linux-kernel - Re: [PATCH RESEND] hwrng: core - don't pass stack allocated buffer to rng->read()

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Message-ID: <3c20ee42-09ff-6fa2-1915-bedd6c7be456@redhat.com>
Date:   Fri, 21 Oct 2016 23:34:08 +0200
From:   Laszlo Ersek <lersek@...hat.com>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     linux-crypto@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Richard W.M. Jones" <rjones@...hat.com>,
        stable <stable@...r.kernel.org>,
        Amit Shah <amit.shah@...hat.com>,
        Andy Lutomirski <luto@...nel.org>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Kees Cook <keescook@...omium.org>,
        Matt Mackall <mpm@...enic.com>
Subject: Re: [PATCH RESEND] hwrng: core - don't pass stack allocated buffer to
 rng->read()

On 10/21/16 23:04, Andy Lutomirski wrote:
> On Fri, Oct 21, 2016 at 1:48 PM, Laszlo Ersek <lersek@...hat.com> wrote:
>> The virtio-rng backend for hwrng passes the buffer that it receives for
>> filling to sg_set_buf() directly, in:
>>
>> virtio_read()       [drivers/char/hw_random/virtio-rng.c]
>>   register_buffer() [drivers/char/hw_random/virtio-rng.c]
>>     sg_init_one()   [lib/scatterlist.c]
>>       sg_set_buf()  [include/linux/scatterlist.h]
>>
>> In turn, the sg_set_buf() function, when built with CONFIG_DEBUG_SG,
>> actively enforces (justifiedly) that the buffer used within the
>> scatter-gather list live in physically contiguous memory:
>>
>>   BUG_ON(!virt_addr_valid(buf));
>>
>> The combination of the above two facts means that whatever calls
>> virtio_read() -- via the hwrng.read() method -- has to allocate the
>> recipient buffer in physically contiguous memory.
> 
> Indeed.  This bug should be fixed by:
> 
> https://git.kernel.org/cgit/linux/kernel/git/herbert/cryptodev-2.6.git/commit/?id=6d4952d9d9d4dc2bb9c0255d95a09405a1e958f7
> 

Cool, thanks!

(My commit message is better tho ;))

Cheers
Laszlo