From: Laszlo Ersek Subject: Re: [PATCH RESEND] hwrng: core - don't pass stack allocated buffer to rng->read() Date: Fri, 21 Oct 2016 23:34:08 +0200 Message-ID: <3c20ee42-09ff-6fa2-1915-bedd6c7be456@redhat.com> References: <20161021204809.14068-1-lersek@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Cc: linux-crypto@vger.kernel.org, "linux-kernel@vger.kernel.org" , "Richard W.M. Jones" , stable , Amit Shah , Andy Lutomirski , Herbert Xu , Kees Cook , Matt Mackall To: Andy Lutomirski Return-path: Received: from mx1.redhat.com ([209.132.183.28]:42386 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933445AbcJUVeN (ORCPT ); Fri, 21 Oct 2016 17:34:13 -0400 In-Reply-To: Sender: linux-crypto-owner@vger.kernel.org List-ID: On 10/21/16 23:04, Andy Lutomirski wrote: > On Fri, Oct 21, 2016 at 1:48 PM, Laszlo Ersek 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