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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2E7E8C433EF for ; Sun, 26 Jun 2022 08:21:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233974AbiFZIVa (ORCPT ); Sun, 26 Jun 2022 04:21:30 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53580 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232734AbiFZIVa (ORCPT ); Sun, 26 Jun 2022 04:21:30 -0400 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 26C1912AB3; Sun, 26 Jun 2022 01:21:29 -0700 (PDT) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 1C77DD6E; Sun, 26 Jun 2022 01:21:29 -0700 (PDT) Received: from FVFF77S0Q05N (unknown [10.57.71.61]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 14C293F792; Sun, 26 Jun 2022 01:21:26 -0700 (PDT) Date: Sun, 26 Jun 2022 09:21:23 +0100 From: Mark Rutland To: madvenka@linux.microsoft.com Cc: broonie@kernel.org, jpoimboe@redhat.com, ardb@kernel.org, nobuta.keiya@fujitsu.com, sjitindarsingh@gmail.com, catalin.marinas@arm.com, will@kernel.org, jamorris@linux.microsoft.com, linux-arm-kernel@lists.infradead.org, live-patching@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v15 3/6] arm64: Make the unwind loop in unwind() similar to other architectures Message-ID: References: <20220617210717.27126-1-madvenka@linux.microsoft.com> <20220617210717.27126-4-madvenka@linux.microsoft.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220617210717.27126-4-madvenka@linux.microsoft.com> Precedence: bulk List-ID: X-Mailing-List: live-patching@vger.kernel.org On Fri, Jun 17, 2022 at 04:07:14PM -0500, madvenka@linux.microsoft.com wrote: > From: "Madhavan T. Venkataraman" > > Change the loop in unwind() > =========================== > > Change the unwind loop in unwind() to: > > while (unwind_continue(state, consume_entry, cookie)) > unwind_next(state); > > This is easy to understand and maintain. > New function unwind_continue() > ============================== > > Define a new function unwind_continue() that is used in the unwind loop > to check for conditions that terminate a stack trace. > > The conditions checked are: > > - If the bottom of the stack (final frame) has been reached, > terminate. > > - If the consume_entry() function returns false, the caller of > unwind has asked to terminate the stack trace. So, terminate. > > - If unwind_next() failed for some reason (like stack corruption), > terminate. I'm a bit confused as to why this structure, since AFAICT this doesn't match other architectures (looking at x86, powerpc, and s390). I note that x86 has: * In arch_stack_walk(): for (unwind_start(&state, task, regs, NULL); !unwind_done(&state); unwind_next_frame(&state)) { ... if (!consume_entry(...)) break; ... } * In arch_stack_walk_reliable(): for (unwind_start(&state, task, NULL, NULL); !unwind_done(&state) && !unwind_error(&state); unwind_next_frame(&state)) { ... if (!consume_entry(...) return -EINVAL; } ... and back in v6 I suggeted exactly that shape: https://lore.kernel.org/linux-arm-kernel/20210728165635.GA47345@C02TD0UTHF1T.local/ > > Do not return an error value from unwind_next() > =============================================== > > We want to check for terminating conditions only in unwind_continue() from > the unwinder loop. So, do not return an error value from unwind_next(). > Simply set a flag in unwind_state and check the flag in unwind_continue(). I'm fine with the concept of moving ghe return value out of unwind_next() (e.g. if we go with an x86-like structure), but I don't think that we should centralize the other checks *and* the consumption within unwind_continue(), as I think those are two separate things. > > Final FP > ======== > > Introduce a new field "final_fp" in "struct unwind_state". Initialize this > to the final frame of the stack trace: > > task_pt_regs(task)->stackframe > > This is where the stacktrace must terminate if it is successful. Add an > explicit comment to that effect. Can we please make this change as a preparatory step, as with the 'task' field? We can wrap this in a helper like: static bool is_final_frame(struct unwind state *state) { return state->fp == state->final_fp; } ... and use that in the main loop. Thanks, Mark. > > Signed-off-by: Madhavan T. Venkataraman > Reviewed-by: Mark Brown > --- > arch/arm64/kernel/stacktrace.c | 78 ++++++++++++++++++++++------------ > 1 file changed, 52 insertions(+), 26 deletions(-) > > diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c > index 8e43444d50e2..c749129aba5a 100644 > --- a/arch/arm64/kernel/stacktrace.c > +++ b/arch/arm64/kernel/stacktrace.c > @@ -40,6 +40,10 @@ > * value. > * > * @task: The task being unwound. > + * > + * @final_fp: Pointer to the final frame. > + * > + * @failed: Unwind failed. > */ > struct unwind_state { > unsigned long fp; > @@ -51,6 +55,8 @@ struct unwind_state { > struct llist_node *kr_cur; > #endif > struct task_struct *task; > + unsigned long final_fp; > + bool failed; > }; > > static void unwind_init_common(struct unwind_state *state, > @@ -73,6 +79,10 @@ static void unwind_init_common(struct unwind_state *state, > bitmap_zero(state->stacks_done, __NR_STACK_TYPES); > state->prev_fp = 0; > state->prev_type = STACK_TYPE_UNKNOWN; > + state->failed = false; > + > + /* Stack trace terminates here. */ > + state->final_fp = (unsigned long)task_pt_regs(task)->stackframe; > } > > /* > @@ -126,6 +136,25 @@ static inline void unwind_init_from_task(struct unwind_state *state, > state->pc = thread_saved_pc(task); > } > > +static bool notrace unwind_continue(struct unwind_state *state, > + stack_trace_consume_fn consume_entry, > + void *cookie) > +{ > + if (state->failed) { > + /* PC is suspect. Cannot consume it. */ > + return false; > + } > + > + if (!consume_entry(cookie, state->pc)) { > + /* Caller terminated the unwind. */ > + state->failed = true; > + return false; > + } > + > + return state->fp != state->final_fp; > +} > +NOKPROBE_SYMBOL(unwind_continue); > + > /* > * Unwind from one frame record (A) to the next frame record (B). > * > @@ -133,24 +162,26 @@ static inline void unwind_init_from_task(struct unwind_state *state, > * records (e.g. a cycle), determined based on the location and fp value of A > * and the location (but not the fp value) of B. > */ > -static int notrace unwind_next(struct unwind_state *state) > +static void notrace unwind_next(struct unwind_state *state) > { > struct task_struct *tsk = state->task; > unsigned long fp = state->fp; > struct stack_info info; > > - /* Final frame; nothing to unwind */ > - if (fp == (unsigned long)task_pt_regs(tsk)->stackframe) > - return -ENOENT; > - > - if (fp & 0x7) > - return -EINVAL; > + if (fp & 0x7) { > + state->failed = true; > + return; > + } > > - if (!on_accessible_stack(tsk, fp, 16, &info)) > - return -EINVAL; > + if (!on_accessible_stack(tsk, fp, 16, &info)) { > + state->failed = true; > + return; > + } > > - if (test_bit(info.type, state->stacks_done)) > - return -EINVAL; > + if (test_bit(info.type, state->stacks_done)) { > + state->failed = true; > + return; > + } > > /* > * As stacks grow downward, any valid record on the same stack must be > @@ -166,8 +197,10 @@ static int notrace unwind_next(struct unwind_state *state) > * stack. > */ > if (info.type == state->prev_type) { > - if (fp <= state->prev_fp) > - return -EINVAL; > + if (fp <= state->prev_fp) { > + state->failed = true; > + return; > + } > } else { > set_bit(state->prev_type, state->stacks_done); > } > @@ -195,8 +228,10 @@ static int notrace unwind_next(struct unwind_state *state) > */ > orig_pc = ftrace_graph_ret_addr(tsk, NULL, state->pc, > (void *)state->fp); > - if (WARN_ON_ONCE(state->pc == orig_pc)) > - return -EINVAL; > + if (WARN_ON_ONCE(state->pc == orig_pc)) { > + state->failed = true; > + return; > + } > state->pc = orig_pc; > } > #endif /* CONFIG_FUNCTION_GRAPH_TRACER */ > @@ -204,23 +239,14 @@ static int notrace unwind_next(struct unwind_state *state) > if (is_kretprobe_trampoline(state->pc)) > state->pc = kretprobe_find_ret_addr(tsk, (void *)state->fp, &state->kr_cur); > #endif > - > - return 0; > } > NOKPROBE_SYMBOL(unwind_next); > > static void notrace unwind(struct unwind_state *state, > stack_trace_consume_fn consume_entry, void *cookie) > { > - while (1) { > - int ret; > - > - if (!consume_entry(cookie, state->pc)) > - break; > - ret = unwind_next(state); > - if (ret < 0) > - break; > - } > + while (unwind_continue(state, consume_entry, cookie)) > + unwind_next(state); > } > NOKPROBE_SYMBOL(unwind); > > -- > 2.25.1 > 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 E4687C433EF for ; Sun, 26 Jun 2022 08:22:40 +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=Z8W4qsVS6Ti8cR7G7bffQ3mw5UUmXHTsFcVbebPQ0x8=; b=oSA9dWwWEiKFlx