From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 32B12C61DB3 for ; Mon, 9 Jan 2023 15:12:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=9R9Fzmuc/mQHIMYYHceufnmOvemwRV164Iefng6OCnQ=; b=080h1SyGpsniYB /nywInhPK8JAW8LPr5MTHzSw1Z1aTC0YIyWQ9Kv13gOch97Oo4EfLYorP3Dd61SzCb3FSyP7Ed803 zwVhnHhQL3jzDCsJXHnn1G3PET9BJ2b0WTMcokCinxQo6Zdg8ZGZCakGn5ZP73GP36PFcS/oArG7N Epda3uoyJ7EZ/GRBh8INASeUBcUQhufbidC7JFMFLnae8YV88bjlKbqUgd1DNvHbkfW7TpnPLpWVc ihM8V8G6M8cxhQG+JjuDl6wGTcz7EVPfkM6ubAUwLtKchVTcYynduPDn3S6mzXi5q9Bq7erSXM1FW yAUuyFgVGVqjIMvHIIOA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1pEtnr-0027s5-5k; Mon, 09 Jan 2023 15:11:11 +0000 Received: from ams.source.kernel.org ([145.40.68.75]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1pEtnm-0027q3-TP for linux-arm-kernel@lists.infradead.org; Mon, 09 Jan 2023 15:11:09 +0000 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 6874FB80E1A; Mon, 9 Jan 2023 15:11:02 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7380BC433EF; Mon, 9 Jan 2023 15:10:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1673277061; bh=odY6QjAbOvpE7fHaT+Q/JFKRR8E2t90LcaafBvzc4W0=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=mw5vM2quubu22s1JORyeWyqPGh+IFo4df8FnVD/XVuM8TLGCIEtEg1uCfjTh2i3U5 Bh5uotDxycU8iB52xJvp2faVd4CA8ije0kWNxCuIdA6ZnBfxFjsUqxBrNAZMKwcJyO bJVetnpOW/JOGsv9T0gFfiolE3NLJKgeUV2qKezr3oJzMe3wCuTISpnqBeyVyKIQpo nNElhF3/fGT5kCW7p1GfADdvVj2WOG7arQkzt6ezno4PkjudnK+qE/saeLk0NRymuG VhUzuZ8kOwILOHwbecS+oJLnfpRPg35TrEusfOX4+PrTgqUGpXf/zmVdCKf/uLCz+Y hJ2iwjIWGTRZg== Date: Mon, 9 Jan 2023 15:10:55 +0000 From: Will Deacon To: Ard Biesheuvel Cc: linux-arm-kernel@lists.infradead.org, linux-efi@vger.kernel.org, catalin.marinas@arm.com, stable@vger.kernel.org, Peter Jones , Jarkko Sakkinen , Matthew Garrett , Nathan Chancellor Subject: Re: [PATCH] efi: tpm: Avoid READ_ONCE() for accessing the event log Message-ID: <20230109151054.GA7817@willie-the-truck> References: <20230109095948.2471205-1-ardb@kernel.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20230109095948.2471205-1-ardb@kernel.org> User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20230109_071107_622516_582FCA7D X-CRM114-Status: GOOD ( 28.56 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Mon, Jan 09, 2023 at 10:59:48AM +0100, Ard Biesheuvel wrote: > Nathan reports that recent kernels built with LTO will crash when doing > EFI boot using Fedora's GRUB and SHIM. The culprit turns out to be a > misaligned load from the TPM event log, which is annotated with > READ_ONCE(), and under LTO, this gets translated into a LDAR instruction > which does not tolerate misaligned accesses. Interesting, that's a funny change in behaviour. READ_ONCE() of an unaligned address is pretty sketchy, but if this ends up tripping lots of folks up then I suppose we could use a plain load and a DMB LD as an alternative. It's likely to be more expensive in the LDAPR case, though. > Interestingly, this does not happen when booting the same kernel > straight from the UEFI shell, and so the fact that the event log may > appear misaligned in memory may be caused by a bug in GRUB or SHIM. > > However, using READ_ONCE() to access firmware tables is slightly unusual > in any case, and here, we only need to ensure that 'event' is not > dereferenced again after it gets unmapped, so a compiler barrier should > be sufficient, and works around the reported issue. > > Cc: > Cc: Peter Jones > Cc: Jarkko Sakkinen > Cc: Matthew Garrett > Reported-by: Nathan Chancellor > Link: https://github.com/ClangBuiltLinux/linux/issues/1782 > Signed-off-by: Ard Biesheuvel > --- > include/linux/tpm_eventlog.h | 6 ++++-- > 1 file changed, 4 insertions(+), 2 deletions(-) > > diff --git a/include/linux/tpm_eventlog.h b/include/linux/tpm_eventlog.h > index 20c0ff54b7a0d313..0abcc85904cba874 100644 > --- a/include/linux/tpm_eventlog.h > +++ b/include/linux/tpm_eventlog.h > @@ -198,8 +198,10 @@ static __always_inline int __calc_tpm2_event_size(struct tcg_pcr_event2_head *ev > * The loop below will unmap these fields if the log is larger than > * one page, so save them here for reference: > */ > - count = READ_ONCE(event->count); > - event_type = READ_ONCE(event->event_type); > + count = event->count; > + event_type = event->event_type; > + > + barrier(); It would be handy to have a comment here, but when I started thinking about what that would say, it occurred to me that the unmap operation should already have a barrier inside it due to the TLB invalidation, so I'm not sure why this is needed at all. Will _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel