linux-kernel - Re: [PATCH -tip v3 1/2] kcov: Make runtime functions noinstr-compatible

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Date:   Wed, 17 Jun 2020 17:19:28 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Marco Elver <elver@...gle.com>
Cc:     Dmitry Vyukov <dvyukov@...gle.com>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Mark Rutland <mark.rutland@....com>,
        Borislav Petkov <bp@...en8.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Alexander Potapenko <glider@...gle.com>,
        kasan-dev <kasan-dev@...glegroups.com>,
        LKML <linux-kernel@...r.kernel.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>, ndesaulniers@...gle.com
Subject: Re: [PATCH -tip v3 1/2] kcov: Make runtime functions
 noinstr-compatible

On Wed, Jun 17, 2020 at 04:49:49PM +0200, Peter Zijlstra wrote:

> I had the below, except of course that yields another objtool
> complaint, and I was still looking at that.

This cures it.

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 5fbb90a80d239..fe0d6f1b28d7c 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -2746,7 +2746,7 @@ int check(const char *_objname, bool orc)
 
 	INIT_LIST_HEAD(&file.insn_list);
 	hash_init(file.insn_hash);
-	file.c_file = find_section_by_name(file.elf, ".comment");
+	file.c_file = !vmlinux && find_section_by_name(file.elf, ".comment");
 	file.ignore_unreachables = no_unreachable;
 	file.hints = false;


> diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
> index af75109485c26..a7d1570905727 100644
> --- a/arch/x86/kernel/traps.c
> +++ b/arch/x86/kernel/traps.c
> @@ -690,13 +690,13 @@ struct bad_iret_stack *fixup_bad_iret(struct bad_iret_stack *s)
>  		(struct bad_iret_stack *)__this_cpu_read(cpu_tss_rw.x86_tss.sp0) - 1;
>  
>  	/* Copy the IRET target to the temporary storage. */
> -	memcpy(&tmp.regs.ip, (void *)s->regs.sp, 5*8);
> +	__memcpy(&tmp.regs.ip, (void *)s->regs.sp, 5*8);
>  
>  	/* Copy the remainder of the stack from the current stack. */
> -	memcpy(&tmp, s, offsetof(struct bad_iret_stack, regs.ip));
> +	__memcpy(&tmp, s, offsetof(struct bad_iret_stack, regs.ip));
>  
>  	/* Update the entry stack */
> -	memcpy(new_stack, &tmp, sizeof(tmp));
> +	__memcpy(new_stack, &tmp, sizeof(tmp));
>  
>  	BUG_ON(!user_mode(&new_stack->regs));
>  	return new_stack;
> diff --git a/arch/x86/lib/memcpy_64.S b/arch/x86/lib/memcpy_64.S
> index 56b243b14c3a2..bbcc05bcefadb 100644
> --- a/arch/x86/lib/memcpy_64.S
> +++ b/arch/x86/lib/memcpy_64.S
> @@ -8,6 +8,8 @@
>  #include <asm/alternative-asm.h>
>  #include <asm/export.h>
>  
> +.pushsection .noinstr.text, "ax"
> +
>  /*
>   * We build a jump to memcpy_orig by default which gets NOPped out on
>   * the majority of x86 CPUs which set REP_GOOD. In addition, CPUs which
> @@ -184,6 +186,8 @@ SYM_FUNC_START_LOCAL(memcpy_orig)
>  	retq
>  SYM_FUNC_END(memcpy_orig)
>  
> +.popsection
> +
>  #ifndef CONFIG_UML
>  
>  MCSAFE_TEST_CTL