Re: [PATCH] arm64: fix CONFIG_KASAN_SW_TAGS && CONFIG_KASAN_INLINE (was: Re: [PATCH V5 03/12] arm64: kasan: Switch to using) KASAN_SHADOW_OFFSET

From: Mark Rutland <mark.rutland@arm•com>
To: Will Deacon <will@kernel•org>, Andrey Ryabinin <aryabinin@virtuozzo•com>
Cc: crecklin@redhat•com, ard.biesheuvel@linaro•org,
	catalin.marinas@arm•com, bhsharma@redhat•com,
	Steve Capper <steve.capper@arm•com>,
	maz@kernel•org, linux-arm-kernel@lists•infradead.org
Subject: Re: [PATCH] arm64: fix CONFIG_KASAN_SW_TAGS && CONFIG_KASAN_INLINE (was: Re: [PATCH V5 03/12] arm64: kasan: Switch to using) KASAN_SHADOW_OFFSET
Date: Wed, 14 Aug 2019 17:03:24 +0100	[thread overview]
Message-ID: <20190814160324.GE51963@lakrids.cambridge.arm.com> (raw)
In-Reply-To: <20190814155711.ldwot7ezrrqjlswc@willie-the-truck>

On Wed, Aug 14, 2019 at 04:57:11PM +0100, Will Deacon wrote:
> On Wed, Aug 14, 2019 at 04:20:18PM +0100, Mark Rutland wrote:
> > On Wed, Aug 07, 2019 at 04:55:15PM +0100, Steve Capper wrote:
> > > diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
> > > index b2400f9c1213..2b7db0d41498 100644
> > > --- a/arch/arm64/Makefile
> > > +++ b/arch/arm64/Makefile
> > > @@ -126,14 +126,6 @@ KBUILD_CFLAGS += -DKASAN_SHADOW_SCALE_SHIFT=$(KASAN_SHADOW_SCALE_SHIFT)
> > >  KBUILD_CPPFLAGS += -DKASAN_SHADOW_SCALE_SHIFT=$(KASAN_SHADOW_SCALE_SHIFT)
> > >  KBUILD_AFLAGS += -DKASAN_SHADOW_SCALE_SHIFT=$(KASAN_SHADOW_SCALE_SHIFT)
> > >  
> > > -# KASAN_SHADOW_OFFSET = VA_START + (1 << (VA_BITS - KASAN_SHADOW_SCALE_SHIFT))
> > > -#				 - (1 << (64 - KASAN_SHADOW_SCALE_SHIFT))
> > > -# in 32-bit arithmetic
> > > -KASAN_SHADOW_OFFSET := $(shell printf "0x%08x00000000\n" $$(( \
> > > -	(0xffffffff & (-1 << ($(CONFIG_ARM64_VA_BITS) - 1 - 32))) \
> > > -	+ (1 << ($(CONFIG_ARM64_VA_BITS) - 32 - $(KASAN_SHADOW_SCALE_SHIFT))) \
> > > -	- (1 << (64 - 32 - $(KASAN_SHADOW_SCALE_SHIFT))) )) )
> > > -
> > >  export	TEXT_OFFSET GZFLAGS
> > >  
> > >  core-y		+= arch/arm64/kernel/ arch/arm64/mm/
> > 
> > I've just spotted this breaks build using CONFIG_KASAN_SW_TAGS &&
> > CONFIG_KASAN_INLINE, as scripts/Makefile.kasan only propagates
> > CONFIG_KASAN_SHADOW_OFFSET into KASAN_SHADOW_OFFSET when
> > CONFIG_KASAN_GENERIC is selected, but consumes KASAN_SHADOW_OFFSET
> > regardless.
> > 
> > I think that's by accident rather than by design, but to
> > minimize/localize the fixup, how about the below? I can send a cleanup
> > patch for scripts/Makefile.kasan later.
> 
> How much work is that? I've dropped this stuff from -next for now, so we
> have time to fix it properly as long as it's not going to take weeks.