BId0JYRefp9mC5pnCFv6He+voc+FVZKMYNoZY1Dk/xuCS74GFMdswdgzd+jBWGqN40oW0RfldAKVZ g6LahfKvoKmhABQxIFVxVAOPdkkyHRbInh/pSmVmy0MSemTZWKKJOsIHngB7dyl2+puv3FT33Z/aM gvy962Y+P+rxxI4bit4GuNTsbmiEWnNxHg4sPMNoUcOU1LWaXIgrk7827wPFVaIkGk6VmmdivaZ7O kqrHDBgJ/USmfB5gK2MvnF9Ro/dvv+B8PygNRnlz4GNzRXUIZkCoBYbeT3DBPzN4MeivdVgrwb8CQ u6sIJENoD9WN1gwi0aWA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1o5NWS-00Aatk-77; Sun, 26 Jun 2022 08:21:36 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1o5NWO-00Aas9-6F for linux-arm-kernel@lists.infradead.org; Sun, 26 Jun 2022 08:21:34 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 1C77DD6E; Sun, 26 Jun 2022 01:21:29 -0700 (PDT) Received: from FVFF77S0Q05N (unknown [10.57.71.61]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 14C293F792; Sun, 26 Jun 2022 01:21:26 -0700 (PDT) Date: Sun, 26 Jun 2022 09:21:23 +0100 From: Mark Rutland To: madvenka@linux.microsoft.com Cc: broonie@kernel.org, jpoimboe@redhat.com, ardb@kernel.org, nobuta.keiya@fujitsu.com, sjitindarsingh@gmail.com, catalin.marinas@arm.com, will@kernel.org, jamorris@linux.microsoft.com, linux-arm-kernel@lists.infradead.org, live-patching@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v15 3/6] arm64: Make the unwind loop in unwind() similar to other architectures Message-ID: References: <20220617210717.27126-1-madvenka@linux.microsoft.com> <20220617210717.27126-4-madvenka@linux.microsoft.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20220617210717.27126-4-madvenka@linux.microsoft.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20220626_012132_371967_D19D75F1 X-CRM114-Status: GOOD ( 37.76 ) 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 Fri, Jun 17, 2022 at 04:07:14PM -0500, madvenka@linux.microsoft.com wrote: > From: "Madhavan T. Venkataraman" > > Change the loop in unwind() > =========================== > > Change the unwind loop in unwind() to: > > while (unwind_continue(state, consume_entry, cookie)) > unwind_next(state); > > This is easy to understand and maintain. > New function unwind_continue() > ============================== > > Define a new function unwind_continue() that is used in the unwind loop > to check for conditions that terminate a stack trace. > > The conditions checked are: > > - If the bottom of the stack (final frame) has been reached, > terminate. > > - If the consume_entry() function returns false, the caller of > unwind has asked to terminate the stack trace. So, terminate. > > - If unwind_next() failed for some reason (like stack corruption), > terminate. I'm a bit confused as to why this structure, since AFAICT this doesn't match other architectures (looking at x86, powerpc, and s390). I note that x86 has: * In arch_stack_walk(): for (unwind_start(&state, task, regs, NULL); !unwind_done(&state); unwind_next_frame(&state)) { ... if (!consume_entry(...)) break; ... } * In arch_stack_walk_reliable(): for (unwind_start(&state, task, NULL, NULL); !unwind_done(&state) && !unwind_error(&state); unwind_next_frame(&state)) { ... if (!consume_entry(...) return -EINVAL; } ... and back in v6 I suggeted exactly that shape: https://lore.kernel.org/linux-arm-kernel/20210728165635.GA47345@C02TD0UTHF1T.local/ > > Do not return an error value from unwind_next() > =============================================== > > We want to check for terminating conditions only in unwind_continue() from > the unwinder loop. So, do not return an error value from unwind_next(). > Simply set a flag in unwind_state and check the flag in unwind_continue(). I'm fine with the concept of moving ghe return value out of unwind_next() (e.g. if we go with an x86-like structure), but I don't think that we should centralize the other checks *and* the consumption within unwind_continue(), as I think those are two separate things. > > Final FP > ======== > > Introduce a new field "final_fp" in "struct unwind_state". Initialize this > to the final frame of the stack trace: > > task_pt_regs(task)->stackframe > > This is where the stacktrace must terminate if it is successful. Add an > explicit comment to that effect. Can we please make this change as a preparatory step, as with the 'task' field? We can wrap this in a helper like: static bool is_final_frame(struct unwind state *state) { return state->fp == state->final_fp; } ... and use that in the main