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linux-next/include/crypto/algapi.h
James Yonan 6bf37e5aa9 crypto: crypto_memneq - add equality testing of memory regions w/o timing leaks
When comparing MAC hashes, AEAD authentication tags, or other hash
values in the context of authentication or integrity checking, it
is important not to leak timing information to a potential attacker,
i.e. when communication happens over a network.

Bytewise memory comparisons (such as memcmp) are usually optimized so
that they return a nonzero value as soon as a mismatch is found. E.g,
on x86_64/i5 for 512 bytes this can be ~50 cyc for a full mismatch
and up to ~850 cyc for a full match (cold). This early-return behavior
can leak timing information as a side channel, allowing an attacker to
iteratively guess the correct result.

This patch adds a new method crypto_memneq ("memory not equal to each
other") to the crypto API that compares memory areas of the same length
in roughly "constant time" (cache misses could change the timing, but
since they don't reveal information about the content of the strings
being compared, they are effectively benign). Iow, best and worst case
behaviour take the same amount of time to complete (in contrast to
memcmp).

Note that crypto_memneq (unlike memcmp) can only be used to test for
equality or inequality, NOT for lexicographical order. This, however,
is not an issue for its use-cases within the crypto API.

We tried to locate all of the places in the crypto API where memcmp was
being used for authentication or integrity checking, and convert them
over to crypto_memneq.

crypto_memneq is declared noinline, placed in its own source file,
and compiled with optimizations that might increase code size disabled
("Os") because a smart compiler (or LTO) might notice that the return
value is always compared against zero/nonzero, and might then
reintroduce the same early-return optimization that we are trying to
avoid.

Using #pragma or __attribute__ optimization annotations of the code
for disabling optimization was avoided as it seems to be considered
broken or unmaintained for long time in GCC [1]. Therefore, we work
around that by specifying the compile flag for memneq.o directly in
the Makefile. We found that this seems to be most appropriate.

As we use ("Os"), this patch also provides a loop-free "fast-path" for
frequently used 16 byte digests. Similarly to kernel library string
functions, leave an option for future even further optimized architecture
specific assembler implementations.

This was a joint work of James Yonan and Daniel Borkmann. Also thanks
for feedback from Florian Weimer on this and earlier proposals [2].

  [1] http://gcc.gnu.org/ml/gcc/2012-07/msg00211.html
  [2] https://lkml.org/lkml/2013/2/10/131

Signed-off-by: James Yonan <james@openvpn.net>
Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Cc: Florian Weimer <fw@deneb.enyo.de>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2013-10-07 14:17:06 +08:00

