox
2020-06-17 12:55               ` Michal Hocko
2020-06-17  8:03       ` Jo -l
2020-06-17 21:31   ` Denis Efremov
2020-06-17 23:12     ` Joe Perches

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