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
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next prev parent reply other threads:[~2021-04-09 17:25 UTC|newest]
Thread overview: 33+ 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 ` [RFC PATCH v2 1/4] arm64: Implement infrastructure for " madvenka
2021-04-08 15:15 ` Mark Brown
2021-04-08 17:17 ` Mark Brown
2021-04-08 19:30 ` Madhavan T. Venkataraman
2021-04-08 23:30 ` Madhavan T. Venkataraman
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 ` [RFC PATCH v2 3/4] arm64: Detect FTRACE cases that make the stack trace unreliable madvenka
2021-04-08 16:58 ` Mark Brown
2021-04-08 19:23 ` Madhavan T. Venkataraman
2021-04-09 11:31 ` Mark Brown
2021-04-09 14:02 ` Madhavan T. Venkataraman
2021-04-09 12:27 ` Mark Rutland
2021-04-09 17:23 ` Madhavan T. Venkataraman [this message]
2021-04-05 20:43 ` [RFC PATCH v2 4/4] arm64: Mark stack trace as unreliable if kretprobed functions are present madvenka
2021-04-09 12:09 ` [RFC PATCH v2 0/4] arm64: Implement stack trace reliability checks Mark Rutland
2021-04-09 17:16 ` Madhavan T. Venkataraman
2021-04-09 21:37 ` Josh Poimboeuf
2021-04-09 22:05 ` Madhavan T. Venkataraman
2021-04-09 22:32 ` Josh Poimboeuf
2021-04-09 22:53 ` Josh Poimboeuf
2021-04-11 17:54 ` Madhavan T. Venkataraman
2021-04-12 16:59 ` Mark Brown
2021-04-13 22:53 ` Josh Poimboeuf
2021-04-14 12:24 ` Mark Brown
2021-04-12 17:36 ` Mark Brown
2021-04-12 19:55 ` Madhavan T. Venkataraman
2021-04-13 11:02 ` Mark Brown
2021-04-14 10:23 ` Madhavan T. Venkataraman
2021-04-14 12:35 ` Mark Brown
2021-04-16 14:43 ` Madhavan T. Venkataraman
2021-04-16 15:36 ` Mark Brown
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