From patchwork Fri Mar 1 03:12:01 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Jann Horn X-Patchwork-Id: 10834393 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 008CA17E9 for ; Fri, 1 Mar 2019 03:12:37 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id DFA9C2F9D4 for ; Fri, 1 Mar 2019 03:12:36 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id D3EDB2FBC4; Fri, 1 Mar 2019 03:12:36 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-15.5 required=2.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,RCVD_IN_DNSWL_HI, USER_IN_DEF_DKIM_WL autolearn=ham version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 6E9D02F9D4 for ; Fri, 1 Mar 2019 03:12:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731073AbfCADMc (ORCPT ); Thu, 28 Feb 2019 22:12:32 -0500 Received: from mail-oi1-f201.google.com ([209.85.167.201]:46530 "EHLO mail-oi1-f201.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728026AbfCADMc (ORCPT ); Thu, 28 Feb 2019 22:12:32 -0500 Received: by mail-oi1-f201.google.com with SMTP id v138so9984835oie.13 for ; Thu, 28 Feb 2019 19:12:31 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=date:in-reply-to:message-id:mime-version:references:subject:from:to :cc; bh=hMuz8j9XixUzcJvX0z8nUg4Sq1ac3+nfj2XuL+HY2V4=; b=TrUYSuHUCl3uKhVR7ZbV/Q4/CCSUVyNQGxrdl8+tmAvG8klNbrpqOdG5peMwcsduKt e0Q0WtF7CnULR6b9/93d+2iVnM+VarfcIirY+Jy7Mg/x0M368p3xQ9BHxC2cXYvrQCvv F/Tp9RNlxO/Dg6fbhAgZsL/U5JLGZxzpaY6xA+P5Hhlnl773EY/eZa2u/icRMfx61LDW mMq5iC+1AaWP+USSSnKlMCMe5sL7OBejJcTZlMPKjRKcSnwSycqOKLYqj5Xwg8l/H3D/ kwSVi6HUyXJkeCWraKOvA2PalGdsCy26pxDrFlJ7Mu0R8XoUUlfI6owX835rJKSEIK1B pvsQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:in-reply-to:message-id:mime-version :references:subject:from:to:cc; bh=hMuz8j9XixUzcJvX0z8nUg4Sq1ac3+nfj2XuL+HY2V4=; b=k4KEA09CQQ8PWI1iuqmuYBa7IXzLA39Yude1aIX0KoSGK4JgfjjFQY8XvjxN2Tydgz 3hf56Pwe6+IIsmBhdekfoFzVlV6valqs4twgI86CDsrszZtzW+sPJBE/1I4TbtIDog6W lEHIxFvyKpkPN5Fi0K+Bo9P4DMldyTR+hT5+WwjBmNryPEaEQF6l3y/uCqRZLIOaWUBA GyVDOOjuSYP9huCPiWORts09Cc3s4kABrWYZdjaw+kVZnUhCgHI4uZ5TCPEql06ZdzN3 xFG3AgtkSarDzXuenX20TQX7rP8orTz5+Jh6JMAbXtW8j4RR+9p2PfmMc6Kv3YTqP0qN luLw== X-Gm-Message-State: APjAAAWsnovWYa4+wYEoezpS3u/yuCc4QwOLwIWpoSG2DDvcr9Z+nStt FjWOI0knGMPmZuQ3J+ehuBDLLYexig== X-Google-Smtp-Source: APXvYqw6maUBSysTvwm6SV+PE/30VdvGuFkN36ozLAszM2/1+/oFumlBkxLFMBg5HdhLSqOzfwU2GVl6cQ== X-Received: by 2002:a05:6830:1205:: with SMTP id r5mr1740472otp.62.1551409951508; Thu, 28 Feb 2019 19:12:31 -0800 (PST) Date: Fri, 1 Mar 2019 04:12:01 +0100 In-Reply-To: <20190301031201.7416-1-jannh@google.com> Message-Id: <20190301031201.7416-2-jannh@google.com> Mime-Version: 1.0 References: <20190301031201.7416-1-jannh@google.com> X-Mailer: git-send-email 2.21.0.352.gf09ad66450-goog Subject: [PATCH 2/2] x86/unwind: add hardcoded ORC entry for NULL From: Jann Horn To: Thomas Gleixner , Ingo Molnar , Borislav Petkov , jannh@google.com Cc: Andrew Morton , Josh Poimboeuf , syzbot , "H. Peter Anvin" , x86@kernel.org, linux-kernel@vger.kernel.org, Masahiro Yamada , Michal Marek , linux-kbuild@vger.kernel.org Sender: linux-kbuild-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kbuild@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP When the ORC unwinder is invoked for an oops caused by IP==0, it currently has no idea what to do because there is no debug information for the stack frame of NULL. But if RIP is NULL, it is very likely that the last successfully executed instruction was an indirect CALL/JMP, and it is possible to unwind out in the same way as for the first instruction of a normal function. Hardcode a corresponding ORC entry. With an artificially-added NULL call in prctl_set_seccomp(), before this patch, the trace is: Call Trace: ? __x64_sys_prctl+0x402/0x680 ? __ia32_sys_prctl+0x6e0/0x6e0 ? __do_page_fault+0x457/0x620 ? do_syscall_64+0x6d/0x160 ? entry_SYSCALL_64_after_hwframe+0x44/0xa9 After this patch, the trace looks like this: Call Trace: __x64_sys_prctl+0x402/0x680 ? __ia32_sys_prctl+0x6e0/0x6e0 ? __do_page_fault+0x457/0x620 do_syscall_64+0x6d/0x160 entry_SYSCALL_64_after_hwframe+0x44/0xa9 prctl_set_seccomp() still doesn't show up in the trace because for some reason, tail call optimization is only disabled in builds that use the frame pointer unwinder. Signed-off-by: Jann Horn Acked-by: Josh Poimboeuf --- Is there a reason why the top-level Makefile only sets -fno-optimize-sibling-calls if CONFIG_FRAME_POINTER is set? I suspect that this is just a historical thing, because reliable unwinding didn't work without frame pointers until ORC came along. I'm not quite sure how best to express "don't do tail optimization if either frame pointers are used or ORC is used" in a Makefile, and whether we want an indirection through Kconfig for that, so I'm not doing anything about it in this series. Can someone send a patch to deal with it properly? arch/x86/kernel/unwind_orc.c | 17 +++++++++++++++++ 1 file changed, 17 insertions(+) diff --git a/arch/x86/kernel/unwind_orc.c b/arch/x86/kernel/unwind_orc.c index 26038eacf74a..89be1be1790c 100644 --- a/arch/x86/kernel/unwind_orc.c +++ b/arch/x86/kernel/unwind_orc.c @@ -113,6 +113,20 @@ static struct orc_entry *orc_ftrace_find(unsigned long ip) } #endif +/* + * If we crash with IP==0, the last successfully executed instruction + * was probably an indirect function call with a NULL function pointer, + * and we don't have unwind information for NULL. + * This hardcoded ORC entry for IP==0 allows us to unwind from a NULL function + * pointer into its parent and then continue normally from there. + */ +static struct orc_entry null_orc_entry = { + .sp_offset = sizeof(long), + .sp_reg = ORC_REG_SP, + .bp_reg = ORC_REG_UNDEFINED, + .type = ORC_TYPE_CALL +}; + static struct orc_entry *orc_find(unsigned long ip) { static struct orc_entry *orc; @@ -120,6 +134,9 @@ static struct orc_entry *orc_find(unsigned long ip) if (!orc_init) return NULL; + if (ip == 0) + return &null_orc_entry; + /* For non-init vmlinux addresses, use the fast lookup table: */ if (ip >= LOOKUP_START_IP && ip < LOOKUP_STOP_IP) { unsigned int idx, start, stop;