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FROMLIST: crypto: shash - stop comparing function pointers to avoid breaking CFI

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crypto_shash_alg_has_setkey() is implemented by testing whether the
.setkey() member of a struct shash_alg points to the default version
called shash_no_setkey(). As crypto_shash_alg_has_setkey() is a static
inline, this requires shash_no_setkey() to be exported to modules.

Unfortunately, when building with CFI, function pointers are routed
via CFI stubs which are private to each module (or to the kernel proper)
and so this function pointer comparison may fail spuriously.

Let's fix this by turning crypto_shash_alg_has_setkey() into an out of
line function, which makes the problem go away.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Bug: 153614920
Bug: 188620248
Link: https://lore.kernel.org/linux-crypto/20210610062150.212779-1-ardb@kernel.org
Change-Id: Ib94d812e2668020144bf8246ddbbc8b652cdf2b7
Signed-off-by: Ard Biesheuvel <ardb@google.com>
This commit is contained in:
Ard Biesheuvel
2021-06-04 21:00:09 +02:00
committed by Ard Biesheuvel
parent 254da9ba36
commit 0672a69424
2 changed files with 16 additions and 10 deletions
Download Patch File Download Diff File Expand all files Collapse all files

18
crypto/shash.c
View File

@@ -20,12 +20,24 @@
static const struct crypto_type crypto_shash_type;
int shash_no_setkey(struct crypto_shash *tfm, const u8 *key,
unsigned int keylen)
static int shash_no_setkey(struct crypto_shash *tfm, const u8 *key,
unsigned int keylen)
{
return -ENOSYS;
}
EXPORT_SYMBOL_GPL(shash_no_setkey);
/*
* Check whether an shash algorithm has a setkey function.
*
* For CFI compatibility, this must not be an inline function. This is because
* when CFI is enabled, modules won't get the same address for shash_no_setkey
* (if it were exported, which inlining would require) as the core kernel will.
*/
bool crypto_shash_alg_has_setkey(struct shash_alg *alg)
{
return alg->setkey != shash_no_setkey;
}
EXPORT_SYMBOL_GPL(crypto_shash_alg_has_setkey);
static int shash_setkey_unaligned(struct crypto_shash *tfm, const u8 *key,
unsigned int keylen)

8
include/crypto/internal/hash.h
View File

@@ -75,13 +75,7 @@ void crypto_unregister_ahashes(struct ahash_alg *algs, int count);
int ahash_register_instance(struct crypto_template *tmpl,
struct ahash_instance *inst);
int shash_no_setkey(struct crypto_shash *tfm, const u8 *key,
unsigned int keylen);
static inline bool crypto_shash_alg_has_setkey(struct shash_alg *alg)
{
return alg->setkey != shash_no_setkey;
}
bool crypto_shash_alg_has_setkey(struct shash_alg *alg);
static inline bool crypto_shash_alg_needs_key(struct shash_alg *alg)
{