linux-kernel - Re: [PATCH v6 22/25] x86/asm: annotate indirect jumps

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Date:   Wed, 21 Oct 2020 11:32:13 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Sami Tolvanen <samitolvanen@...gle.com>
Cc:     Josh Poimboeuf <jpoimboe@...hat.com>, Jann Horn <jannh@...gle.com>,
        the arch/x86 maintainers <x86@...nel.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Will Deacon <will@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        linux-arch <linux-arch@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-kbuild <linux-kbuild@...r.kernel.org>,
        kernel list <linux-kernel@...r.kernel.org>,
        linux-pci@...r.kernel.org
Subject: Re: [PATCH v6 22/25] x86/asm: annotate indirect jumps

On Wed, Oct 21, 2020 at 10:56:06AM +0200, Peter Zijlstra wrote:

> I do not see these in particular, although I do see a lot of:
> 
>   "sibling call from callable instruction with modified stack frame"

defconfig-build/vmlinux.o: warning: objtool: msr_write()+0x10a: sibling call from callable instruction with modified stack frame
defconfig-build/vmlinux.o: warning: objtool:   msr_write()+0x99: (branch)
defconfig-build/vmlinux.o: warning: objtool:   msr_write()+0x3e: (branch)
defconfig-build/vmlinux.o: warning: objtool:   msr_write()+0x0: <=== (sym)

$ nm defconfig-build/vmlinux.o | grep msr_write
0000000000043250 t msr_write
00000000004289c0 T msr_write
0000000000003056 t msr_write.cold

Below 'fixes' it. So this is also caused by duplicate symbols.

---
diff --git a/arch/x86/lib/msr.c b/arch/x86/lib/msr.c
index 3bd905e10ee2..e36331f8f217 100644
--- a/arch/x86/lib/msr.c
+++ b/arch/x86/lib/msr.c
@@ -48,17 +48,6 @@ int msr_read(u32 msr, struct msr *m)
 	return err;
 }
 
-/**
- * Write an MSR with error handling
- *
- * @msr: MSR to write
- * @m: value to write
- */
-int msr_write(u32 msr, struct msr *m)
-{
-	return wrmsrl_safe(msr, m->q);
-}
-
 static inline int __flip_bit(u32 msr, u8 bit, bool set)
 {
 	struct msr m, m1;
@@ -80,7 +69,7 @@ static inline int __flip_bit(u32 msr, u8 bit, bool set)
 	if (m1.q == m.q)
 		return 0;
 
-	err = msr_write(msr, &m1);
+	err = wrmsr_safe(msr, m1.q);
 	if (err)
 		return err;