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Date:   Wed, 5 May 2021 17:46:48 +0100
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
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On Tue, May 04, 2021 at 02:32:35PM -0500, Madhavan T. Venkataraman wrote:

> If you prefer, I could do something like this:
>=20
> check_pc:
> 	if (!__kernel_text_address(frame->pc))
> 		frame->reliable =3D false;
>=20
> 	range =3D lookup_range(frame->pc);
>=20
> #ifdef CONFIG_FUNCTION_GRAPH_TRACER
> 	if (tsk->ret_stack &&
> 		frame->pc =3D=3D (unsigned long)return_to_handler) {
> 		...
> 		frame->pc =3D ret_stack->ret;
> 		frame->pc =3D 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.

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