linux-hardening - Re: [PATCH 05/15] x86: Implement function

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Date:   Sat, 17 Apr 2021 00:13:29 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Sami Tolvanen <samitolvanen@...gle.com>,
        Borislav Petkov <bp@...en8.de>
Cc:     X86 ML <x86@...nel.org>, Kees Cook <keescook@...omium.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,
        LKML <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>
Subject: Re: [PATCH 05/15] x86: Implement function_nocfi

On Fri, Apr 16 2021 at 14:49, Sami Tolvanen wrote:
> On Fri, Apr 16, 2021 at 2:18 PM Borislav Petkov <bp@...en8.de> wrote:
>> In file included from ./include/linux/ftrace.h:22:0,
>>                  from ./include/linux/init_task.h:9,
>>                  from init/init_task.c:2:
>> ./include/linux/ftrace.h: In function ‘ftrace_init_nop’:
>> ./arch/x86/include/asm/ftrace.h:9:40: error: implicit declaration of function ‘function_nocfi’ [-Werror=implicit-function-declaration]
>
> This is defined in linux-next, but I do see another issue, which I'll
> fix in v2. Note that CFI_CLANG itself cannot be selected on 32-bit
> x86.

Sure and because of that it's overrated to make sure that it does not
break the build. I know, sekurity ...

But aside of that when looking at the rest of the series, then I really
have to ask whether the only way to address this is to make a large
amount of code unreadable like this:

-	wrmsrl(MSR_LSTAR, (unsigned long)entry_SYSCALL_64);
+	wrmsrl(MSR_LSTAR, (unsigned long)function_nocfi(entry_SYSCALL_64));

plus a gazillion of similar changes.

This is unreadable garbage.

Thanks,

        tglx