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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4aa7f3229dbsm15896115e9.1.2026.10.28.13.56.34 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 28 Oct 2026 13:56:34 -0700 (PDT) Date: Wed, 28 Oct 2026 20:56:33 +0000 From: David Laight To: Eric Biggers Cc: Mohamad Raizudeen , ardb@kernel.org, Jason@zx2c4.com, linux-crypto@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] lib/crypto: aes: use memzero_explicit() instead of memset() Message-ID: <20261028205633.7625d789@pumpkin> In-Reply-To: <20261028155134.GA4041913@google.com> References: <20261028142636.5888-1-raizudeen.kerneldev@gmail.com> <20261028155134.GA4041913@google.com> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Wed, 28 Oct 2026 15:51:34 +0000 Eric Biggers wrote: > On Wed, Oct 28, 2026 at 07:56:36PM +0530, Mohamad Raizudeen wrote: > > aes_gcm_decrypt() and aes_ccm_decrypt() use plain memset() to wipe the > > output buffer when authentication fails. But the compiler can optimize > > that wipe away, so use memzero_explicit() instead of memset(). > > > > This matches every other sensitive wipes in this file, which already > > uses memzero_explicit() for keystream blocks, tmp buffers, ctx > > teardowns. > > > > Signed-off-by: Mohamad Raizudeen > > --- > > lib/crypto/aes.c | 4 ++-- > > 1 file changed, 2 insertions(+), 2 deletions(-) > > > > diff --git a/lib/crypto/aes.c b/lib/crypto/aes.c > > index e1c191551736..7814ef525239 100644 > > --- a/lib/crypto/aes.c > > +++ b/lib/crypto/aes.c > > @@ -1733,7 +1733,7 @@ int aes_gcm_decrypt(u8 *dst, const u8 *src, size_t data_len, const u8 *authtag, > > * Clear the inauthentic decrypted data so that callers won't > > * receive it even if they fail to correctly handle errors. > > */ > > - memset(dst, 0, data_len); > > + memzero_explicit(dst, data_len); > > This isn't for "zeroization" (making the data unavailable in ramdumps), > though. It's just so the caller doesn't accidentally use the > inauthentic data, as the comment right above it states. It is also a parameter so has to be zeroed anyway. memzero_explicit() is used to clear on-stack buffers. David > > - Eric >