linux-kernel - Re: [PATCH v4 02/29] rxrpc: Avoid using stack memory in SG lists in rxkad

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Message-ID: <20160628094522.GB16467@gondor.apana.org.au>
Date:	Tue, 28 Jun 2016 17:45:22 +0800
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	David Howells <dhowells@...hat.com>
Cc:	Andy Lutomirski <luto@...nel.org>, x86@...nel.org,
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	Borislav Petkov <bp@...en8.de>,
	Nadav Amit <nadav.amit@...il.com>,
	Kees Cook <keescook@...omium.org>,
	Brian Gerst <brgerst@...il.com>,
	"kernel-hardening@...ts.openwall.com" 
	<kernel-hardening@...ts.openwall.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Josh Poimboeuf <jpoimboe@...hat.com>,
	Jann Horn <jann@...jh.net>,
	Heiko Carstens <heiko.carstens@...ibm.com>
Subject: Re: [PATCH v4 02/29] rxrpc: Avoid using stack memory in SG lists in
 rxkad

On Tue, Jun 28, 2016 at 10:07:44AM +0100, David Howells wrote:
>
> Since it's (more or less) a one off piece of memory, why not kmalloc it
> temporarily rather than expanding the connection struct?  Also, the bit where
> you put a second rxrpc_crypt in just so that it happens to give you a 16-byte
> slot by adjacency is pretty icky.  It would be much better to use a union
> instead:
> 
> 	union {
> 		struct rxrpc_crypt	csum_iv; /* packet checksum base */
> 		__be32 tmpbuf[4];
> 	};

Feel free to send your own patch to do this.

> Note also that the above doesn't guarantee that the struct will be inside of a
> single page.  It would need an alignment of 16 for that - but you only have
> one sg.  Could that be a problem?

No it's not a problem.
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt