This is a note to let you know that I've just added the patch titled

x86/mm/kaslr: Use the _ASM_MUL macro for multiplication to work around Clang incompatibility

to the 4.9-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: x86-mm-kaslr-use-the-_asm_mul-macro-for-multiplication-to-work-around-clang-incompatibility.patch and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

From foo@baz Mon Apr 9 17:09:24 CEST 2018

From: Matthias Kaehlcke mka@chromium.org Date: Mon, 1 May 2017 15:47:41 -0700 Subject: x86/mm/kaslr: Use the _ASM_MUL macro for multiplication to work around Clang incompatibility

From: Matthias Kaehlcke mka@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 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 Signed-off-by: Sasha Levin alexander.levin@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@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;

Patches currently in stable-queue which might be from mka@chromium.org are

queue-4.9/x86-mm-kaslr-use-the-_asm_mul-macro-for-multiplication-to-work-around-clang-incompatibility.patch