[PATCH] x86/hw_breakpoints: Return -EINVAL in default case in hw_breakpoint_arch_parse

[PATCH] x86/hw_breakpoints: Return -EINVAL in default case in hw_breakpoint_arch_parse

[Nathan Chancellor]

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@google.com>
Signed-off-by: Nathan Chancellor <natechancellor@gmail.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

Re: [PATCH] x86/hw_breakpoints: Return -EINVAL in default case in hw_breakpoint_arch_parse

[Nick Desaulniers]

On Thu, Mar 7, 2019 at 1:28 PM Nathan Chancellor
<natechancellor@gmail.com> 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.

And the call site just bubbles up return codes anyways.  Thanks for sending.
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>

>
> Link: https://github.com/ClangBuiltLinux/linux/issues/392
> Suggested-by: Nick Desaulniers <ndesaulniers@google.com>
> Signed-off-by: Nathan Chancellor <natechancellor@gmail.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
>


-- 
Thanks,
~Nick Desaulniers

Re: [PATCH] x86/hw_breakpoints: Return -EINVAL in default case in hw_breakpoint_arch_parse

[Nathan Chancellor]

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@google.com>
> Signed-off-by: Nathan Chancellor <natechancellor@gmail.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

[tip:x86/urgent] x86/hw_breakpoints: Make default case in hw_breakpoint_arch_parse() return an error

[tip-bot for Nathan Chancellor]

Commit-ID:  e898e69d6b9475bf123f99b3c5d1a67bb7cb2361
Gitweb:     https://git.kernel.org/tip/e898e69d6b9475bf123f99b3c5d1a67bb7cb2361
Author:     Nathan Chancellor <natechancellor@gmail.com>
AuthorDate: Thu, 7 Mar 2019 14:27:56 -0700
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Fri, 22 Mar 2019 17:08:17 +0100

x86/hw_breakpoints: Make default case in hw_breakpoint_arch_parse() return an error

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]

The default cannot be reached because arch_build_bp_info() initializes
hw->len to one of the specified cases. Nevertheless the warning is valid
and returning -EINVAL makes sure that this cannot be broken by future
modifications.

Suggested-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: clang-built-linux@googlegroups.com
Link: https://github.com/ClangBuiltLinux/linux/issues/392
Link: https://lkml.kernel.org/r/20190307212756.4648-1-natechancellor@gmail.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;
 	}
 
 	/*