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From:   Sami Tolvanen <samitolvanen@google.com>
Date:   Mon, 25 Jul 2022 17:09:57 -0700
Message-ID: <CABCJKucWbN15tH=zJ7HFeNnOPB3v7S=2=oL3pmp89OHOM2=oYw@mail.gmail.com>
Subject: Re: [RFC PATCH v3 20/20] x86: Add support for CONFIG_CFI_CLANG
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     LKML <linux-kernel@vger.kernel.org>,
        Kees Cook <keescook@chromium.org>,
        Josh Poimboeuf <jpoimboe@redhat.com>, X86 ML <x86@kernel.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Nathan Chancellor <nathan@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Joao Moreira <joao@overdrivepizza.com>,
        Sedat Dilek <sedat.dilek@gmail.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        linux-hardening@vger.kernel.org,
        linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
        llvm@lists.linux.dev
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On Sat, Jul 23, 2022 at 4:21 AM Peter Zijlstra <peterz@infradead.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