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Message-ID: <20220418161145.hj3ahxqjdgqd3qn2@treble>
Date: Mon, 18 Apr 2022 09:11:45 -0700
From: Josh Poimboeuf <jpoimboe@...hat.com>
To: Chen Zhongjin <chenzhongjin@...wei.com>
Cc: "Madhavan T. Venkataraman" <madvenka@...ux.microsoft.com>,
mark.rutland@....com, broonie@...nel.org, ardb@...nel.org,
nobuta.keiya@...itsu.com, sjitindarsingh@...il.com,
catalin.marinas@....com, will@...nel.org, jmorris@...ei.org,
linux-arm-kernel@...ts.infradead.org,
live-patching@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v1 0/9] arm64: livepatch: Use DWARF Call Frame
Information for frame pointer validation
On Mon, Apr 18, 2022 at 08:28:33PM +0800, Chen Zhongjin wrote:
> Hi Josh,
>
> IIUC, ORC on x86 can make reliable stack unwind for this scenario
> because objtool validates BP state.
>
> I'm thinking that on arm64 there's no guarantee that LR will be pushed
> onto stack. When we meet similar scenario on arm64, we should recover
> (LR, FP) on pt_regs and continue to unwind the stack. And this is
> reliable only after we validate (LR, FP).
>
> So should we track LR on arm64 additionally as track BP on x86? Or can
> we just treat (LR, FP) as a pair? because as I know they are always set
> up together.
Does the arm64 unwinder have a way to detect kernel pt_regs on the
stack? If so, the simplest solution is to mark all stacks with kernel
regs as unreliable. That's what the x86 FP unwinder does.
--
Josh
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