linux-kernel - [PATCH] x86/retpoline: Fix NOSPEC

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Date:   Tue,  9 Jan 2018 16:31:39 -0800
From:   Andi Kleen <andi@...stfloor.org>
To:     tglx@...utronix.de
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        torvalds@...ux-foundation.org, dwmw@...zon.co.uk, pjt@...gle.com,
        luto@...nel.org, peterz@...radead.org, thomas.lendacky@....com,
        tim.c.chen@...ux.intel.com, gregkh@...ux-foundation.org,
        dave.hansen@...el.com, jikos@...nel.org,
        Andi Kleen <ak@...ux.intel.com>
Subject: [PATCH] x86/retpoline: Fix NOSPEC_JMP for tip

From: Andi Kleen <ak@...ux.intel.com>

With the latest tip x86/pti I get oopses when booting
a 64bit VM in qemu with RETPOLINE/gcc7 and PTI enabled.

The following patch fixes it for me. Something doesn't
seem to work with ALTERNATIVE_2. It adds only a few bytes
more code, so seems acceptable.

Signed-off-by: Andi Kleen <ak@...ux.intel.com>
---
 arch/x86/include/asm/nospec-branch.h | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h
index 8ddf8513550e..eea6340a0abb 100644
--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -46,9 +46,8 @@
  */
 .macro JMP_NOSPEC reg:req
 #ifdef CONFIG_RETPOLINE
-	ALTERNATIVE_2 __stringify(jmp *\reg),				\
-		__stringify(RETPOLINE_JMP \reg), X86_FEATURE_RETPOLINE,	\
-		__stringify(lfence; jmp *\reg), X86_FEATURE_RETPOLINE_AMD
+	ALTERNATIVE "", __stringify(lfence; jmp *\reg), X86_FEATURE_RETPOLINE_AMD
+	ALTERNATIVE __stringify(jmp *\reg), __stringify(RETPOLINE_JMP \reg), X86_FEATURE_RETPOLINE
 #else
 	jmp	*\reg
 #endif
-- 
2.14.3