loop. Thanks, Mark. > > Signed-off-by: Madhavan T. Venkataraman > Reviewed-by: Mark Brown > --- > arch/arm64/kernel/stacktrace.c | 78 ++++++++++++++++++++++------------ > 1 file changed, 52 insertions(+), 26 deletions(-) > > diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c > index 8e43444d50e2..c749129aba5a 100644 > --- a/arch/arm64/kernel/stacktrace.c > +++ b/arch/arm64/kernel/stacktrace.c > @@ -40,6 +40,10 @@ > * value. > * > * @task: The task being unwound. > + * > + * @final_fp: Pointer to the final frame. > + * > + * @failed: Unwind failed. > */ > struct unwind_state { > unsigned long fp; > @@ -51,6 +55,8 @@ struct unwind_state { > struct llist_node *kr_cur; > #endif > struct task_struct *task; > + unsigned long final_fp; > + bool failed; > }; > > static void unwind_init_common(struct unwind_state *state, > @@ -73,6 +79,10 @@ static void unwind_init_common(struct unwind_state *state, > bitmap_zero(state->stacks_done, __NR_STACK_TYPES); > state->prev_fp = 0; > state->prev_type = STACK_TYPE_UNKNOWN; > + state->failed = false; > + > + /* Stack trace terminates here. */ > + state->final_fp = (unsigned long)task_pt_regs(task)->stackframe; > } > > /* > @@ -126,6 +136,25 @@ static inline void unwind_init_from_task(struct unwind_state *state, > state->pc = thread_saved_pc(task); > } > > +static bool notrace unwind_continue(struct unwind_state *state, > + stack_trace_consume_fn consume_entry, > + void *cookie) > +{ > + if (state->failed) { > + /* PC is suspect. Cannot consume it. */ > + return false; > + } > + > + if (!consume_entry(cookie, state->pc)) { > + /* Caller terminated the unwind. */ > + state->failed = true; > + return false; > + } > + > + return state->fp != state->final_fp; > +} > +NOKPROBE_SYMBOL(unwind_continue); > + > /* > * Unwind from one frame record (A) to the next frame record (B). > * > @@ -133,24 +162,26 @@ static inline void unwind_init_from_task(struct unwind_state *state, > * records (e.g. a cycle), determined based on the location and fp value of A > * and the location (but not the fp value) of B. > */ > -static int notrace unwind_next(struct unwind_state *state) > +static void notrace unwind_next(struct unwind_state *state) > { > struct task_struct *tsk = state->task; > unsigned long fp = state->fp; > struct stack_info info; > > - /* Final frame; nothing to unwind */ > - if (fp == (unsigned long)task_pt_regs(tsk)->stackframe) > - return -ENOENT; > - > - if (fp & 0x7) > - return -EINVAL; > + if (fp & 0x7) { > + state->failed = true; > + return; > + } > > - if (!on_accessible_stack(tsk, fp, 16, &info)) > - return -EINVAL; > + if (!on_accessible_stack(tsk, fp, 16, &info)) { > + state->failed = true; > + return; > + } > > - if (test_bit(info.type, state->stacks_done)) > - return -EINVAL; > + if (test_bit(info.type, state->stacks_done)) { > + state->failed = true; > + return; > + } > > /* > * As stacks grow downward, any valid record on the same stack must be > @@ -166,8 +197,10 @@ static int notrace unwind_next(struct unwind_state *state) > * stack. > */ > if (info.type == state->prev_type) { > - if (fp <= state->prev_fp) > - return -EINVAL; > + if (fp <= state->prev_fp) { > + state->failed = true; > + return; > + } > } else { > set_bit(state->prev_type, state->stacks_done); > } > @@ -195,8 +228,10 @@ static int notrace unwind_next(struct unwind_state *state) > */ > orig_pc = ftrace_graph_ret_addr(tsk, NULL, state->pc, > (void *)state->fp); > - if (WARN_ON_ONCE(state->pc == orig_pc)) > - return -EINVAL; > + if (WARN_ON_ONCE(state->pc == orig_pc)) { > + state->failed = true; > + return; > + } > state->pc = orig_pc; > } > #endif /* CONFIG_FUNCTION_GRAPH_TRACER */ > @@ -204,23 +239,14 @@ static int notrace unwind_next(struct unwind_state *state) > if (is_kretprobe_trampoline(state->pc)) > state->pc = kretprobe_find_ret_addr(tsk, (void *)state->fp, &state->kr_cur); > #endif > - > - return 0; > } > NOKPROBE_SYMBOL(unwind_next); > > static void notrace unwind(struct unwind_state *state, > stack_trace_consume_fn consume_entry, void *cookie) > { > - while (1) { > - int ret; > - > - if (!consume_entry(cookie, state->pc)) > - break; > - ret = unwind_next(state); > - if (ret < 0) > - break; > - } > + while (unwind_continue(state, consume_entry, cookie)) > + unwind_next(state); > } > NOKPROBE_SYMBOL(unwind); > > -- > 2.25.1 > _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel