From: Masami Hiramatsu <mhiramat@kernel.org> To: Mark Rutland <mark.rutland@arm.com> Cc: Steven Rostedt <rostedt@goodmis.org>, "Naveen N . Rao" <naveen.n.rao@linux.vnet.ibm.com>, Ananth N Mavinakayanahalli <ananth@linux.ibm.com>, Ingo Molnar <mingo@kernel.org>, linux-kernel@vger.kernel.org, Sven Schnelle <svens@linux.ibm.com>, Catalin Marinas <catalin.marinas@arm.com>, Will Deacon <will@kernel.org>, Russell King <linux@armlinux.org.uk>, Nathan Chancellor <nathan@kernel.org>, Nick Desaulniers <ndesaulniers@google.com>, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH 3/8] arm64: kprobes: Record frame pointer with kretprobe instance Date: Thu, 14 Oct 2021 22:50:39 +0900 [thread overview] Message-ID: <20211014225039.b96ff7b7fa86f340ceb50192@kernel.org> (raw) In-Reply-To: <20211014102702.GB13770@C02TD0UTHF1T.local> On Thu, 14 Oct 2021 11:27:02 +0100 Mark Rutland <mark.rutland@arm.com> wrote: > On Thu, Oct 14, 2021 at 07:01:55PM +0900, Masami Hiramatsu wrote: > > On Thu, 14 Oct 2021 10:13:32 +0100 > > Mark Rutland <mark.rutland@arm.com> wrote: > > > > > On Thu, Oct 14, 2021 at 05:04:05PM +0900, Masami Hiramatsu wrote: > > > > On Wed, 13 Oct 2021 11:01:39 +0100 > > > > Mark Rutland <mark.rutland@arm.com> wrote: > > > > > > > > > On Fri, Oct 08, 2021 at 09:28:39PM +0900, Masami Hiramatsu wrote: > > > > > > Record the frame pointer instead of stack address with kretprobe > > > > > > instance as the identifier on the instance list. > > > > > > Since arm64 always enable CONFIG_FRAME_POINTER, we can use the > > > > > > actual frame pointer (x29). > > > > > > > > > > Just to check, why do we need to use the FP rather than SP? It wasn't > > > > > clear to me if that's necessary later in the series, or if I'm missing > > > > > something here. > > > > > > > > Actually, this is for finding correct return address from the per-task > > > > kretprobe instruction list (suppose it as a shadow stack) when it will > > > > be searched in stack-backtracing. At that point, the framepointer will > > > > be a reliable key. > > > > > > Sure, my question was more "why isn't the SP a reliable key?", because both > > > the SP and FP should be balanced at function-entry and function-return > > > time. I'm asking because I think I'm missing a subtlety. > > > > Ah, because SP is not used while unwinding frame. For the kretprobe, > > either FP or SP is OK. But for the stacktrace.c, I can not use SP > > and is easy to change to use FP. :) > > Ah, so this is just so that stacktrace can match the address. For > clarity, would you be happy to add a sentence to the commit message like: > > | This will allow the stacktrace code to find the original return > | address from the FP alone. Yes, I'm happy to update the changelog :) Thanks! > > Thanks, > Mark. -- Masami Hiramatsu <mhiramat@kernel.org>
WARNING: multiple messages have this Message-ID (diff)
From: Masami Hiramatsu <mhiramat@kernel.org> To: Mark Rutland <mark.rutland@arm.com> Cc: Steven Rostedt <rostedt@goodmis.org>, "Naveen N . Rao" <naveen.n.rao@linux.vnet.ibm.com>, Ananth N Mavinakayanahalli <ananth@linux.ibm.com>, Ingo Molnar <mingo@kernel.org>, linux-kernel@vger.kernel.org, Sven Schnelle <svens@linux.ibm.com>, Catalin Marinas <catalin.marinas@arm.com>, Will Deacon <will@kernel.org>, Russell King <linux@armlinux.org.uk>, Nathan Chancellor <nathan@kernel.org>, Nick Desaulniers <ndesaulniers@google.com>, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH 3/8] arm64: kprobes: Record frame pointer with kretprobe instance Date: Thu, 14 Oct 2021 22:50:39 +0900 [thread overview] Message-ID: <20211014225039.b96ff7b7fa86f340ceb50192@kernel.org> (raw) In-Reply-To: <20211014102702.GB13770@C02TD0UTHF1T.local> On Thu, 14 Oct 2021 11:27:02 +0100 Mark Rutland <mark.rutland@arm.com> wrote: > On Thu, Oct 14, 2021 at 07:01:55PM +0900, Masami Hiramatsu wrote: > > On Thu, 14 Oct 2021 10:13:32 +0100 > > Mark Rutland <mark.rutland@arm.com> wrote: > > > > > On Thu, Oct 14, 2021 at 05:04:05PM +0900, Masami Hiramatsu wrote: > > > > On Wed, 13 Oct 2021 11:01:39 +0100 > > > > Mark Rutland <mark.rutland@arm.com> wrote: > > > > > > > > > On Fri, Oct 08, 2021 at 09:28:39PM +0900, Masami Hiramatsu wrote: > > > > > > Record the frame pointer instead