4.9-stable review patch.  If anyone has any objections, please let me know.


From: Matthias Kaehlcke <m...@chromium.org>

[ Upstream commit 121843eb02a6e2fa30aefab64bfe183c97230c75 ]

The constraint "rm" allows the compiler to put mix_const into memory.
When the input operand is a memory location then MUL needs an operand
size suffix, since Clang can't infer the multiplication width from the

Add and use the _ASM_MUL macro which determines the operand size and
resolves to the NUL instruction with the corresponding suffix.

This fixes the following error when building with clang:

  CC      arch/x86/lib/kaslr.o
  /tmp/kaslr-dfe1ad.s: Assembler messages:
  /tmp/kaslr-dfe1ad.s:182: Error: no instruction mnemonic suffix given and no 
register operands; can't size instruction

Signed-off-by: Matthias Kaehlcke <m...@chromium.org>
Cc: Grant Grundler <grund...@chromium.org>
Cc: Greg Hackmann <ghackm...@google.com>
Cc: Kees Cook <keesc...@chromium.org>
Cc: Linus Torvalds <torva...@linux-foundation.org>
Cc: Michael Davidson <m...@google.com>
Cc: Peter Zijlstra <pet...@infradead.org>
Cc: Thomas Gleixner <t...@linutronix.de>
Link: http://lkml.kernel.org/r/20170501224741.133938-1-...@chromium.org
Signed-off-by: Ingo Molnar <mi...@kernel.org>
Signed-off-by: Sasha Levin <alexander.le...@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
 arch/x86/include/asm/asm.h |    1 +
 arch/x86/lib/kaslr.c       |    3 ++-
 2 files changed, 3 insertions(+), 1 deletion(-)

--- a/arch/x86/include/asm/asm.h
+++ b/arch/x86/include/asm/asm.h
@@ -34,6 +34,7 @@
 #define _ASM_ADD       __ASM_SIZE(add)
 #define _ASM_SUB       __ASM_SIZE(sub)
 #define _ASM_XADD      __ASM_SIZE(xadd)
+#define _ASM_MUL       __ASM_SIZE(mul)
 #define _ASM_AX                __ASM_REG(ax)
 #define _ASM_BX                __ASM_REG(bx)
--- a/arch/x86/lib/kaslr.c
+++ b/arch/x86/lib/kaslr.c
@@ -5,6 +5,7 @@
  * kernel starts. This file is included in the compressed kernel and
  * normally linked in the regular.
+#include <asm/asm.h>
 #include <asm/kaslr.h>
 #include <asm/msr.h>
 #include <asm/archrandom.h>
@@ -79,7 +80,7 @@ unsigned long kaslr_get_random_long(cons
        /* Circular multiply for better bit diffusion */
-       asm("mul %3"
+       asm(_ASM_MUL "%3"
            : "=a" (random), "=d" (raw)
            : "a" (random), "rm" (mix_const));
        random += raw;

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