linux-kernel - Re: [RESEND][patch V3 06/23] bug: Annotate WARN/BUG/stackfail as noinstr safe

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Message-ID: <20200402210115.zpk52dyc6ofg2bve@treble>
Date:   Thu, 2 Apr 2020 16:01:15 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        Paul McKenney <paulmck@...nel.org>,
        "Joel Fernandes (Google)" <joel@...lfernandes.org>,
        "Steven Rostedt (VMware)" <rostedt@...dmis.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Brian Gerst <brgerst@...il.com>,
        Juergen Gross <jgross@...e.com>,
        Alexandre Chartre <alexandre.chartre@...cle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Tom Lendacky <thomas.lendacky@....com>,
        Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org
Subject: Re: [RESEND][patch V3 06/23] bug: Annotate WARN/BUG/stackfail as
 noinstr safe

On Fri, Mar 20, 2020 at 07:00:02PM +0100, Thomas Gleixner wrote:
> Warnings, bugs and stack protection fails from noinstr sections, e.g. low
> level and early entry code, are likely to be fatal.
> 
> Mark them as "safe" to be invoked from noinstr protected code to avoid
> annotating all usage sites. Getting the information out is important.
> 
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> ---
>  arch/x86/include/asm/bug.h |    3 +++
>  include/asm-generic/bug.h  |    9 +++++++--
>  kernel/panic.c             |    4 +++-
>  3 files changed, 13 insertions(+), 3 deletions(-)
> 
> --- a/arch/x86/include/asm/bug.h
> +++ b/arch/x86/include/asm/bug.h
> @@ -70,13 +70,16 @@ do {									\
>  #define HAVE_ARCH_BUG
>  #define BUG()							\
>  do {								\
> +	instr_begin();						\
>  	_BUG_FLAGS(ASM_UD2, 0);					\
>  	unreachable();						\
>  } while (0)

For visual symmetry at least, it seems like this wants an instr_end()
before the unreachable().  Does objtool not like that?

> --- a/include/asm-generic/bug.h
> +++ b/include/asm-generic/bug.h
> @@ -83,14 +83,19 @@ extern __printf(4, 5)
>  void warn_slowpath_fmt(const char *file, const int line, unsigned taint,
>  		       const char *fmt, ...);
>  #define __WARN()		__WARN_printf(TAINT_WARN, NULL)
> -#define __WARN_printf(taint, arg...)					\
> -	warn_slowpath_fmt(__FILE__, __LINE__, taint, arg)
> +#define __WARN_printf(taint, arg...) do {				\
> +	instr_begin();							\
> +	warn_slowpath_fmt(__FILE__, __LINE__, taint, arg);		\
> +	instr_end();							\
> +	while (0)

Missing a '}' before the 'while'?

-- 
Josh