linux-kernel - Re: [PATCH 2/2] crypto: Remove unnecessary memzero

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Message-ID: <efd6ceb1f182aa7364e9706422768a1c1335aee4.camel@perches.com>
Date:   Mon, 13 Apr 2020 14:31:32 -0700
From:   Joe Perches <joe@...ches.com>
To:     Waiman Long <longman@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Howells <dhowells@...hat.com>,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Matthew Wilcox <willy@...radead.org>,
        David Rientjes <rientjes@...gle.com>
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        linux-kernel@...r.kernel.org, x86@...nel.org,
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Subject: Re: [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) ?