of stack address with kretprobe > > > > > > instance as the identifier on the instance list. > > > > > > Since arm64 always enable CONFIG_FRAME_POINTER, we can use the > > > > > > actual frame pointer (x29). > > > > > > > > > > Just to check, why do we need to use the FP rather than SP? It wasn't > > > > > clear to me if that's necessary later in the series, or if I'm missing > > > > > something here. > > > > > > > > Actually, this is for finding correct return address from the per-task > > > > kretprobe instruction list (suppose it as a shadow stack) when it will > > > > be searched in stack-backtracing. At that point, the framepointer will > > > > be a reliable key. > > > > > > Sure, my question was more "why isn't the SP a reliable key?", because both > > > the SP and FP should be balanced at function-entry and function-return > > > time. I'm asking because I think I'm missing a subtlety. > > > > Ah, because SP is not used while unwinding frame. For the kretprobe, > > either FP or SP is OK. But for the stacktrace.c, I can not use SP > > and is easy to change to use FP. :) > > Ah, so this is just so that stacktrace can match the address. For > clarity, would you be happy to add a sentence to the commit message like: > > | This will allow the stacktrace code to find the original return > | address from the FP alone. Yes, I'm happy to update the changelog :) Thanks! > > Thanks, > Mark. -- Masami Hiramatsu <mhiramat@kernel.org> _______________________________________________ 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:[~2021-10-14 13:50 UTC|newest] Thread overview: 54+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-10-08 12:28 [PATCH 0/8] kprobes: Make KUnit and add stacktrace on kretprobe tests Masami Hiramatsu 2021-10-08 12:28 ` Masami Hiramatsu 2021-10-08 12:28 ` [PATCH 1/8] kprobes: convert tests to kunit Masami Hiramatsu 2021-10-08 12:28 ` Masami Hiramatsu 2021-10-08 12:28 ` [PATCH 2/8] kprobes: Add a test case for stacktrace from kretprobe handler Masami Hiramatsu 2021-10-08 12:28 ` Masami Hiramatsu 2021-10-08 12:28 ` [PATCH 3/8] arm64: kprobes: Record frame pointer with kretprobe instance Masami Hiramatsu 2021-10-08 12:28 ` Masami Hiramatsu 2021-10-13 8:14 ` Will Deacon 2021-10-13 8:14 ` Will Deacon 2021-10-13 10:01 ` Mark Rutland 2021-10-13 10:01 ` Mark Rutland 2021-10-14 8:04 ` Masami Hiramatsu 2021-10-14 8:04 ` Masami Hiramatsu 2021-10-14 9:13 ` Mark Rutland 2021-10-14 9:13 ` Mark Rutland 2021-10-14 10:01 ` Masami Hiramatsu 2021-10-14 10:01 ` Masami Hiramatsu 2021-10-14 10:27 ` Mark Rutland 2021-10-14 10:27 ` Mark Rutland 2021-10-14 13:50 ` Masami Hiramatsu [this message] 2021-10-14 13:50 ` Masami Hiramatsu 2021-10-08 12:28 ` [PATCH 4/8] arm64: kprobes: Make a frame pointer on __kretprobe_trampoline Masami Hiramatsu 2021-10-08 12:28 ` Masami Hiramatsu 2021-10-13 8:14 ` Will Deacon 2021-10-13 8:14 ` Will Deacon 2021-10-08 12:28 ` [PATCH 5/8] arm64: Recover kretprobe modified return address in stacktrace Masami Hiramatsu 2021-10-08 12:28 ` Masami Hiramatsu 2021-10-13 8:14 ` Will Deacon 2021-10-13 8:14 ` Will Deacon 2021-10-14 8:05 ` Masami Hiramatsu 2021-10-14 8:05 ` Masami Hiramatsu 2021-10-13 10:13 ` Mark Rutland 2021-10-13 10:13 ` Mark Rutland 2021-10-14 9:57 ` Masami Hiramatsu 2021-10-14 9:57 ` Masami Hiramatsu 2021-10-08 12:29 ` [PATCH 6/8] ARM: clang: Do not relay on lr register for stacktrace Masami Hiramatsu 2021-10-08 12:29 ` Masami Hiramatsu 2021-10-11 18:45 ` Nick Desaulniers 2021-10-11 18:45 ` Nick Desaulniers 2021-10-12 14:18 ` Masami Hiramatsu 2021-10-12 14:18 ` Masami Hiramatsu 2021-10-13 19:54 ` Nick Desaulniers 2021-10-13 19:54 ` Nick Desaulniers 2021-10-14 16:53 ` Russell King (Oracle) 2021-10-14 16:53 ` Russell King (Oracle) 2021-10-15 0:18 ` Masami Hiramatsu 2021-10-15 0:18 ` Masami Hiramatsu 2021-10-08 12:29 ` [PATCH 7/8] ARM: kprobes: Make a frame pointer on __kretprobe_trampoline Masami Hiramatsu 2021-10-08 12:29 ` Masami Hiramatsu 2021-10-11 19:06 ` Nick Desaulniers 2021-10-11 19:06 ` Nick Desaulniers 2021-10-08 12:29 ` [PATCH 8/8] ARM: Recover kretprobe modified return address in stacktrace Masami Hiramatsu 2021-10-08 12:29 ` Masami Hiramatsu
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