linux-kernel - [PATCH v3 7/9] crypto alg: Introduce generic max blocksize and alignmask

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Message-Id: <20180629002843.31095-8-keescook@chromium.org>
Date:   Thu, 28 Jun 2018 17:28:41 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Herbert Xu <herbert@...dor.apana.org.au>
Cc:     Kees Cook <keescook@...omium.org>,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        Arnd Bergmann <arnd@...db.de>,
        Eric Biggers <ebiggers@...gle.com>,
        Alasdair Kergon <agk@...hat.com>,
        Giovanni Cabiddu <giovanni.cabiddu@...el.com>,
        Lars Persson <larper@...s.com>,
        Mike Snitzer <snitzer@...hat.com>,
        Rabin Vincent <rabinv@...s.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        "David S. Miller" <davem@...emloft.net>,
        linux-crypto@...r.kernel.org, qat-linux@...el.com,
        dm-devel@...hat.com, linux-kernel@...r.kernel.org
Subject: [PATCH v3 7/9] crypto alg: Introduce generic max blocksize and alignmask

In the quest to remove all stack VLA usage from the kernel[1], this
exposes a new general upper bound on crypto blocksize and alignmask
(higher than for the existing cipher limits) for VLA removal,
and introduces new checks.

At present, the highest cra_alignmask in the kernel is 63. The highest
cra_blocksize is 144 (SHA3_224_BLOCK_SIZE, 18 8-byte words). For the
new blocksize limit, I went with 160 (20 8-byte words).

[1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com

Signed-off-by: Kees Cook <keescook@...omium.org>
---
 crypto/algapi.c         | 7 ++++++-
 include/crypto/algapi.h | 4 +++-
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/crypto/algapi.c b/crypto/algapi.c
index c0755cf4f53f..496fc51bf215 100644
--- a/crypto/algapi.c
+++ b/crypto/algapi.c
@@ -57,9 +57,14 @@ static int crypto_check_alg(struct crypto_alg *alg)
 	if (alg->cra_alignmask & (alg->cra_alignmask + 1))
 		return -EINVAL;
 
-	if (alg->cra_blocksize > PAGE_SIZE / 8)
+	/* General maximums for all algs. */
+	if (alg->cra_alignmask > MAX_ALGAPI_ALIGNMASK)
 		return -EINVAL;
 
+	if (alg->cra_blocksize > MAX_ALGAPI_BLOCKSIZE)
+		return -EINVAL;
+
+	/* Lower maximums for specific alg types. */
 	if (!alg->cra_type && (alg->cra_flags & CRYPTO_ALG_TYPE_MASK) ==
 			       CRYPTO_ALG_TYPE_CIPHER) {
 		if (alg->cra_alignmask > MAX_CIPHER_ALIGNMASK)
diff --git a/include/crypto/algapi.h b/include/crypto/algapi.h
index bd5e8ccf1687..21371ac8f355 100644
--- a/include/crypto/algapi.h
+++ b/include/crypto/algapi.h
@@ -20,8 +20,10 @@
 /*
  * Maximum values for blocksize and alignmask, used to allocate
  * static buffers that are big enough for any combination of
- * ciphers and architectures.
+ * algs and architectures. Ciphers have a lower maximum size.
  */
+#define MAX_ALGAPI_BLOCKSIZE		160
+#define MAX_ALGAPI_ALIGNMASK		63
 #define MAX_CIPHER_BLOCKSIZE		16
 #define MAX_CIPHER_ALIGNMASK		15
 
-- 
2.17.1