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From: "Madhavan T. Venkataraman" <madvenka@linux.microsoft.com>
To: Mark Brown <broonie@kernel.org>
Cc: jpoimboe@redhat.com, mark.rutland@arm.com, jthierry@redhat.com,
	catalin.marinas@arm.com, will@kernel.org, jmorris@namei.org,
	pasha.tatashin@soleen.com, linux-arm-kernel@lists.infradead.org,
	live-patching@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH v3 2/4] arm64: Check the return PC against unreliable code sections
Date: Wed, 5 May 2021 13:50:23 -0500	[thread overview]
Message-ID: <8ea6a81a-2e19-f752-408c-21dea1078f9b@linux.microsoft.com> (raw)
In-Reply-To: <9781011e-2d99-7f46-592c-621c66ea66c3@linux.microsoft.com>



On 5/5/21 1:48 PM, Madhavan T. Venkataraman wrote:
> 
> 
> On 5/5/21 11:46 AM, Mark Brown wrote:
>> On Tue, May 04, 2021 at 02:32:35PM -0500, Madhavan T. Venkataraman wrote:
>>
>>> If you prefer, I could do something like this:
>>>
>>> check_pc:
>>> 	if (!__kernel_text_address(frame->pc))
>>> 		frame->reliable = false;
>>>
>>> 	range = lookup_range(frame->pc);
>>>
>>> #ifdef CONFIG_FUNCTION_GRAPH_TRACER
>>> 	if (tsk->ret_stack &&
>>> 		frame->pc == (unsigned long)return_to_handler) {
>>> 		...
>>> 		frame->pc = ret_stack->ret;
>>> 		frame->pc = ptrauth_strip_insn_pac(frame->pc);
>>> 		goto check_pc;
>>> 	}
>>> #endif /* CONFIG_FUNCTION_GRAPH_TRACER */
>>
>>> Is that acceptable?
>>
>> I think that works even if it's hard to love the goto, might want some
>> defensiveness to ensure we can't somehow end up in an infinite loop with
>> a sufficiently badly formed stack.
>>
> 
> I could do something like this:
> 
> - Move all frame->pc checking code into a function called check_frame_pc().
> 
> 	bool	check_frame_pc(frame)
> 	{
> 		Do all the checks including function graph
> 		return frame->pc changed
> 	}
> 
> - Then, in unwind_frame()
> 
> unwind_frame()
> {
> 	int	i;
> 	...
> 
> 	for (i = 0; i < MAX_CHECKS; i++) {
> 		if (!check_frame(tsk, frame))

Small typo in the last statement - It should be check_frame_pc().

Sorry.

Madhavan

> 			break;
> 	}
> 
> 	if (i == MAX_CHECKS)
> 		frame->reliable = false;
> 	return 0;
> }
> 
> The above would take care of future cases like kretprobe_trampoline().
> 
> If this is acceptable, then the only question is - what should be the value of
> MAX_CHECKS (I will rename it to something more appropriate)?
> 
> Madhavan
> 

  reply	other threads:[~2021-05-05 18:50 UTC|newest]

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <65cf4dfbc439b010b50a0c46ec500432acde86d6>
2021-05-03 17:36 ` [RFC PATCH v3 0/4] arm64: Stack trace reliability checks in the unwinder madvenka
2021-05-03 17:36   ` [RFC PATCH v3 1/4] arm64: Introduce stack " madvenka
2021-05-04 15:50     ` Mark Brown
2021-05-04 19:14       ` Madhavan T. Venkataraman
2021-05-04 21:52     ` Josh Poimboeuf
2021-05-04 23:13       ` Madhavan T. Venkataraman
2021-05-05  0:07         ` Josh Poimboeuf
2021-05-05  0:21           ` Madhavan T. Venkataraman
2021-05-03 17:36   ` [RFC PATCH v3 2/4] arm64: Check the return PC against unreliable code sections madvenka
2021-05-04 16:05     ` Mark Brown
2021-05-04 19:03       ` Madhavan T. Venkataraman
2021-05-04 19:32         ` Madhavan T. Venkataraman
2021-05-05 16:46           ` Mark Brown
2021-05-05 18:48             ` Madhavan T. Venkataraman
2021-05-05 18:50               ` Madhavan T. Venkataraman [this message]
2021-05-06 13:45               ` Mark Brown
2021-05-06 15:21                 ` Madhavan T. Venkataraman
2021-05-05 16:34         ` Mark Brown
2021-05-05 17:51           ` Madhavan T. Venkataraman
2021-05-05 19:30     ` Ard Biesheuvel
2021-05-05 20:00       ` Madhavan T. Venkataraman
2021-05-03 17:36   ` [RFC PATCH v3 3/4] arm64: Handle miscellaneous functions in .text and .init.text madvenka
2021-05-06 14:12     ` Mark Brown
2021-05-06 15:30       ` Madhavan T. Venkataraman
2021-05-06 15:32         ` Madhavan T. Venkataraman
2021-05-06 15:44           ` Mark Brown
2021-05-06 15:56             ` Madhavan T. Venkataraman
2021-05-06 15:37         ` Mark Brown
2021-05-06 15:57           ` Madhavan T. Venkataraman
2021-05-03 17:36   ` [RFC PATCH v3 4/4] arm64: Handle funtion graph tracer better in the unwinder madvenka
2021-05-06 14:43     ` Mark Brown
2021-05-06 15:20       ` Madhavan T. Venkataraman

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