linux-kernel - [PATCH 5.10 571/717] crypto: ecdh - avoid unaligned accesses in ecdh_set

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Date:   Mon, 28 Dec 2020 13:49:29 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Ard Biesheuvel <ardb@...nel.org>,
        Herbert Xu <herbert@...dor.apana.org.au>
Subject: [PATCH 5.10 571/717] crypto: ecdh - avoid unaligned accesses in ecdh_set_secret()

From: Ard Biesheuvel <ardb@...nel.org>

commit 17858b140bf49961b71d4e73f1c3ea9bc8e7dda0 upstream.

ecdh_set_secret() casts a void* pointer to a const u64* in order to
feed it into ecc_is_key_valid(). This is not generally permitted by
the C standard, and leads to actual misalignment faults on ARMv6
cores. In some cases, these are fixed up in software, but this still
leads to performance hits that are entirely avoidable.

So let's copy the key into the ctx buffer first, which we will do
anyway in the common case, and which guarantees correct alignment.

Cc: <stable@...r.kernel.org>
Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
Signed-off-by: Herbert Xu <herbert@...dor.apana.org.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 crypto/ecdh.c |    9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

--- a/crypto/ecdh.c
+++ b/crypto/ecdh.c
@@ -53,12 +53,13 @@ static int ecdh_set_secret(struct crypto
 		return ecc_gen_privkey(ctx->curve_id, ctx->ndigits,
 				       ctx->private_key);
 
-	if (ecc_is_key_valid(ctx->curve_id, ctx->ndigits,
-			     (const u64 *)params.key, params.key_size) < 0)
-		return -EINVAL;
-
 	memcpy(ctx->private_key, params.key, params.key_size);
 
+	if (ecc_is_key_valid(ctx->curve_id, ctx->ndigits,
+			     ctx->private_key, params.key_size) < 0) {
+		memzero_explicit(ctx->private_key, params.key_size);
+		return -EINVAL;
+	}
 	return 0;
 }