407 lines
11 KiB
C

/*
* Cryptographic API for algorithms (i.e., low-level API).
*
* Copyright (c) 2006 Herbert Xu <herbert@gondor.apana.org.au>
*
* This program is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License as published by the Free
* Software Foundation; either version 2 of the License, or (at your option)
* any later version.
*
*/
#ifndef _CRYPTO_ALGAPI_H
#define _CRYPTO_ALGAPI_H
#include <linux/crypto.h>
#include <linux/list.h>
#include <linux/kernel.h>
#include <linux/skbuff.h>
struct module;
struct rtattr;
struct seq_file;
struct crypto_type {
unsigned int (*ctxsize)(struct crypto_alg *alg, u32 type, u32 mask);
unsigned int (*extsize)(struct crypto_alg *alg);
int (*init)(struct crypto_tfm *tfm, u32 type, u32 mask);
int (*init_tfm)(struct crypto_tfm *tfm);
void (*show)(struct seq_file *m, struct crypto_alg *alg);
int (*report)(struct sk_buff *skb, struct crypto_alg *alg);
struct crypto_alg *(*lookup)(const char *name, u32 type, u32 mask);
unsigned int type;
unsigned int maskclear;
unsigned int maskset;
unsigned int tfmsize;
};
struct crypto_instance {
struct crypto_alg alg;
struct crypto_template *tmpl;
struct hlist_node list;
void *__ctx[] CRYPTO_MINALIGN_ATTR;
};
struct crypto_template {
struct list_head list;
struct hlist_head instances;
struct module *module;
struct crypto_instance *(*alloc)(struct rtattr **tb);
void (*free)(struct crypto_instance *inst);
int (*create)(struct crypto_template *tmpl, struct rtattr **tb);
char name[CRYPTO_MAX_ALG_NAME];
};
struct crypto_spawn {
struct list_head list;
struct crypto_alg *alg;
struct crypto_instance *inst;
const struct crypto_type *frontend;
u32 mask;
};
struct crypto_queue {
struct list_head list;
struct list_head *backlog;
unsigned int qlen;
unsigned int max_qlen;
};
struct scatter_walk {
struct scatterlist *sg;
unsigned int offset;
};
struct blkcipher_walk {
union {
struct {
struct page *page;
unsigned long offset;
} phys;
struct {
u8 *page;
u8 *addr;
} virt;
} src, dst;
struct scatter_walk in;
unsigned int nbytes;
struct scatter_walk out;
unsigned int total;
void *page;
u8 *buffer;
u8 *iv;
int flags;
unsigned int blocksize;
};
struct ablkcipher_walk {
struct {
struct page *page;
unsigned int offset;
} src, dst;
struct scatter_walk in;
unsigned int nbytes;
struct scatter_walk out;
unsigned int total;
struct list_head buffers;
u8 *iv_buffer;
u8 *iv;
int flags;
unsigned int blocksize;
};
extern const struct crypto_type crypto_ablkcipher_type;
extern const struct crypto_type crypto_aead_type;
extern const struct crypto_type crypto_blkcipher_type;
void crypto_mod_put(struct crypto_alg *alg);
int crypto_register_template(struct crypto_template *tmpl);
void crypto_unregister_template(struct crypto_template *tmpl);
struct crypto_template *crypto_lookup_template(const char *name);
int crypto_register_instance(struct crypto_template *tmpl,
struct crypto_instance *inst);
int crypto_unregister_instance(struct crypto_alg *alg);
int crypto_init_spawn(struct crypto_spawn *spawn, struct crypto_alg *alg,
struct crypto_instance *inst, u32 mask);
int crypto_init_spawn2(struct crypto_spawn *spawn, struct crypto_alg *alg,
struct crypto_instance *inst,
const struct crypto_type *frontend);
void crypto_drop_spawn(struct crypto_spawn *spawn);
struct crypto_tfm *crypto_spawn_tfm(struct crypto_spawn *spawn, u32 type,
u32 mask);
void *crypto_spawn_tfm2(struct crypto_spawn *spawn);
static inline void crypto_set_spawn(struct crypto_spawn *spawn,
struct crypto_instance *inst)
{
spawn->inst = inst;
}
struct crypto_attr_type *crypto_get_attr_type(struct rtattr **tb);
int crypto_check_attr_type(struct rtattr **tb, u32 type);
const char *crypto_attr_alg_name(struct rtattr *rta);
struct crypto_alg *crypto_attr_alg2(struct rtattr *rta,
const struct crypto_type *frontend,
u32 type, u32 mask);
static inline struct crypto_alg *crypto_attr_alg(struct rtattr *rta,
u32 type, u32 mask)
{
return crypto_attr_alg2(rta, NULL, type, mask);
}
int crypto_attr_u32(struct rtattr *rta, u32 *num);
void *crypto_alloc_instance2(const char *name, struct crypto_alg *alg,
unsigned int head);
struct crypto_instance *crypto_alloc_instance(const char *name,
struct crypto_alg *alg);
void crypto_init_queue(struct crypto_queue *queue, unsigned int max_qlen);
int crypto_enqueue_request(struct crypto_queue *queue,
struct crypto_async_request *request);
void *__crypto_dequeue_request(struct crypto_queue *queue, unsigned int offset);
struct crypto_async_request *crypto_dequeue_request(struct crypto_queue *queue);
int crypto_tfm_in_queue(struct crypto_queue *queue, struct crypto_tfm *tfm);
/* These functions require the input/output to be aligned as u32. */
void crypto_inc(u8 *a, unsigned int size);
void crypto_xor(u8 *dst, const u8 *src, unsigned int size);
int blkcipher_walk_done(struct blkcipher_desc *desc,
struct blkcipher_walk *walk, int err);
int blkcipher_walk_virt(struct blkcipher_desc *desc,
struct blkcipher_walk *walk);
int blkcipher_walk_phys(struct blkcipher_desc *desc,
struct blkcipher_walk *walk);
int blkcipher_walk_virt_block(struct blkcipher_desc *desc,
struct blkcipher_walk *walk,
unsigned int blocksize);
int ablkcipher_walk_done(struct ablkcipher_request *req,
struct ablkcipher_walk *walk, int err);
int ablkcipher_walk_phys(struct ablkcipher_request *req,
struct ablkcipher_walk *walk);
void __ablkcipher_walk_complete(struct ablkcipher_walk *walk);
static inline void *crypto_tfm_ctx_aligned(struct crypto_tfm *tfm)
{
return PTR_ALIGN(crypto_tfm_ctx(tfm),
crypto_tfm_alg_alignmask(tfm) + 1);
}
static inline struct crypto_instance *crypto_tfm_alg_instance(
struct crypto_tfm *tfm)
{
return container_of(tfm->__crt_alg, struct crypto_instance, alg);
}
static inline void *crypto_instance_ctx(struct crypto_instance *inst)
{
return inst->__ctx;
}
static inline struct ablkcipher_alg *crypto_ablkcipher_alg(
struct crypto_ablkcipher *tfm)
{
return &crypto_ablkcipher_tfm(tfm)->__crt_alg->cra_ablkcipher;
}
static inline void *crypto_ablkcipher_ctx(struct crypto_ablkcipher *tfm)
{
return crypto_tfm_ctx(&tfm->base);
}
static inline void *crypto_ablkcipher_ctx_aligned(struct crypto_ablkcipher *tfm)
{
return crypto_tfm_ctx_aligned(&tfm->base);
}
static inline struct aead_alg *crypto_aead_alg(struct crypto_aead *tfm)
{
return &crypto_aead_tfm(tfm)->__crt_alg->cra_aead;
}
static inline void *crypto_aead_ctx(struct crypto_aead *tfm)
{
return crypto_tfm_ctx(&tfm->base);
}
static inline struct crypto_instance *crypto_aead_alg_instance(
struct crypto_aead *aead)
{
return crypto_tfm_alg_instance(&aead->base);
}
static inline struct crypto_blkcipher *crypto_spawn_blkcipher(
struct crypto_spawn *spawn)
{
u32 type = CRYPTO_ALG_TYPE_BLKCIPHER;
u32 mask = CRYPTO_ALG_TYPE_MASK;
return __crypto_blkcipher_cast(crypto_spawn_tfm(spawn, type, mask));
}
static inline void *crypto_blkcipher_ctx(struct crypto_blkcipher *tfm)
{
return crypto_tfm_ctx(&tfm->base);
}
static inline void *crypto_blkcipher_ctx_aligned(struct crypto_blkcipher *tfm)
{
return crypto_tfm_ctx_aligned(&tfm->base);
}
static inline struct crypto_cipher *crypto_spawn_cipher(
struct crypto_spawn *spawn)
{
u32 type = CRYPTO_ALG_TYPE_CIPHER;
u32 mask = CRYPTO_ALG_TYPE_MASK;
return __crypto_cipher_cast(crypto_spawn_tfm(spawn, type, mask));
}
static inline struct cipher_alg *crypto_cipher_alg(struct crypto_cipher *tfm)
{
return &crypto_cipher_tfm(tfm)->__crt_alg->cra_cipher;
}
static inline struct crypto_hash *crypto_spawn_hash(struct crypto_spawn *spawn)
{
u32 type = CRYPTO_ALG_TYPE_HASH;
u32 mask = CRYPTO_ALG_TYPE_HASH_MASK;
return __crypto_hash_cast(crypto_spawn_tfm(spawn, type, mask));
}
static inline void *crypto_hash_ctx(struct crypto_hash *tfm)
{
return crypto_tfm_ctx(&tfm->base);
}
static inline void *crypto_hash_ctx_aligned(struct crypto_hash *tfm)
{
return crypto_tfm_ctx_aligned(&tfm->base);
}
static inline void blkcipher_walk_init(struct blkcipher_walk *walk,
struct scatterlist *dst,
struct scatterlist *src,
unsigned int nbytes)
{
walk->in.sg = src;
walk->out.sg = dst;
walk->total = nbytes;
}
static inline void ablkcipher_walk_init(struct ablkcipher_walk *walk,
struct scatterlist *dst,
struct scatterlist *src,
unsigned int nbytes)
{
walk->in.sg = src;
walk->out.sg = dst;
walk->total = nbytes;
INIT_LIST_HEAD(&walk->buffers);
}
static inline void ablkcipher_walk_complete(struct ablkcipher_walk *walk)
{
if (unlikely(!list_empty(&walk->buffers)))
__ablkcipher_walk_complete(walk);
}
static inline struct crypto_async_request *crypto_get_backlog(
struct crypto_queue *queue)
{
return queue->backlog == &queue->list ? NULL :
container_of(queue->backlog, struct crypto_async_request, list);
}
static inline int ablkcipher_enqueue_request(struct crypto_queue *queue,
struct ablkcipher_request *request)
{
return crypto_enqueue_request(queue, &request->base);
}
static inline struct ablkcipher_request *ablkcipher_dequeue_request(
struct crypto_queue *queue)
{
return ablkcipher_request_cast(crypto_dequeue_request(queue));
}
static inline void *ablkcipher_request_ctx(struct ablkcipher_request *req)
{
return req->__ctx;
}
static inline int ablkcipher_tfm_in_queue(struct crypto_queue *queue,
struct crypto_ablkcipher *tfm)
{
return crypto_tfm_in_queue(queue, crypto_ablkcipher_tfm(tfm));
}
static inline void *aead_request_ctx(struct aead_request *req)
{
return req->__ctx;
}
static inline void aead_request_complete(struct aead_request *req, int err)
{
req->base.complete(&req->base, err);
}
static inline u32 aead_request_flags(struct aead_request *req)
{
return req->base.flags;
}
static inline struct crypto_alg *crypto_get_attr_alg(struct rtattr **tb,
u32 type, u32 mask)
{
return crypto_attr_alg(tb[1], type, mask);
}
/*
* Returns CRYPTO_ALG_ASYNC if type/mask requires the use of sync algorithms.
* Otherwise returns zero.
*/
static inline int crypto_requires_sync(u32 type, u32 mask)
{
return (type ^ CRYPTO_ALG_ASYNC) & mask & CRYPTO_ALG_ASYNC;
}
noinline unsigned long __crypto_memneq(const void *a, const void *b, size_t size);
/**
* crypto_memneq - Compare two areas of memory without leaking
* timing information.
*
* @a: One area of memory
* @b: Another area of memory
* @size: The size of the area.
*
* Returns 0 when data is equal, 1 otherwise.
*/
static inline int crypto_memneq(const void *a, const void *b, size_t size)
{
return __crypto_memneq(a, b, size) != 0UL ? 1 : 0;
}
#endif /* _CRYPTO_ALGAPI_H */