From: "Madhavan T. Venkataraman" <madvenka@linux.microsoft.com> To: Mark Brown <broonie@kernel.org> Cc: mark.rutland@arm.com, jpoimboe@redhat.com, ardb@kernel.org, nobuta.keiya@fujitsu.com, sjitindarsingh@gmail.com, catalin.marinas@arm.com, will@kernel.org, jmorris@namei.org, linux-arm-kernel@lists.infradead.org, live-patching@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v11 4/5] arm64: Introduce stack trace reliability checks in the unwinder Date: Thu, 25 Nov 2021 10:59:27 -0600 [thread overview] Message-ID: <704d73f6-30e2-08e0-3a5c-d3639d8b2da1@linux.microsoft.com> (raw) In-Reply-To: <YZ+kLPT+h6ZGw20p@sirena.org.uk> On 11/25/21 8:56 AM, Mark Brown wrote: > On Tue, Nov 23, 2021 at 01:37:22PM -0600, madvenka@linux.microsoft.com wrote: > >> Introduce arch_stack_walk_reliable() for ARM64. This works like >> arch_stack_walk() except that it returns -EINVAL if the stack trace is not >> reliable. > >> Until all the reliability checks are in place, arch_stack_walk_reliable() >> may not be used by livepatch. But it may be used by debug and test code. > > Probably also worth noting that this doesn't select > HAVE_RELIABLE_STACKTRACE which is what any actual users are going to use > to identify if the architecture has the feature. I would have been > tempted to add arch_stack_walk() as a separate patch but equally having > the user code there (even if it itself can't yet be used...) helps with > reviewing the actual unwinder so I don't mind. > I did not select HAVE_RELIABLE_STACKTRACE just in case we think that some more reliability checks need to be added. But if reviewers agree that this patch series contains all the reliability checks we need, I will add a patch to select HAVE_RELIABLE_STACKTRACE to the series. >> +static void unwind_check_reliability(struct task_struct *task, >> + struct stackframe *frame) >> +{ >> + if (frame->fp == (unsigned long)task_pt_regs(task)->stackframe) { >> + /* Final frame; no more unwind, no need to check reliability */ >> + return; >> + } > > If the unwinder carries on for some reason (the code for that is > elsewhere and may be updated separately...) then this will start > checking again. I'm not sure if this is a *problem* as such but the > thing about this being the final frame coupled with not actually > explicitly stopping the unwind here makes me think this should at least > be clearer, the comment begs the question about what happens if > something decides it is not in fact the final frame. > I can address this by adding an explicit comment to that effect. For example, define a separate function to check for the final frame: /* * Check if this is the final frame. Unwind must stop at the final * frame. */ static inline bool unwind_is_final_frame(struct task_struct *task, struct stackframe *frame) { return frame->fp == (unsigned long)task_pt_regs(task)->stackframe; } Then, use this function in unwind_check_reliability() and unwind_continue(). Is this acceptable? Madhavan
WARNING: multiple messages have this Message-ID (diff)
From: "Madhavan T. Venkataraman" <madvenka@linux.microsoft.com> To: Mark Brown <broonie@kernel.org> Cc: mark.rutland@arm.com, jpoimboe@redhat.com, ardb@kernel.org, nobuta.keiya@fujitsu.com, sjitindarsingh@gmail.com, catalin.marinas@arm.com, will@kernel.org, jmorris@namei.org, linux-arm-kernel@lists.infradead.org, live-patching@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v11 4/5] arm64: Introduce stack trace reliability checks in the unwinder Date: Thu, 25 Nov 2021 10:59:27 -0600 [thread overview] Message-ID: <704d73f6-30e2-08e0-3a5c-d3639d8b2da1@linux.microsoft.com> (raw) In-Reply-To: <YZ+kLPT+h6ZGw20p@sirena.org.uk> On 11/25/21 8:56 AM, Mark Brown wrote: > On Tue, Nov 23, 2021 at 01:37:22PM -0600, madvenka@linux.microsoft.com wrote: > >> Introduce arch_stack_walk_reliable() for ARM64. This works like >> arch_stack_walk() except that it returns -EINVAL if the stack trace is not >> reliable. > >> Until all the reliability checks are in place, arch_stack_walk_reliable() >> may not be used by livepatch. But it may be used by