From patchwork Fri Aug 19 15:50:59 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Guilherme G. Piccoli" X-Patchwork-Id: 598615 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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 55919C28B2B for ; Fri, 19 Aug 2022 15:58:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1350722AbiHSP6j (ORCPT ); Fri, 19 Aug 2022 11:58:39 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41102 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1350724AbiHSP5C (ORCPT ); Fri, 19 Aug 2022 11:57:02 -0400 Received: from fanzine2.igalia.com (fanzine.igalia.com [178.60.130.6]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1FE52108B00; Fri, 19 Aug 2022 08:51:34 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=igalia.com; s=20170329; h=Content-Transfer-Encoding:MIME-Version:Message-Id:Date:Subject: Cc:To:From:Sender:Reply-To:Content-Type:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: In-Reply-To:References:List-Id:List-Help:List-Unsubscribe:List-Subscribe: List-Post:List-Owner:List-Archive; bh=28vkizyvUtYm4/sTyN+MXhOLB0Fo0DX7lO6TnmiJ624=; b=nRKFd6buwCNbA3003YPVFxn6ZF 8IfZbIwtydC8ZU5xNGIYjRMrNlaFUnAbH4BQ0psaGBPKAQdQNodJ9aAM8tBIDYEsilzFjaOOwGY0O rURKPeOQkBy6IrMkwIE4NyAmPbUfMzLWtTFvpxK6rAHILVTNCRbWaFpTKW7moSBiRYZtYH/OV7Ytm GEA8RDpIXlNJxOeqxSNqD3BZhbjrL4fLxFQdTK7aGM3qV5pE4wvEA7xMtH7Pv4YytPq1RzsONSVNM yItfcCNT9tkveEBRM9cd2PIGqQHKtBBuoUaF9SI/sgQEoLq6TLrQnaZKjrMDfqC+5LVyQnQuJu/bd oStPx5LA==; Received: from [179.232.144.59] (helo=localhost) by fanzine2.igalia.com with esmtpsa (Cipher TLS1.3:ECDHE_SECP256R1__RSA_PSS_RSAE_SHA256__AES_256_GCM:256) (Exim) id 1oP4HM-00CNLN-Dx; Fri, 19 Aug 2022 17:51:27 +0200 From: "Guilherme G. Piccoli" To: arnd@arndb.de, gregkh@linuxfoundation.org, evgreen@chromium.org Cc: linux-efi@vger.kernel.org, linux-kernel@vger.kernel.org, gpiccoli@igalia.com, kernel@gpiccoli.net, ardb@kernel.org, davidgow@google.com, jwerner@chromium.org Subject: [PATCH V3] firmware: google: Test spinlock on panic path to avoid lockups Date: Fri, 19 Aug 2022 12:50:59 -0300 Message-Id: <20220819155059.451674-1-gpiccoli@igalia.com> X-Mailer: git-send-email 2.37.2 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-efi@vger.kernel.org Currently the gsmi driver registers a panic notifier as well as reboot and die notifiers. The callbacks registered are called in atomic and very limited context - for instance, panic disables preemption and local IRQs, also all secondary CPUs (not executing the panic path) are shutdown. With that said, taking a spinlock in this scenario is a dangerous invitation for lockup scenarios. So, fix that by checking if the spinlock is free to acquire in the panic notifier callback - if not, bail-out and avoid a potential hang. Fixes: 74c5b31c6618 ("driver: Google EFI SMI") Cc: Ard Biesheuvel Cc: David Gow Cc: Julius Werner Reviewed-by: Evan Green Signed-off-by: Guilherme G. Piccoli --- This is a re-submission of the patch - it was in a series [0], but Greg suggested me to resubmit individually in order it gets picked by the relevant maintainers, instead of asking them to merge individual patches from a series. Notice I've trimmed a bit the CC list, it was bigger due to the patch being in a series... This is truly the V3 of the patch, below is the diff between versions: V3: - added Evan's review tag - thanks! V2: - do not use spin_trylock anymore, to avoid messing with non-panic paths; now we just check the spinlock state in the panic notifier before taking it. Thanks Evan for the review! [0] https://lore.kernel.org/lkml/20220719195325.402745-4-gpiccoli@igalia.com/ drivers/firmware/google/gsmi.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/drivers/firmware/google/gsmi.c b/drivers/firmware/google/gsmi.c index adaa492c3d2d..3ef5f3c0b4e4 100644 --- a/drivers/firmware/google/gsmi.c +++ b/drivers/firmware/google/gsmi.c @@ -681,6 +681,14 @@ static struct notifier_block gsmi_die_notifier = { static int gsmi_panic_callback(struct notifier_block *nb, unsigned long reason, void *arg) { + /* + * Perform the lock check before effectively trying + * to acquire it on gsmi_shutdown_reason() to avoid + * potential lockups in atomic context. + */ + if (spin_is_locked(&gsmi_dev.lock)) + return NOTIFY_DONE; + gsmi_shutdown_reason(GSMI_SHUTDOWN_PANIC); return NOTIFY_DONE; }