On Fri, May 06, 2022 at 10:54:07AM +0100, Giovanni Cabiddu wrote:
On Fri, May 06, 2022 at 11:22:39AM +0200, Greg KH wrote:
On Fri, May 06, 2022 at 09:23:25AM +0100, Giovanni Cabiddu wrote:
Use memzero_explicit(), instead of a memset(.., 0, ..) in the implementation of the algorithms, for buffers containing sensitive information to ensure they are wiped out before free.
Cc: stable@vger.kernel.org Signed-off-by: Giovanni Cabiddu giovanni.cabiddu@intel.com Reviewed-by: Adam Guerin adam.guerin@intel.com Reviewed-by: Wojciech Ziemba wojciech.ziemba@intel.com
drivers/crypto/qat/qat_common/qat_algs.c | 20 +++++++++---------- drivers/crypto/qat/qat_common/qat_asym_algs.c | 20 +++++++++---------- 2 files changed, 20 insertions(+), 20 deletions(-)
diff --git a/drivers/crypto/qat/qat_common/qat_algs.c b/drivers/crypto/qat/qat_common/qat_algs.c index 873533dc43a7..c42df18e02b2 100644 --- a/drivers/crypto/qat/qat_common/qat_algs.c +++ b/drivers/crypto/qat/qat_common/qat_algs.c @@ -637,12 +637,12 @@ static int qat_alg_aead_newkey(struct crypto_aead *tfm, const u8 *key, return 0; out_free_all:
- memset(ctx->dec_cd, 0, sizeof(struct qat_alg_cd));
- memzero_explicit(ctx->dec_cd, sizeof(struct qat_alg_cd));
This is for structure fields, why does memset() not work properly here? The compiler should always call this, it doesn't know what dma_free_coherent() does. You are referencing this pointer after the memset() call so all should be working as intended here.
Because of this, I don't see why this change is needed. Do you have reports of compilers not calling memset() for all of this properly?
Apologies, I had a wrong assumption. Based on a comment in the memzero_explicit() documentation I assumed it should be always used to zero sensitive data.
* memzero_explicit - Fill a region of memory (e.g. sensitive * keying data) with 0s.
Yes, that's what it is for, when the compiler thinks it is "smarter than you" for stack variables.
It's great for functions like this: int foo(...) { struct key secret_key;
do something and set secret_key...
/* All done, clean up and return */ memset(&secret_key, 0, sizeof(secret_key)); return 0; }
For that, some compilers now go "hey, they just want to set this to 0 and then never touch it again, that is pointless, let's not call memset() at all!".
But when you call: memset(foo->key, 0, sizeof(key)); do_something_with_foo(foo);
the compiler can NOT go and ignore the call to memset() as it does not know what do_something_with_foo() does. Or at least it better not.
Try out this with a small example and look at the asm output for proof.
You aren't the first to be confused about this, I see this happening at least once a month with a patch to change code like you did. Don't know why it keeps coming up, is this a checkpatch() recommentation?
thanks,
greg k-h