2020-02-21 16:55:34

by Torsten Duwe

Subject: s390 crypto: explicitly memzero stack key material in aes_s390.c

From: Torsten Duwe <[email protected]>

s390 crypto: explicitly memzero stack key material in aes_s390.c

aes_s390.c has several functions which allocate space for key material on
the stack and leave the used keys there. It is considered good practice
to clean these locations before the function returns.

Signed-off-by: Torsten Duwe <[email protected]>
---
This popped up during our FIPS certification.
It's obviously a good idea not to leave key material on the stack.

--- a/arch/s390/crypto/aes_s390.c
+++ b/arch/s390/crypto/aes_s390.c
@@ -392,6 +392,7 @@ static int cbc_aes_crypt(struct blkciphe
ret = blkcipher_walk_done(desc, walk, nbytes - n);
}
memcpy(walk->iv, param.iv, AES_BLOCK_SIZE);
+ memzero_explicit(&param, sizeof(param));
return ret;
}

@@ -576,6 +577,8 @@ static int xts_aes_crypt(struct blkciphe
walk->dst.virt.addr, walk->src.virt.addr, n);
ret = blkcipher_walk_done(desc, walk, nbytes - n);
}
+ memzero_explicit(&pcc_param, sizeof(pcc_param));
+ memzero_explicit(&xts_param, sizeof(xts_param));
return ret;
}

2020-02-25 15:01:15

by Harald Freudenberger

Subject: Re: s390 crypto: explicitly memzero stack key material in aes_s390.c

On 21.02.20 17:55, Torsten Duwe wrote:
> From: Torsten Duwe <[email protected]>
>
> s390 crypto: explicitly memzero stack key material in aes_s390.c
>
> aes_s390.c has several functions which allocate space for key material on
> the stack and leave the used keys there. It is considered good practice
> to clean these locations before the function returns.
>
> Signed-off-by: Torsten Duwe <[email protected]>
> ---
> This popped up during our FIPS certification.
> It's obviously a good idea not to leave key material on the stack.
>
> --- a/arch/s390/crypto/aes_s390.c
> +++ b/arch/s390/crypto/aes_s390.c
> @@ -392,6 +392,7 @@ static int cbc_aes_crypt(struct blkciphe
> ret = blkcipher_walk_done(desc, walk, nbytes - n);
> }
> memcpy(walk->iv, param.iv, AES_BLOCK_SIZE);
> + memzero_explicit(&param, sizeof(param));
> return ret;
> }
>
> @@ -576,6 +577,8 @@ static int xts_aes_crypt(struct blkciphe
> walk->dst.virt.addr, walk->src.virt.addr, n);
> ret = blkcipher_walk_done(desc, walk, nbytes - n);
> }
> + memzero_explicit(&pcc_param, sizeof(pcc_param));
> + memzero_explicit(&xts_param, sizeof(xts_param));
> return ret;
> }
>
>
Thanks Torsten, I've picked this patch. It will go upstream via the s390 subsystem with the next kernel merge window.
regards Harald Freudenberger