Messages in this thread | | | From | Kees Cook <> | Date | Mon, 1 May 2017 19:08:01 -0700 | Subject | Re: [PATCH v2] x86/mm/kaslr: Use _ASM_MUL macro for multiplication |
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On Mon, May 1, 2017 at 3:47 PM, Matthias Kaehlcke <mka@chromium.org> wrote: > The constraint "rm" allows the compiler to put mix_const into memory. > When the input operand is a memory location mul needs an operand size > suffix, since it 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 'mul' 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>
Acked-by: Kees Cook <keescook@chromium.org>
Thanks for the v2!
-Kees
> --- > Changes in v2: > - updated commit message with additional details > > arch/x86/include/asm/asm.h | 1 + > arch/x86/lib/kaslr.c | 3 ++- > 2 files changed, 3 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/include/asm/asm.h b/arch/x86/include/asm/asm.h > index 7acb51c49fec..7a9df3beb89b 100644 > --- a/arch/x86/include/asm/asm.h > +++ b/arch/x86/include/asm/asm.h > @@ -32,6 +32,7 @@ > #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) > diff --git a/arch/x86/lib/kaslr.c b/arch/x86/lib/kaslr.c > index 121f59c6ee54..0c7fe444dcdd 100644 > --- 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(const char *purpose) > } > > /* Circular multiply for better bit diffusion */ > - asm("mul %3" > + asm(_ASM_MUL "%3" > : "=a" (random), "=d" (raw) > : "a" (random), "rm" (mix_const)); > random += raw; > -- > 2.13.0.rc1.294.g07d810a77f-goog >
-- Kees Cook Pixel Security
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