Received-SPF: pass (google.com: domain of linux-crypto-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Thu, 10 Jun 2021 11:48:04 -0700
From:   Eric Biggers <ebiggers@kernel.org>
To:     Ard Biesheuvel <ardb@kernel.org>
Cc:     linux-crypto@vger.kernel.org, herbert@gondor.apana.org.au,
        Sami Tolvanen <samitolvanen@google.com>
Subject: Re: [PATCH v3] crypto: shash - avoid comparing pointers to exported
 functions under CFI
Message-ID: <YMJeZMiRW7Xjo/sZ@gmail.com>
References: <20210610062150.212779-1-ardb@kernel.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20210610062150.212779-1-ardb@kernel.org>
Precedence: bulk

On Thu, Jun 10, 2021 at 08:21:50AM +0200, Ard Biesheuvel wrote:
> crypto_shash_alg_has_setkey() is implemented by testing whether the
> .setkey() member of a struct shash_alg points to the default version,
> called shash_no_setkey(). As crypto_shash_alg_has_setkey() is a static
> inline, this requires shash_no_setkey() to be exported to modules.
> 
> Unfortunately, when building with CFI, function pointers are routed
> via CFI stubs which are private to each module (or to the kernel proper)
> and so this function pointer comparison may fail spuriously.
> 
> Let's fix this by turning crypto_shash_alg_has_setkey() into an out of
> line function.
> 
> Cc: Sami Tolvanen <samitolvanen@google.com>
> Cc: Eric Biggers <ebiggers@kernel.org>
> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> ---
> v3: improve comment as per Eric's suggestion
> v2: add code comment to explain why the function needs to remain out of
> line
> 
>  crypto/shash.c                 | 18 +++++++++++++++---
>  include/crypto/internal/hash.h |  8 +-------
>  2 files changed, 16 insertions(+), 10 deletions(-)
> 

Reviewed-by: Eric Biggers <ebiggers@google.com>