From: "Madhavan T. Venkataraman" <madvenka@linux.microsoft.com> To: Mark Rutland <mark.rutland@arm.com> Cc: broonie@kernel.org, jpoimboe@redhat.com, jthierry@redhat.com, catalin.marinas@arm.com, will@kernel.org, linux-arm-kernel@lists.infradead.org, live-patching@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH v2 3/4] arm64: Detect FTRACE cases that make the stack trace unreliable Date: Fri, 9 Apr 2021 12:23:47 -0500 [thread overview] Message-ID: <c57de436-7943-175f-29b2-ed7ebcdc0837@linux.microsoft.com> (raw) In-Reply-To: <20210409122701.GB51636@C02TD0UTHF1T.local> >> Also, the Function Graph Tracer modifies the return address of a traced >> function to a return trampoline to gather tracing data on function return. >> Stack traces taken from that trampoline and functions it calls are >> unreliable as the original return address may not be available in >> that context. Mark the stack trace unreliable accordingly. >> >> Signed-off-by: Madhavan T. Venkataraman <madvenka@linux.microsoft.com> >> --- >> arch/arm64/kernel/entry-ftrace.S | 12 +++++++ >> arch/arm64/kernel/stacktrace.c | 61 ++++++++++++++++++++++++++++++++ >> 2 files changed, 73 insertions(+) >> >> diff --git a/arch/arm64/kernel/entry-ftrace.S b/arch/arm64/kernel/entry-ftrace.S >> index b3e4f9a088b1..1f0714a50c71 100644 >> --- a/arch/arm64/kernel/entry-ftrace.S >> +++ b/arch/arm64/kernel/entry-ftrace.S >> @@ -86,6 +86,18 @@ SYM_CODE_START(ftrace_caller) >> b ftrace_common >> SYM_CODE_END(ftrace_caller) >> >> +/* >> + * A stack trace taken from anywhere in the FTRACE trampoline code should be >> + * considered unreliable as a tracer function (patched at ftrace_call) could >> + * potentially set pt_regs->pc and redirect execution to a function different >> + * than the traced function. E.g., livepatch. > > IIUC the issue here that we have two copies of the pc: one in the regs, > and one in a frame record, and so after the update to the regs, the > frame record is stale. > > This is something that we could fix by having > ftrace_instruction_pointer_set() set both. > Yes. I will look at this. > However, as noted elsewhere there are other issues which mean we'd still > need special unwinding code for this. > The only other cases we have discussed are EL1 exceptions in the ftrace code and the return trampoline for function graph tracing. Is there any other case? Thanks. Madhavan
WARNING: multiple messages have this Message-ID (diff)
From: "Madhavan T. Venkataraman" <madvenka@linux.microsoft.com> To: Mark Rutland <mark.rutland@arm.com> Cc: broonie@kernel.org, jpoimboe@redhat.com, jthierry@redhat.com, catalin.marinas@arm.com, will@kernel.org, linux-arm-kernel@lists.infradead.org, live-patching@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH v2 3/4] arm64: Detect FTRACE cases that make the stack trace unreliable Date: Fri, 9 Apr 2021 12:23:47 -0500 [thread overview] Message-ID: <c57de436-7943-175f-29b2-ed7ebcdc0837@linux.microsoft.com> (raw) In-Reply-To: <20210409122701.GB51636@C02TD0UTHF1T.local> >> Also, the Function Graph Tracer modifies the return address of a traced >> function to a return trampoline to gather tracing data on function return. >> Stack traces taken from that trampoline and functions it calls are >> unreliable as the original return address may not be available in >> that context. Mark the stack trace unreliable accordingly. >> >> Signed-off-by: Madhavan T. Venkataraman <madvenka@linux.microsoft.com> >> --- >> arch/arm64/kernel/entry-ftrace.S | 12 +++++++ >> arch/arm64/kernel/stacktrace.c | 61 ++++++++++++++++++++++++++++++++ >> 2 files changed, 73 insertions(+) >> >> diff --git a/arch/arm64/kernel/entry-ftrace.S b/arch/arm64/kernel/entry-ftrace.S >> index b3e4f9a088b1..1f0714a50c71 100644 >> --- a/arch/arm64/kernel/entry-ftrace.S >> +++ b/arch/arm64/kernel/entry-ftrace.S >> @@ -86,6 +86,18 @@ SYM_CODE_START(ftrace_caller) >> b ftrace_common >> SYM_CODE_END(ftrace_caller) >> >> +/* >> + * A