From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:50783) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gUuDd-000078-Ai for qemu-devel@nongnu.org; Thu, 06 Dec 2018 09:01:37 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1gUuAT-00043w-N3 for qemu-devel@nongnu.org; Thu, 06 Dec 2018 08:58:22 -0500 Received: from mx1.redhat.com ([209.132.183.28]:40074) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1gUuAT-000420-G7 for qemu-devel@nongnu.org; Thu, 06 Dec 2018 08:58:17 -0500 Date: Thu, 6 Dec 2018 08:58:08 -0500 From: "Michael S. Tsirkin" Message-ID: <20181206085609-mutt-send-email-mst@kernel.org> References: <20181206121830.6177-1-ppandit@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181206121830.6177-1-ppandit@redhat.com> Subject: Re: [Qemu-devel] [PATCH v1] i2c: pm_smbus: check smb_index before block transfer write List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: P J P Cc: Qemu Developers , Paolo Bonzini , Michael Hanselmann , Peter Maydell , Igor Mammedov , Prasad J Pandit On Thu, Dec 06, 2018 at 05:48:30PM +0530, P J P wrote: > From: Prasad J Pandit > > While performing block transfer write in smb_ioport_writeb(), > 'smb_index' is incremented and used to index smb_data[] array. > Check 'smb_index' value to avoid OOB access. > > Note that this bug is exploitable by a guest to escape > from the virtual machine. However the commit which > introduced the bug was only made after the 3.0 release, > and so it is not present in any released QEMU versions. > > Fixes: 38ad4fae43 i2c: pm_smbus: Add block transfer capability > Reported-by: Michael Hanselmann > Signed-off-by: Prasad J Pandit Reviewed-by: Michael S. Tsirkin > --- > hw/i2c/pm_smbus.c | 3 +++ > 1 file changed, 3 insertions(+) > > Update v1: add note about issue being introduced after 3.0 release > -> https://lists.gnu.org/archive/html/qemu-devel/2018-12/msg01115.html > > diff --git a/hw/i2c/pm_smbus.c b/hw/i2c/pm_smbus.c > index 685a2378ed..03062740cc 100644 > --- a/hw/i2c/pm_smbus.c > +++ b/hw/i2c/pm_smbus.c > @@ -240,6 +240,9 @@ static void smb_ioport_writeb(void *opaque, hwaddr addr, uint64_t val, > uint8_t read = s->smb_addr & 0x01; > > s->smb_index++; > + if (s->smb_index >= PM_SMBUS_MAX_MSG_SIZE) { > + s->smb_index = 0; > + } when I see patterns like these I always think "what about spectre". But not a new issue and not the only place, so we can leave this for another day. > if (!read && s->smb_index == s->smb_data0) { > uint8_t prot = (s->smb_ctl >> 2) & 0x07; > uint8_t cmd = s->smb_cmd; > -- > 2.19.2