linux-hardening - Re: [PATCH v4 16/21] objtool: Disable CFI warnings

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Message-ID: <202208311123.CFD2B1B9@keescook>
Date:   Wed, 31 Aug 2022 11:23:34 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Sami Tolvanen <samitolvanen@...gle.com>
Cc:     linux-kernel@...r.kernel.org, Josh Poimboeuf <jpoimboe@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>, x86@...nel.org,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Joao Moreira <joao@...rdrivepizza.com>,
        Sedat Dilek <sedat.dilek@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        linux-hardening@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, llvm@...ts.linux.dev
Subject: Re: [PATCH v4 16/21] objtool: Disable CFI warnings

On Tue, Aug 30, 2022 at 04:31:24PM -0700, Sami Tolvanen wrote:
> The __cfi_ preambles contain a mov instruction that embeds the KCFI
> type identifier in the following format:
> 
>   ; type preamble
>   __cfi_function:
>     mov <id>, %eax
>   function:
>     ...
> 
> While the preamble symbols are STT_FUNC and contain valid
> instructions, they are never executed and always fall through. Skip
> the warning for them.
> 
> .kcfi_traps sections point to CFI traps in text sections. Also skip
> the warning about them referencing !ENDBR instructions.
> 
> Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>

Reviewed-by: Kees Cook <keescook@...omium.org>

-- 
Kees Cook