stack trace taken from anywhere in the FTRACE trampoline code should be >> + * considered unreliable as a tracer function (patched at ftrace_call) could >> + * potentially set pt_regs->pc and redirect execution to a function different >> + * than the traced function. E.g., livepatch. > > IIUC the issue here that we have two copies of the pc: one in the regs, > and one in a frame record, and so after the update to the regs, the > frame record is stale. > > This is something that we could fix by having > ftrace_instruction_pointer_set() set both. > Yes. I will look at this. > However, as noted elsewhere there are other issues which mean we'd still > need special unwinding code for this. > The only other cases we have discussed are EL1 exceptions in the ftrace code and the return trampoline for function graph tracing. Is there any other case? Thanks. 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:[~2021-04-09 17:23 UTC|newest] Thread overview: 66+ messages / expand[flat|nested] mbox.gz Atom feed top [not found] <705993ccb34a611c75cdae0a8cb1b40f9b218ebd> 2021-04-05 20:43 ` [RFC PATCH v2 0/4] arm64: Implement stack trace reliability checks madvenka 2021-04-05 20:43 ` madvenka 2021-04-05 20:43 ` [RFC PATCH v2 1/4] arm64: Implement infrastructure for " madvenka 2021-04-05 20:43 ` madvenka 2021-04-08 15:15 ` Mark Brown 2021-04-08 15:15 ` Mark Brown 2021-04-08 17:17 ` Mark Brown 2021-04-08 17:17 ` Mark Brown 2021-04-08 19:30 ` Madhavan T. Venkataraman 2021-04-08 19:30 ` Madhavan T. Venkataraman 2021-04-08 23:30 ` Madhavan T. Venkataraman 2021-04-08 23:30 ` Madhavan T. Venkataraman 2021-04-09 11:57 ` Mark Brown 2021-04-09 11:57 ` Mark Brown 2021-04-05 20:43 ` [RFC PATCH v2 2/4] arm64: Mark a stack trace unreliable if an EL1 exception frame is detected madvenka 2021-04-05 20:43 ` madvenka 2021-04-05 20:43 ` [RFC PATCH v2 3/4] arm64: Detect FTRACE cases that make the stack trace unreliable madvenka 2021-04-05 20:43 ` madvenka 2021-04-08 16:58 ` Mark Brown 2021-04-08 16:58 ` Mark Brown 2021-04-08 19:23 ` Madhavan T. Venkataraman 2021-04-08 19:23 ` Madhavan T. Venkataraman 2021-04-09 11:31 ` Mark Brown 2021-04-09 11:31 ` Mark Brown 2021-04-09 14:02 ` Madhavan T. Venkataraman 2021-04-09 14:02 ` Madhavan T. Venkataraman 2021-04-09 12:27 ` Mark Rutland 2021-04-09 12:27 ` Mark Rutland 2021-04-09 17:23 ` Madhavan T. Venkataraman [this message] 2021-04-09 17:23 ` Madhavan T. Venkataraman 2021-04-05 20:43 ` [RFC PATCH v2 4/4] arm64: Mark stack trace as unreliable if kretprobed functions are present madvenka 2021-04-05 20:43 ` madvenka 2021-04-09 12:09 ` [RFC PATCH v2 0/4] arm64: Implement stack trace reliability checks Mark Rutland 2021-04-09 12:09 ` Mark Rutland 2021-04-09 17:16 ` Madhavan T. Venkataraman 2021-04-09 17:16 ` Madhavan T. Venkataraman 2021-04-09 21:37 ` Josh Poimboeuf 2021-04-09 21:37 ` Josh Poimboeuf 2021-04-09 22:05 ` Madhavan T. Venkataraman 2021-04-09 22:05 ` Madhavan T. Venkataraman 2021-04-09 22:32 ` Josh Poimboeuf 2021-04-09 22:32 ` Josh Poimboeuf 2021-04-09 22:53 ` Josh Poimboeuf 2021-04-09 22:53 ` Josh Poimboeuf 2021-04-11 17:54 ` Madhavan T. Venkataraman 2021-04-11 17:54 ` Madhavan T. Venkataraman 2021-04-12 16:59 ` Mark Brown 2021-04-12 16:59 ` Mark Brown 2021-04-13 22:53 ` Josh Poimboeuf 2021-04-13 22:53 ` Josh Poimboeuf 2021-04-14 12:24 ` Mark Brown 2021-04-14 12:24 ` Mark Brown 2021-04-12 17:36 ` Mark Brown 2021-04-12 17:36 ` Mark Brown 2021-04-12 19:55 ` Madhavan T. Venkataraman 2021-04-12 19:55 ` Madhavan T. Venkataraman 2021-04-13 11:02 ` Mark Brown 2021-04-13 11:02 ` Mark Brown 2021-04-14 10:23 ` Madhavan T. Venkataraman 2021-04-14 10:23 ` Madhavan T. Venkataraman 2021-04-14 12:35 ` Mark Brown 2021-04-14 12:35 ` Mark Brown 2021-04-16 14:43 ` Madhavan T. Venkataraman 2021-04-16 14:43 ` Madhavan T. Venkataraman 2021-04-16 15:36 ` Mark Brown 2021-04-16 15:36 ` Mark Brown
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