[PATCH 4.4 31/70] x86/mm/kaslr: Use the _ASM_MUL macro for multiplication to work around Clang incompatibility

Greg Kroah-Hartman
2018-11-26T10:54:45Z

From: Matthias Kaehlcke <mka@chromium.org>

commit 121843eb02a6e2fa30aefab64bfe183c97230c75 upstream.

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
operand.

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 <mka@chromium.org>
Cc: Grant Grundler <grundler@chromium.org>
Cc: Greg Hackmann <ghackmann@google.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Michael Davidson <md@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20170501224741.133938-1-mka@chromium.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
[nc: Apply to aslr.c in get_random_long as the kaslr shift didn't happen
until 4.8 in commit d899a7d146a2]
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/x86/boot/compressed/aslr.c | 3 ++-
arch/x86/include/asm/asm.h | 1 +
2 files changed, 3 insertions(+), 1 deletion(-)

--- a/arch/x86/boot/compressed/aslr.c
+++ b/arch/x86/boot/compressed/aslr.c
@@ -1,5 +1,6 @@
#include "misc.h"

+#include <asm/asm.h>
#include <asm/msr.h>
#include <asm/archrandom.h>
#include <asm/e820.h>
@@ -94,7 +95,7 @@ static unsigned long get_random_long(voi
}

/* Circular multiply for better bit diffusion */
- asm("mul %3"
+ asm(_ASM_MUL "%3"
: "=a" (random), "=d" (raw)
: "a" (random), "rm" (mix_const));
random += raw;
--- 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)