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

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Message-ID: <YtvZvYHC1BKzEz1p@worktop.programming.kicks-ass.net>
Date:   Sat, 23 Jul 2022 13:21:33 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Sami Tolvanen <samitolvanen@...gle.com>
Cc:     linux-kernel@...r.kernel.org, Kees Cook <keescook@...omium.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>, 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: [RFC PATCH v3 20/20] x86: Add support for CONFIG_CFI_CLANG

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.