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

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Message-Id: <20190307212756.4648-1-natechancellor@gmail.com>
Date:   Thu,  7 Mar 2019 14:27:56 -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>,
        Nathan Chancellor <natechancellor@...il.com>
Subject: [PATCH] x86/hw_breakpoints: Return -EINVAL in default case in hw_breakpoint_arch_parse

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