Re: [PATCH v4 1/3] mm/slab: Use memzero_explicit() in kzfree()
From: Michal Hocko <mhocko@kernel.org>
Date: 2020-06-16 06:42:22
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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?
quoted hunk ↗ jump to hunk
--- 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