linux-kernel - Re: [PATCH v2 08/11] arm64/static_call: Fix static call CFI violations

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Message-ID: <20230322141933.GD2357380@hirez.programming.kicks-ass.net>
Date:   Wed, 22 Mar 2023 15:19:33 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Mark Rutland <mark.rutland@....com>
Cc:     Josh Poimboeuf <jpoimboe@...nel.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org, Jason Baron <jbaron@...mai.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ard Biesheuvel <ardb@...nel.org>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Will McVicker <willmcvicker@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 08/11] arm64/static_call: Fix static call CFI
 violations

On Wed, Mar 22, 2023 at 12:22:07PM +0000, Mark Rutland wrote:
> On Tue, Mar 21, 2023 at 09:00:14PM -0700, Josh Poimboeuf wrote:

> > +++ b/arch/arm64/include/asm/static_call.h
> > @@ -0,0 +1,29 @@
> > +/* SPDX-License-Identifier: GPL-2.0 */
> > +#ifndef _ASM_ARM64_STATIC_CALL_H
> > +#define _ASM_ARM64_STATIC_CALL_H
> > +
> > +/*
> > + * Make a dummy reference to a function pointer in C to force the compiler to
> > + * emit a __kcfi_typeid_ symbol for asm to use.
> > + */
> > +#define GEN_CFI_SYM(func)						\
> > +	static typeof(func) __used __section(".discard.cfi") *__UNIQUE_ID(cfi) = func
> > +
> > +
> > +/* Generate a CFI-compliant static call NOP function */
> > +#define __ARCH_DEFINE_STATIC_CALL_CFI(name, insns)			\
> > +	asm(".align 4						\n"	\

Should this ^ be:

	__ALIGN_STR "\n" \

> > +	    ".word __kcfi_typeid_" name "			\n"	\
> > +	    ".globl " name "					\n"	\
> > +	    name ":						\n"	\
> > +	    "bti c						\n"	\
> > +	    insns "						\n"	\
> > +	    "ret						\n"	\
> > +	    ".type " name ", @function				\n"	\
> > +	    ".size " name ", . - " name "			\n")

Also, Mark, I think you can remove __ALIGN and __ALIGN_STR from
arch/arm64/include/linkage.h they're very similar to the generic one.