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 X-Spam-Level: X-Spam-Status: No, score=-8.3 required=3.0 tests=DKIM_ADSP_CUSTOM_MED, DKIM_INVALID,DKIM_SIGNED,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_PASS,URIBL_BLOCKED,USER_AGENT_MUTT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 73410C282D8 for ; Sat, 2 Feb 2019 01:16:43 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 964A12148D for ; Sat, 2 Feb 2019 01:16:42 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="vRw2twCK" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 964A12148D Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=gmail.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from lists.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 43rwzX0YM1zDqjh for ; Sat, 2 Feb 2019 12:16:40 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; spf=pass (mailfrom) smtp.mailfrom=gmail.com (client-ip=2607:f8b0:4864:20::641; helo=mail-pl1-x641.google.com; envelope-from=bsingharora@gmail.com; receiver=) Authentication-Results: lists.ozlabs.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: lists.ozlabs.org; dkim=pass (2048-bit key; unprotected) header.d=gmail.com header.i=@gmail.com header.b="vRw2twCK"; dkim-atps=neutral Received: from mail-pl1-x641.google.com (mail-pl1-x641.google.com [IPv6:2607:f8b0:4864:20::641]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 43rwxd0Jn4zDqhl for ; Sat, 2 Feb 2019 12:15:00 +1100 (AEDT) Received: by mail-pl1-x641.google.com with SMTP id p4so800077plq.11 for ; Fri, 01 Feb 2019 17:15:00 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=0rJ7i+EV9cWj3/MnMr0WxrLS3AGD0khiA71WozRXWsY=; b=vRw2twCK5YipJ78jZe0ia/FV8SD3jMr5UhhJhGGlpQoFdw96oU0oqN0LWlRG0GUC5d Q4LNWZNC9xaaINWO+c+nzNBXNimHpDIyTcwkVH5GcnGrKZ7U2GPKLcmNVJmw1rZq2NGX SqiPhmqOdMc7DN4qOmzs9VqpIaHNE56Y4C0XVpvYq4FO2AeLEMh2FczE7vIV6b54nITx frzzI0/sGb704XNnvElYr4Oqx1lOGm+GINKoEdu3WSGz9i2WyBpGGZWfx6bWY2tQb/7Z +gpVBtM2LXtlF6rxIE3BCg7Nek4myBsRU67ZSIKc0WkgYf9tsOIAsrXIkmSwz7q3RL1F Zn3A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=0rJ7i+EV9cWj3/MnMr0WxrLS3AGD0khiA71WozRXWsY=; b=gmOfP4UOjjpsWyUJTCyJHEBgD6TVFXYnOeJE1TGhSMCWBJM3/IEyvZvn8wlMitA20N PoKCe5T5bJ5EYBwN8XavjIwNDq9OIlh6UzAmaAqzXlLyqGXxUv5dLLXJqYHIHFUO4eJx WVA9Y0pj580M1zgWgjDu/+4agbGMasz8PXYnbV2Oy2nM++NkUu0q91rxEW9qfLe4/z10 NrZ6SK21CxurXQrB5/6zcAEnIAToJqhqxi8WcD2/5tIymUWLabbkr5zoQ1NkBEJ3A373 lPGq2KlxqQi8l6P5yuOQTxGZxyFZUDHZ3i92KjZFvJxKmjuQaEjSC5D2KvoV254f0Aw1 kXHA== X-Gm-Message-State: AJcUukdSpGS+Gpu1J453cuDUAbDMGhI7AW8NqrSNNfSQUxXtZ+ZkmK0S cx7LINk67SCz05dDi5s2FlXUq4JJgUw= X-Google-Smtp-Source: ALg8bN5+FKSDjPtgEULcwzNRN+QiRcaez12HT1ekKJfTmviGjzipybskvQzISvLOFcYjQeVfj5WM9A== X-Received: by 2002:a17:902:2468:: with SMTP id m37mr42002179plg.314.1549070098955; Fri, 01 Feb 2019 17:14:58 -0800 (PST) Received: from localhost (14-202-194-140.static.tpgi.com.au. [14.202.194.140]) by smtp.gmail.com with ESMTPSA id z9sm27419422pfd.99.2019.02.01.17.14.57 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Fri, 01 Feb 2019 17:14:58 -0800 (PST) Date: Sat, 2 Feb 2019 12:14:55 +1100 From: Balbir Singh To: Joe Lawrence Subject: Re: [PATCH 1/4] powerpc/64s: Clear on-stack exception marker upon exception return Message-ID: <20190202011455.GN26056@350D> References: <20190122155724.27557-1-joe.lawrence@redhat.com> <20190122155724.27557-2-joe.lawrence@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190122155724.27557-2-joe.lawrence@redhat.com> User-Agent: Mutt/1.9.4 (2018-02-28) X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Nicolai Stange , Jiri Kosina , linux-kernel@vger.kernel.org, Torsten Duwe , Josh Poimboeuf , live-patching@vger.kernel.org, linuxppc-dev@lists.ozlabs.