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From: "Madhavan T. Venkataraman" <madvenka@linux.microsoft.com>
To: Mark Rutland <mark.rutland@arm.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, jmorris@namei.org,
	linux-arm-kernel@lists.infradead.org,
	live-patching@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v10 08/11] arm64: Rename unwinder functions, prevent them from being traced and kprobed
Date: Wed, 27 Oct 2021 15:07:09 -0500	[thread overview]
Message-ID: <88b9f9fb-155f-da97-b8ef-755eaf2a4af9@linux.microsoft.com> (raw)
In-Reply-To: <20211027175325.GC58503@C02TD0UTHF1T.local>



On 10/27/21 12:53 PM, Mark Rutland wrote:
> On Thu, Oct 14, 2021 at 09:58:44PM -0500, madvenka@linux.microsoft.com wrote:
>> From: "Madhavan T. Venkataraman" <madvenka@linux.microsoft.com>
>>
>> Rename unwinder functions for consistency and better naming.
>>
>> 	- Rename start_backtrace() to unwind_start().
>> 	- Rename unwind_frame() to unwind_next().
>> 	- Rename walk_stackframe() to unwind().
> 
> This looks good to me.
> 

Thanks.

> Could we split this from the krpbes/tracing changes? I think this stands
> on it's own, and (as below) the kprobes/tracing changes need some more
> explanation, and would make sense as a separate patch.
> 

OK. I will split the patches.

>> Prevent the following unwinder functions from being traced:
>>
>> 	- unwind_start()
>> 	- unwind_next()
>>
>> 	unwind() is already prevented from being traced.
> 
> This could do with an explanation in the commis message as to why we
> need to do this. If this is fixing a latent issue, it should be in a
> preparatory patch that we can backport.
> 
> I dug into this a bit, and from taking a look, we prohibited ftrace in commit:
> 
>   0c32706dac1b0a72 ("arm64: stacktrace: avoid tracing arch_stack_walk()")
> 
> ... which is just one special case of graph return stack unbalancing,
> and should be addressed by using HAVE_FUNCTION_GRAPH_RET_ADDR_PTR, so
> with the patch making us use HAVE_FUNCTION_GRAPH_RET_ADDR_PTR, that's
> no longer necessary.
> 
> So we no longer seem to have a specific reason to prohibit ftrace
> here.
> 

OK, I will think about this and add a comment.

>> Prevent the following unwinder functions from being kprobed:
>>
>> 	- unwind_start()
>>
>> 	unwind_next() and unwind() are already prevented from being kprobed.
> 
> Likewise, I think this needs some explanation. From diggin, we
> prohibited kprobes in commit:
> 
>   ee07b93e7721ccd5 ("arm64: unwind: Prohibit probing on return_address()")
> 
> ... and the commit message says we need to do this because this is
> (transitively) called by trace_hardirqs_off(), which is kprobes
> blacklisted, but doesn't explain the actual problem this results in.
> 

OK. I will think about this and add a comment.

> AFAICT x86 directly uses __builtin_return_address() here, but that won't
> recover rewritten addresses, which seems like a bug (or at least a
> limitation) on x86, assuming I've read that correctly.
> 

OK.

Thanks,

Madhavan

  reply	other threads:[~2021-10-27 20:07 UTC|newest]

Thread overview: 52+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <c05ce30dcc9be1bd6b5e24a2ca8fe1d66246980b>
2021-10-15  2:34 ` [PATCH v9 00/11] arm64: Reorganize the unwinder and implement stack trace reliability checks madvenka
2021-10-15  2:34   ` [PATCH v9 01/11] arm64: Select STACKTRACE in arch/arm64/Kconfig madvenka
2021-10-15  2:34   ` [PATCH v9 10/11] arm64: Introduce stack trace reliability checks in the unwinder madvenka
2021-10-15  2:34   ` [PATCH v9 11/11] arm64: Create a list of SYM_CODE functions, check return PC against list madvenka
2021-10-15  2:34   ` [PATCH v9 02/11] arm64: Make perf_callchain_kernel() use arch_stack_walk() madvenka
2021-10-15  2:34   ` [PATCH v9 03/11] arm64: Make get_wchan() " madvenka
2021-10-15  2:34   ` [PATCH v9 04/11] arm64: Make return_address() " madvenka
2021-10-15  2:34   ` [PATCH v9 05/11] arm64: Make dump_stacktrace() " madvenka
2021-10-15  2:34   ` [PATCH v9 06/11] arm64: Make profile_pc() " madvenka
2021-10-15  2:34   ` [PATCH v9 07/11] arm64: Call stack_backtrace() only from within walk_stackframe() madvenka
2021-10-15  2:34   ` [PATCH v9 08/11] arm64: Rename unwinder functions, prevent them from being traced and kprobed madvenka
2021-10-15  2:34   ` [PATCH v9 09/11] arm64: Make the unwind loop in unwind() similar to other architectures madvenka
2021-10-15  2:53   ` [PATCH v9 00/11] arm64: Reorganize the unwinder and implement stack trace reliability checks Madhavan T. Venkataraman
2021-10-15  2:58 ` [PATCH v10 " madvenka
2021-10-15  2:58   ` [PATCH v10 01/11] arm64: Select STACKTRACE in arch/arm64/Kconfig madvenka
2021-10-15 18:28     ` Mark Brown
2021-10-21 12:28       ` Madhavan T. Venkataraman
2021-10-22 18:02     ` Mark Rutland
2021-11-12 17:44       ` Mark Rutland
2021-11-14 16:15         ` Madhavan T. Venkataraman
2021-10-15  2:58   ` [PATCH v10 02/11] arm64: Make perf_callchain_kernel() use arch_stack_walk() madvenka
2021-10-20 14:59     ` Mark Brown
2021-10-21 12:28       ` Madhavan T. Venkataraman
2021-10-22 18:11     ` Mark Rutland
2021-10-23 12:49       ` Madhavan T. Venkataraman
2021-10-15  2:58   ` [PATCH v10 03/11] arm64: Make get_wchan() " madvenka
2021-10-20 16:10     ` Mark Brown
2021-10-21 12:30       ` Madhavan T. Venkataraman
2021-10-15  2:58   ` [PATCH v10 04/11] arm64: Make return_address() " madvenka
2021-10-20 15:03     ` Mark Brown
2021-10-21 12:29       ` Madhavan T. Venkataraman
2021-10-22 18:51     ` Mark Rutland
2021-10-23 12:51       ` Madhavan T. Venkataraman
2021-10-15  2:58   ` [PATCH v10 05/11] arm64: Make dump_stacktrace() " madvenka
2021-10-25 16:49     ` Mark Rutland
2021-10-26 12:05       ` Mark Rutland
2021-10-27 16:09         ` Madhavan T. Venkataraman
2021-10-15  2:58   ` [PATCH v10 06/11] arm64: Make profile_pc() " madvenka
2021-10-25  2:18     ` nobuta.keiya
2021-10-27 16:10       ` Madhavan T. Venkataraman
2021-10-27 13:32     ` Mark Rutland
2021-10-27 16:15       ` Madhavan T. Venkataraman
2021-10-15  2:58   ` [PATCH v10 07/11] arm64: Call stack_backtrace() only from within walk_stackframe() madvenka
2021-10-15  2:58   ` [PATCH v10 08/11] arm64: Rename unwinder functions, prevent them from being traced and kprobed madvenka
2021-10-27 17:53     ` Mark Rutland
2021-10-27 20:07       ` Madhavan T. Venkataraman [this message]
2021-10-15  2:58   ` [PATCH v10 09/11] arm64: Make the unwind loop in unwind() similar to other architectures madvenka
2021-10-15  2:58   ` [PATCH v10 10/11] arm64: Introduce stack trace reliability checks in the unwinder madvenka
2021-11-04 12:39     ` nobuta.keiya
2021-11-10  3:13       ` Madhavan T. Venkataraman
2021-10-15  2:58   ` [PATCH v10 11/11] arm64: Create a list of SYM_CODE functions, check return PC against list madvenka
2021-10-15 17:00   ` [PATCH v10 00/11] arm64: Reorganize the unwinder and implement stack trace reliability checks Madhavan T. Venkataraman

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