linux-kernel - Re: [PATCH v3 15/16] x86, kprobes: Fix optprobe_template

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Message-ID: <202109141240.4843E7A9@keescook>
Date:   Tue, 14 Sep 2021 12:40:08 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Sami Tolvanen <samitolvanen@...gle.com>
Cc:     x86@...nel.org, Josh Poimboeuf <jpoimboe@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Sedat Dilek <sedat.dilek@...il.com>,
        linux-hardening@...r.kernel.org, linux-kernel@...r.kernel.org,
        clang-built-linux@...glegroups.com
Subject: Re: [PATCH v3 15/16] x86, kprobes: Fix optprobe_template_func type
 mismatch

On Tue, Sep 14, 2021 at 12:10:44PM -0700, Sami Tolvanen wrote:
> The optprobe_template_func symbol is defined in inline assembly,
> but it's not marked global, which conflicts with the C declaration
> needed for STACK_FRAME_NON_STANDARD and confuses the compiler when
> CONFIG_CFI_CLANG is enabled.
> 
> Marking the symbol global would make the compiler happy, but as the
> compiler also generates a CFI jump table entry for all address-taken
> functions, the jump table ends up containing a jump to the .rodata
> section where optprobe_template_func resides, which results in an
> objtool warning.
> 
> Use ASM_STACK_FRAME_NON_STANDARD instead to avoid both issues.
> 
> Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>

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

-- 
Kees Cook