linux-hardening - Re: [RFC PATCH v3 20/20] x86: Add support for CONFIG_CFI

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Date:   Mon, 25 Jul 2022 17:09:57 -0700
From:   Sami Tolvanen <samitolvanen@...gle.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Kees Cook <keescook@...omium.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>, X86 ML <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 <linux-arm-kernel@...ts.infradead.org>,
        llvm@...ts.linux.dev
Subject: Re: [RFC PATCH v3 20/20] x86: Add support for CONFIG_CFI_CLANG

On Sat, Jul 23, 2022 at 4:21 AM Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Fri, Jun 10, 2022 at 04:35:13PM -0700, Sami Tolvanen wrote:
>
> > +#ifdef CONFIG_CFI_CLANG
> > +#define __CFI_TYPE(name)                                     \
> > +     .fill 7, 1, 0xCC ASM_NL                                 \
> > +     SYM_START(__cfi_##name, SYM_L_LOCAL, SYM_A_NONE)        \
> > +     int3 ASM_NL                                             \
> > +     int3 ASM_NL                                             \
> > +     mov __kcfi_typeid_##name, %eax ASM_NL                   \
> > +     int3 ASM_NL                                             \
> > +     int3 ASM_NL                                             \
> > +     SYM_FUNC_END(__cfi_##name)
> > +#endif
>
> Like said on IRC yesterday, this doesn't generate the right mov
> encoding.
>
>         .byte 0xb8 ; .long __kcfi_typeid_##name ;               \
>
> works. Your LLVM tree already has the ZExt patch you gave me yesterday
> to fix up the linker fallout from this change.

Indeed, I updated my kernel tree and confirmed that this fixes the
issue. Thanks for pointing it out.

Sami