Linux Virtualization - Apr 2020 - [PATCH 2/2] crypto: Remove unnecessary memzero_explicit()

On Mon, 2020-04-13 at 17:15 -0400, Waiman Long wrote:
> Since kfree_sensitive() will do an implicit memzero_explicit(), there
> is no need to call memzero_explicit() before it. Eliminate those
> memzero_explicit() and simplify the call sites.
2 bits of trivia:
> diff --git a/drivers/crypto/allwinner/sun8i-ce/sun8i-ce-cipher.c
b/drivers/crypto/allwinner/sun8i-ce/sun8i-ce-cipher.c
[]
> @@ -391,10 +388,7 @@ int sun8i_ce_aes_setkey(struct crypto_skcipher *tfm,
const u8 *key,
>  		dev_dbg(ce->dev, "ERROR: Invalid keylen %u\n", keylen);
>  		return -EINVAL;
>  	}
> -	if (op->key) {
> -		memzero_explicit(op->key, op->keylen);
> -		kfree(op->key);
> -	}
> +	kfree_sensitive(op->key);
>  	op->keylen = keylen;
>  	op->key = kmemdup(key, keylen, GFP_KERNEL | GFP_DMA);
>  	if (!op->key)
It might be a defect to set op->keylen before the kmemdup succeeds.
> @@ -416,10 +410,7 @@ int sun8i_ce_des3_setkey(struct crypto_skcipher *tfm,
const u8 *key,
>  	if (err)
>  		return err;
>  
> -	if (op->key) {
> -		memzero_explicit(op->key, op->keylen);
> -		kfree(op->key);
> -	}
> +	free_sensitive(op->key, op->keylen);
Why not kfree_sensitive(op->key) ?

On 4/13/20 5:31 PM, Joe Perches wrote:
> On Mon, 2020-04-13 at 17:15 -0400, Waiman Long wrote:
>> Since kfree_sensitive() will do an implicit memzero_explicit(), there
>> is no need to call memzero_explicit() before it. Eliminate those
>> memzero_explicit() and simplify the call sites.
> 2 bits of trivia:
>
>> diff --git a/drivers/crypto/allwinner/sun8i-ce/sun8i-ce-cipher.c
b/drivers/crypto/allwinner/sun8i-ce/sun8i-ce-cipher.c
> []
>> @@ -391,10 +388,7 @@ int sun8i_ce_aes_setkey(struct crypto_skcipher
*tfm, const u8 *key,
>>  		dev_dbg(ce->dev, "ERROR: Invalid keylen %u\n", keylen);
>>  		return -EINVAL;
>>  	}
>> -	if (op->key) {
>> -		memzero_explicit(op->key, op->keylen);
>> -		kfree(op->key);
>> -	}
>> +	kfree_sensitive(op->key);
>>  	op->keylen = keylen;
>>  	op->key = kmemdup(key, keylen, GFP_KERNEL | GFP_DMA);
>>  	if (!op->key)
> It might be a defect to set op->keylen before the kmemdup succeeds.
It could be. I can move it down after the op->key
check.
>> @@ -416,10 +410,7 @@ int sun8i_ce_des3_setkey(struct crypto_skcipher
*tfm, const u8 *key,
>>  	if (err)
>>  		return err;
>>  
>> -	if (op->key) {
>> -		memzero_explicit(op->key, op->keylen);
>> -		kfree(op->key);
>> -	}
>> +	free_sensitive(op->key, op->keylen);
> Why not kfree_sensitive(op->key) ?
Oh, it is a bug. I will send out v2 to fix that.

Thanks for spotting it.

Cheers,
Longman

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