linux-kernel - Re: [RFC PATCH 12/17] gcc-plugins: objtool: Add plugin to detect switch table on arm64

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Message-ID: <2935D431-6329-4BC8-A871-A019CD3F6EB1@arm.com>
Date:   Tue, 9 Feb 2021 16:30:17 +0000
From:   Daniel Kiss <Daniel.Kiss@....com>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
CC:     Julien Thierry <jthierry@...hat.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Mark Brown <broonie@...nel.org>,
        Catalin Marinas <Catalin.Marinas@....com>,
        Kees Cook <keescook@...omium.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-efi <linux-efi@...r.kernel.org>,
        "linux-hardening@...r.kernel.org" <linux-hardening@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Mark Rutland <Mark.Rutland@....com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Peter Zijlstra <peterz@...radead.org>,
        Raphaël Gault <Raphael.Gault@....com>,
        Will Deacon <will@...nel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Bill Wendling <morbo@...gle.com>,
        "swine@...gle.com" <swine@...gle.com>,
        "yonghyun@...gle.com" <yonghyun@...gle.com>
Subject: Re: [RFC PATCH 12/17] gcc-plugins: objtool: Add plugin to detect
 switch table on arm64



> On 3 Feb 2021, at 00:01, Nick Desaulniers <ndesaulniers@...gle.com> wrote:
> 
> I wonder if PAC or BTI also make this slightly more complex?  PAC at
> least has implications for unwinders, IIUC.

BTI has effect on the jump target\case because a landing pad is required for each and every target.
As I see that would not hurt here.

The unwinder shall take care of the PAC signed return address if reads the LR from the stack.
DWARF contains an entry where the LR is got signed\authenticated.

I’m wondering would be simpler or possible to transform the DWARD to ORC.