I wrote it first, so no effort; patch below.

Andrey, would you be happy with this?

Thanks,
Mark.

---->8----
From ecdf60051a850f817d98f84ae9011afa2311b8f1 Mon Sep 17 00:00:00 2001
From: Mark Rutland <mark.rutland@arm•com>
Date: Wed, 14 Aug 2019 15:31:57 +0100
Subject: [PATCH] kasan/arm64: fix CONFIG_KASAN_SW_TAGS && KASAN_INLINE

The generic Makefile.kasan propagates CONFIG_KASAN_SHADOW_OFFSET into
KASAN_SHADOW_OFFSET, but only does so for CONFIG_KASAN_GENERIC.

Since commit:

  6bd1d0be0e97936d ("arm64: kasan: Switch to using KASAN_SHADOW_OFFSET")

... arm64 defines CONFIG_KASAN_SHADOW_OFFSET in Kconfig rather than
defining KASAN_SHADOW_OFFSET in a Makefile. Thus, if
CONFIG_KASAN_SW_TAGS && KASAN_INLINE are selected, we get build time
splats due to KASAN_SHADOW_OFFSET not being set:

| [mark@lakrids:~/src/linux]% usellvm 8.0.1 usekorg 8.1.0  make ARCH=arm64 CROSS_COMPILE=aarch64-linux- CC=clang
| scripts/kconfig/conf  --syncconfig Kconfig
|   CC      scripts/mod/empty.o
| clang (LLVM option parsing): for the -hwasan-mapping-offset option: '' value invalid for uint argument!
| scripts/Makefile.build:273: recipe for target 'scripts/mod/empty.o' failed
| make[1]: *** [scripts/mod/empty.o] Error 1
| Makefile:1123: recipe for target 'prepare0' failed
| make: *** [prepare0] Error 2

Let's fix this by always propagating CONFIG_KASAN_SHADOW_OFFSET into
KASAN_SHADOW_OFFSET if CONFIG_KASAN is selected, moving the existing
common definition of +CFLAGS_KASAN_NOSANITIZE to the top of
Makefile.kasan.

Signed-off-by: Mark Rutland <mark.rutland@arm•com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo•com>
Cc: Catalin Marinas <catalin.marinas@arm•com>
Cc: Steve Capper <steve.capper@arm•com>
Cc: Will Deacon <will@kernel•org>
---
 scripts/Makefile.kasan | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/scripts/Makefile.kasan b/scripts/Makefile.kasan
index 6410bd22fe38..03757cc60e06 100644
--- a/scripts/Makefile.kasan
+++ b/scripts/Makefile.kasan
@@ -1,4 +1,9 @@
 # SPDX-License-Identifier: GPL-2.0
+ifdef CONFIG_KASAN
+CFLAGS_KASAN_NOSANITIZE := -fno-builtin
+KASAN_SHADOW_OFFSET ?= $(CONFIG_KASAN_SHADOW_OFFSET)
+endif
+
 ifdef CONFIG_KASAN_GENERIC
 
 ifdef CONFIG_KASAN_INLINE
@@ -7,8 +12,6 @@ else
 	call_threshold := 0
 endif
 
-KASAN_SHADOW_OFFSET ?= $(CONFIG_KASAN_SHADOW_OFFSET)
-
 CFLAGS_KASAN_MINIMAL := -fsanitize=kernel-address
 
 cc-param = $(call cc-option, -mllvm -$(1), $(call cc-option, --param $(1)))
@@ -45,7 +48,3 @@ CFLAGS_KASAN := -fsanitize=kernel-hwaddress \
 		$(instrumentation_flags)
 
 endif # CONFIG_KASAN_SW_TAGS
-
-ifdef CONFIG_KASAN
-CFLAGS_KASAN_NOSANITIZE := -fno-builtin
-endif
-- 
2.11.0


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