Commit f3569fd6 authored by Kees Cook's avatar Kees Cook Committed by Herbert Xu
Browse files

crypto: shash - Remove VLA usage in unaligned hashing 

In the quest to remove all stack VLA usage from the kernel[1], this uses
the newly defined max alignment to perform unaligned hashing to avoid
VLAs, and drops the helper function while adding sanity checks on the
resulting buffer sizes. Additionally, the __aligned_largest macro is
removed since this helper was the only user.

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



Signed-off-by: default avatarKees Cook <keescook@chromium.org>
Signed-off-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
parent 1299c9cf

crypto/shash.c

+16 −11
Original line number Diff line number Diff line
@@ -73,13 +73,6 @@ int crypto_shash_setkey(struct crypto_shash *tfm, const u8 *key, 
}

EXPORT_SYMBOL_GPL(crypto_shash_setkey);



static inline unsigned int shash_align_buffer_size(unsigned len,

						   unsigned long mask)

{

	typedef u8 __aligned_largest u8_aligned;

	return len + (mask & ~(__alignof__(u8_aligned) - 1));

}



static int shash_update_unaligned(struct shash_desc *desc, const u8 *data,

				  unsigned int len)

{
@@ -88,11 +81,17 @@ static int shash_update_unaligned(struct shash_desc *desc, const u8 *data, 
	unsigned long alignmask = crypto_shash_alignmask(tfm);

	unsigned int unaligned_len = alignmask + 1 -

				     ((unsigned long)data & alignmask);

	u8 ubuf[shash_align_buffer_size(unaligned_len, alignmask)]

		__aligned_largest;

	/*

	 * We cannot count on __aligned() working for large values:

	 * https://patchwork.kernel.org/patch/9507697/

	 */

	u8 ubuf[MAX_ALGAPI_ALIGNMASK * 2];

	u8 *buf = PTR_ALIGN(&ubuf[0], alignmask + 1);

	int err;



	if (WARN_ON(buf + unaligned_len > ubuf + sizeof(ubuf)))

		return -EINVAL;



	if (unaligned_len > len)

		unaligned_len = len;
@@ -124,11 +123,17 @@ static int shash_final_unaligned(struct shash_desc *desc, u8 *out) 
	unsigned long alignmask = crypto_shash_alignmask(tfm);

	struct shash_alg *shash = crypto_shash_alg(tfm);

	unsigned int ds = crypto_shash_digestsize(tfm);

	u8 ubuf[shash_align_buffer_size(ds, alignmask)]

		__aligned_largest;

	/*

	 * We cannot count on __aligned() working for large values:

	 * https://patchwork.kernel.org/patch/9507697/

	 */

	u8 ubuf[MAX_ALGAPI_ALIGNMASK + HASH_MAX_DIGESTSIZE];

	u8 *buf = PTR_ALIGN(&ubuf[0], alignmask + 1);

	int err;



	if (WARN_ON(buf + ds > ubuf + sizeof(ubuf)))

		return -EINVAL;



	err = shash->final(desc, buf);

	if (err)

		goto out;

include/linux/compiler_types.h

+0 −1
Original line number Diff line number Diff line
@@ -198,7 +198,6 @@ struct ftrace_likely_data { 
 */

#define __pure			__attribute__((pure))

#define __aligned(x)		__attribute__((aligned(x)))

#define __aligned_largest	__attribute__((aligned))

#define __printf(a, b)		__attribute__((format(printf, a, b)))

#define __scanf(a, b)		__attribute__((format(scanf, a, b)))

#define __maybe_unused		__attribute__((unused))

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