debug and test code. > > Probably also worth noting that this doesn't select > HAVE_RELIABLE_STACKTRACE which is what any actual users are going to use > to identify if the architecture has the feature. I would have been > tempted to add arch_stack_walk() as a separate patch but equally having > the user code there (even if it itself can't yet be used...) helps with > reviewing the actual unwinder so I don't mind. > I did not select HAVE_RELIABLE_STACKTRACE just in case we think that some more reliability checks need to be added. But if reviewers agree that this patch series contains all the reliability checks we need, I will add a patch to select HAVE_RELIABLE_STACKTRACE to the series. >> +static void unwind_check_reliability(struct task_struct *task, >> + struct stackframe *frame) >> +{ >> + if (frame->fp == (unsigned long)task_pt_regs(task)->stackframe) { >> + /* Final frame; no more unwind, no need to check reliability */ >> + return; >> + } > > If the unwinder carries on for some reason (the code for that is > elsewhere and may be updated separately...) then this will start > checking again. I'm not sure if this is a *problem* as such but the > thing about this being the final frame coupled with not actually > explicitly stopping the unwind here makes me think this should at least > be clearer, the comment begs the question about what happens if > something decides it is not in fact the final frame. > I can address this by adding an explicit comment to that effect. For example, define a separate function to check for the final frame: /* * Check if this is the final frame. Unwind must stop at the final * frame. */ static inline bool unwind_is_final_frame(struct task_struct *task, struct stackframe *frame) { return frame->fp == (unsigned long)task_pt_regs(task)->stackframe; } Then, use this function in unwind_check_reliability() and unwind_continue(). Is this acceptable? Madhavan _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2021-11-25 17:01 UTC|newest] Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top [not found] <8b861784d85a21a9bf08598938c11aff1b1249b9> 2021-11-23 19:37 ` [PATCH v11 0/5] arm64: Reorganize the unwinder and implement stack trace reliability checks madvenka 2021-11-23 19:37 ` madvenka 2021-11-23 19:37 ` [PATCH v11 1/5] arm64: Call stack_backtrace() only from within walk_stackframe() madvenka 2021-11-23 19:37 ` madvenka 2021-11-25 13:48 ` Mark Brown 2021-11-25 13:48 ` Mark Brown 2021-11-30 15:05 ` Mark Rutland 2021-11-30 15:05 ` Mark Rutland 2021-11-30 17:13 ` Madhavan T. Venkataraman 2021-11-30 17:13 ` Madhavan T. Venkataraman 2021-11-30 18:29 ` Mark Rutland 2021-11-30 18:29 ` Mark Rutland 2021-11-30 20:29 ` Madhavan T. Venkataraman 2021-11-30 20:29 ` Madhavan T. Venkataraman 2021-12-10 4:13 ` Madhavan T. Venkataraman 2021-12-10 4:13 ` Madhavan T. Venkataraman 2021-11-23 19:37 ` [PATCH v11 2/5] arm64: Rename unwinder functions madvenka 2021-11-23 19:37 ` madvenka 2021-11-24 17:10 ` Mark Brown 2021-11-24 17:10 ` Mark Brown 2021-11-30 15:08 ` Mark Rutland 2021-11-30 15:08 ` Mark Rutland 2021-11-30 17:15 ` Madhavan T. Venkataraman 2021-11-30 17:15 ` Madhavan T. Venkataraman 2021-11-23 19:37 ` [PATCH v11 3/5] arm64: Make the unwind loop in unwind() similar to other architectures madvenka 2021-11-23 19:37 ` madvenka 2021-11-25 14:30 ` Mark Brown 2021-11-25 14:30 ` Mark Brown 2021-11-23 19:37 ` [PATCH v11 4/5] arm64: Introduce stack trace reliability checks in the unwinder madvenka 2021-11-23 19:37 ` madvenka 2021-11-25 14:56 ` Mark Brown 2021-11-25 14:56 ` Mark Brown 2021-11-25 16:59 ` Madhavan T. Venkataraman [this message] 2021-11-25 16:59 ` Madhavan T. Venkataraman 2021-11-26 13:29 ` Mark Brown 2021-11-26 13:29 ` Mark Brown 2021-11-26 17:23 ` Madhavan T. Venkataraman 2021-11-26 17:23 ` Madhavan T. Venkataraman 2021-11-23 19:37 ` [PATCH v11 5/5] arm64: Create a list of SYM_CODE functions, check return PC against list madvenka 2021-11-23 19:37 ` madvenka 2021-11-25 15:05 ` Mark Brown 2021-11-25 15:05 ` Mark Brown
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