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Tue, Jan 22, 2019 at 10:57:21AM -0500, Joe Lawrence wrote: > From: Nicolai Stange > > The ppc64 specific implementation of the reliable stacktracer, > save_stack_trace_tsk_reliable(), bails out and reports an "unreliable > trace" whenever it finds an exception frame on the stack. Stack frames > are classified as exception frames if the STACK_FRAME_REGS_MARKER magic, > as written by exception prologues, is found at a particular location. > > However, as observed by Joe Lawrence, it is possible in practice that > non-exception stack frames can alias with prior exception frames and thus, > that the reliable stacktracer can find a stale STACK_FRAME_REGS_MARKER on > the stack. It in turn falsely reports an unreliable stacktrace and blocks > any live patching transition to finish. Said condition lasts until the > stack frame is overwritten/initialized by function call or other means. > > In principle, we could mitigate this by making the exception frame > classification condition in save_stack_trace_tsk_reliable() stronger: > in addition to testing for STACK_FRAME_REGS_MARKER, we could also take into > account that for all exceptions executing on the kernel stack > - their stack frames's backlink pointers always match what is saved > in their pt_regs instance's ->gpr[1] slot and that > - their exception frame size equals STACK_INT_FRAME_SIZE, a value > uncommonly large for non-exception frames. > > However, while these are currently true, relying on them would make the > reliable stacktrace implementation more sensitive towards future changes in > the exception entry code. Note that false negatives, i.e. not detecting > exception frames, would silently break the live patching consistency model. > > Furthermore, certain other places (diagnostic stacktraces, perf, xmon) > rely on STACK_FRAME_REGS_MARKER as well. > > Make the exception exit code clear the on-stack STACK_FRAME_REGS_MARKER > for those exceptions running on the "normal" kernel stack and returning > to kernelspace: because the topmost frame is ignored by the reliable stack > tracer anyway, returns to userspace don't need to take care of clearing > the marker. > > Furthermore, as I don't have the ability to test this on Book 3E or > 32 bits, limit the change to Book 3S and 64 bits. > > Finally, make the HAVE_RELIABLE_STACKTRACE Kconfig option depend on > PPC_BOOK3S_64 for documentation purposes. Before this patch, it depended > on PPC64 && CPU_LITTLE_ENDIAN and because CPU_LITTLE_ENDIAN implies > PPC_BOOK3S_64, there's no functional change here. > > Fixes: df78d3f61480 ("powerpc/livepatch: Implement reliable stack tracing for the consistency model") > Reported-by: Joe Lawrence > Signed-off-by: Nicolai Stange > Signed-off-by: Joe Lawrence > --- > arch/powerpc/Kconfig | 2 +- > arch/powerpc/kernel/entry_64.S | 7 +++++++ > 2 files changed, 8 insertions(+), 1 deletion(-) > > diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig > index 2890d36eb531..73bf87b1d274 100644 > --- a/arch/powerpc/Kconfig > +++ b/arch/powerpc/Kconfig > @@ -220,7 +220,7 @@ config PPC > select HAVE_PERF_USER_STACK_DUMP > select HAVE_RCU_TABLE_FREE if SMP > select HAVE_REGS_AND_STACK_ACCESS_API > - select HAVE_RELIABLE_STACKTRACE if PPC64 && CPU_LITTLE_ENDIAN > + select HAVE_RELIABLE_STACKTRACE if PPC_BOOK3S_64 && CPU_LITTLE_ENDIAN > select HAVE_SYSCALL_TRACEPOINTS > select HAVE_VIRT_CPU_ACCOUNTING > select HAVE_IRQ_TIME_ACCOUNTING > diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S > index 435927f549c4..a2c168b395d2 100644 > --- a/arch/powerpc/kernel/entry_64.S > +++ b/arch/powerpc/kernel/entry_64.S > @@ -1002,6 +1002,13 @@ END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR) > ld r2,_NIP(r1) > mtspr SPRN_SRR0,r2 > > + /* > + * Leaving a stale exception_marker on the stack can confuse > + * the reliable stack unwinder later on. Clear it. > + */ > + li r2,0 > + std r2,STACK_FRAME_OVERHEAD-16(r1) > + Could you please double check, r4 is already 0 at this point IIUC. So the change might be a simple std r4,STACK_FRAME_OVERHEAD-16(r1) Balbir