From: Yisheng Xie Subject: Re: [PATCH resend 4.9] hw_random: Don't use a stack buffer in add_early_randomness() Date: Sat, 4 Feb 2017 11:47:38 +0800 Message-ID: References: <4169224b6858d1cf149f1a73f8a03603fa19076d.1476638125.git.luto@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset="windows-1252" Content-Transfer-Encoding: 7bit Cc: Jens Axboe , Matt Mullins , Xishi Qiu , Hanjun Guo To: Andy Lutomirski , , , Matt Mackall , Herbert Xu , Rusty Russell Return-path: Received: from szxga03-in.huawei.com ([119.145.14.66]:33213 "EHLO szxga03-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753413AbdBDDr6 (ORCPT ); Fri, 3 Feb 2017 22:47:58 -0500 In-Reply-To: <4169224b6858d1cf149f1a73f8a03603fa19076d.1476638125.git.luto@kernel.org> Sender: linux-crypto-owner@vger.kernel.org List-ID: Hi Andy, On 2016/10/18 1:06, Andy Lutomirski wrote: > hw_random carefully avoids using a stack buffer except in > add_early_randomness(). This causes a crash in virtio_rng if > CONFIG_VMAP_STACK=y. I try to understand this patch, but I do not know why it will cause a crash in virtio_rng with CONFIG_VMAP_STACK=y? Could you please give me more info. about it. Really thanks for that! Yisheng Xie. > > Reported-by: Matt Mullins > Tested-by: Matt Mullins > Fixes: d3cc7996473a ("hwrng: fetch randomness only after device init") > Signed-off-by: Andy Lutomirski > --- > > This fixes a crash in 4.9-rc1. > > resending because I typoed the git send-email command. I stealthily added > Matt's Tested-by, too. > > drivers/char/hw_random/core.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c > index 9203f2d130c0..340f96e44642 100644 > --- a/drivers/char/hw_random/core.c > +++ b/drivers/char/hw_random/core.c > @@ -84,14 +84,14 @@ static size_t rng_buffer_size(void) > > static void add_early_randomness(struct hwrng *rng) > { > - unsigned char bytes[16]; > int bytes_read; > + size_t size = min_t(size_t, 16, rng_buffer_size()); > > mutex_lock(&reading_mutex); > - bytes_read = rng_get_data(rng, bytes, sizeof(bytes), 1); > + bytes_read = rng_get_data(rng, rng_buffer, size, 1); > mutex_unlock(&reading_mutex); > if (bytes_read > 0) > - add_device_randomness(bytes, bytes_read); > + add_device_randomness(rng_buffer, bytes_read); > } > > static inline void cleanup_rng(struct kref *kref) >