netdev - Re: [RFC PATCH] rxrpc: Fix -Wframe-larger-than= warnings from on-stack crypto

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Date:   Thu, 25 Jul 2019 16:43:47 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     David Howells <dhowells@...hat.com>
Cc:     linux-afs@...ts.infradead.org,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "open list:HARDWARE RANDOM NUMBER GENERATOR CORE" 
        <linux-crypto@...r.kernel.org>, Networking <netdev@...r.kernel.org>
Subject: Re: [RFC PATCH] rxrpc: Fix -Wframe-larger-than= warnings from
 on-stack crypto

On Thu, Jul 25, 2019 at 3:31 PM David Howells <dhowells@...hat.com> wrote:
>
> rxkad sometimes triggers a warning about oversized stack frames when
> building with clang for a 32-bit architecture:
>
> net/rxrpc/rxkad.c:243:12: error: stack frame size of 1088 bytes in function 'rxkad_secure_packet' [-Werror,-Wframe-larger-than=]
> net/rxrpc/rxkad.c:501:12: error: stack frame size of 1088 bytes in function 'rxkad_verify_packet' [-Werror,-Wframe-larger-than=]
>
> The problem is the combination of SYNC_SKCIPHER_REQUEST_ON_STACK() in
> rxkad_verify_packet()/rxkad_secure_packet() with the relatively large
> scatterlist in rxkad_verify_packet_1()/rxkad_secure_packet_encrypt().
>
> The warning does not show up when using gcc, which does not inline the
> functions as aggressively, but the problem is still the same.
>
> Allocate the cipher buffers from the slab instead, caching the allocated
> packet crypto request memory used for DATA packet crypto in the rxrpc_call
> struct.
>
> Fixes: 17926a79320a ("[AF_RXRPC]: Provide secure RxRPC sockets for use by userspace and kernel both")
> Reported-by: Arnd Bergmann <arnd@...db.de>
> Signed-off-by: David Howells <dhowells@...hat.com>
> cc: Herbert Xu <herbert@...dor.apana.org.au>

Acked-by: Arnd Bergmann <arnd@...db.de>