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From: Mark Brown <broonie@kernel.org>
To: "Madhavan T. Venkataraman" <madvenka@linux.microsoft.com>
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 17:34:06 +0100	[thread overview]
Message-ID: <20210505163406.GB4541@sirena.org.uk> (raw)
In-Reply-To: <1bd2b177-509a-21d9-e349-9b2388db45eb@linux.microsoft.com>

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On Tue, May 04, 2021 at 02:03:14PM -0500, Madhavan T. Venkataraman wrote:
> On 5/4/21 11:05 AM, Mark Brown wrote:

> >> @@ -118,9 +160,21 @@ int notrace unwind_frame(struct task_struct *tsk, struct stackframe *frame)
> >>  			return -EINVAL;
> >>  		frame->pc = ret_stack->ret;
> >>  		frame->pc = ptrauth_strip_insn_pac(frame->pc);
> >> +		return 0;
> >>  	}

> > Do we not need to look up the range of the restored pc and validate
> > what's being pointed to here?  It's not immediately obvious why we do
> > the lookup before handling the function graph tracer, especially given
> > that we never look at the result and there's now a return added skipping
> > further reliability checks.  At the very least I think this needs some
> > additional comments so the code is more obvious.

> I want sym_code_ranges[] to contain both unwindable and non-unwindable ranges.
> Unwindable ranges will be special ranges such as the return_to_handler() and
> kretprobe_trampoline() functions for which the unwinder has (or will have)
> special code to unwind. So, the lookup_range() has to happen before the
> function graph code. Please look at the last patch in the series for
> the fix for the above function graph code.

That sounds reasonable but like I say should probably be called out in
the code so it's clear to people working with it.

> On the question of "should the original return address be checked against
> sym_code_ranges[]?" - I assumed that if there is a function graph trace on a
> function, it had to be an ftraceable function. It would not be a part
> of sym_code_ranges[]. Is that a wrong assumption on my part?

I can't think of any cases where it wouldn't be right now, but it seems
easier to just do a redundant check than to have the assumption in the
code and have to think about if it's missing.

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  parent reply	other threads:[~2021-05-05 16:44 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
2021-05-06 13:45               ` Mark Brown
2021-05-06 15:21                 ` Madhavan T. Venkataraman
2021-05-05 16:34         ` Mark Brown [this message]
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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