From 17858b140bf49961b71d4e73f1c3ea9bc8e7dda0 Mon Sep 17 00:00:00 2001
From: Ard Biesheuvel <ardb@kernel.org>
Date: Tue, 24 Nov 2020 11:47:19 +0100
Subject: [PATCH] crypto: ecdh - avoid unaligned accesses in ecdh_set_secret()
Git-commit: 17858b140bf49961b71d4e73f1c3ea9bc8e7dda0
Patch-mainline: v5.11-rc1
References: git-fixes

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@vger.kernel.org>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Acked-by: Takashi Iwai <tiwai@suse.de>

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

diff --git a/crypto/ecdh.c b/crypto/ecdh.c
index b0232d6ab4ce..d56b8603dec9 100644
--- a/crypto/ecdh.c
+++ b/crypto/ecdh.c
@@ -53,12 +53,13 @@ static int ecdh_set_secret(struct crypto_kpp *tfm, const void *buf,
 		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;
 }
 
-- 
2.26.2