linux-kernel - Re: [PATCH] x86/hw_breakpoints: Return -EINVAL in default case in hw_breakpoint_arch

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Date:   Wed, 20 Mar 2019 12:10:57 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>
Cc:     "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, clang-built-linux@...glegroups.com,
        Nick Desaulniers <ndesaulniers@...gle.com>
Subject: Re: [PATCH] x86/hw_breakpoints: Return -EINVAL in default case in
 hw_breakpoint_arch_parse

On Thu, Mar 07, 2019 at 02:27:56PM -0700, Nathan Chancellor wrote:
> When building with -Wsometimes-uninitialized, Clang warns:
> 
> arch/x86/kernel/hw_breakpoint.c:355:2: warning: variable 'align' is used
> uninitialized whenever switch default is taken
> [-Wsometimes-uninitialized]
> 
> It's not wrong but we can see that arch_build_bp_info will only ever
> initialize hw->len to one of the specified switch cases. We can easily
> silence Clang by just returning -EINVAL in the default case so that we
> can never use align without initializing it first.
> 
> Link: https://github.com/ClangBuiltLinux/linux/issues/392
> Suggested-by: Nick Desaulniers <ndesaulniers@...gle.com>
> Signed-off-by: Nathan Chancellor <natechancellor@...il.com>
> ---
>  arch/x86/kernel/hw_breakpoint.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/arch/x86/kernel/hw_breakpoint.c b/arch/x86/kernel/hw_breakpoint.c
> index ff9bfd40429e..d73083021002 100644
> --- a/arch/x86/kernel/hw_breakpoint.c
> +++ b/arch/x86/kernel/hw_breakpoint.c
> @@ -354,6 +354,7 @@ int hw_breakpoint_arch_parse(struct perf_event *bp,
>  #endif
>  	default:
>  		WARN_ON_ONCE(1);
> +		return -EINVAL;
>  	}
>  
>  	/*
> -- 
> 2.21.0
> 

Gentle ping (if there was a response to this, I didn't receive it). I
know I sent it in the middle of a merge window so I get if it slipped
through the cracks.

Thanks,
Nathan