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: Will Deacon <will@kernel.org>
To: Mark Rutland <mark.rutland@arm.com>
Cc: crecklin@redhat.com, ard.biesheuvel@linaro.org,
	catalin.marinas@arm.com, bhsharma@redhat.com,
	Steve Capper <steve.capper@arm.com>,
	kasan-dev@googlegroups.com, glider@google.com,
	dvyukov@google.com, maz@kernel.org,
	Andrey Ryabinin <aryabinin@virtuozzo.com>,
	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: Thu, 15 Aug 2019 13:09:09 +0100	[thread overview]
Message-ID: <20190815120908.kboyqfnr2fivuva4@willie-the-truck> (raw)
In-Reply-To: <20190814160324.GE51963@lakrids.cambridge.arm.com>

[+more kasan people and the kasan-dev list]

On Wed, Aug 14, 2019 at 05:03:24PM +0100, Mark Rutland wrote:
> 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.

The patch looks fine to me, but I'd like an Ack from one of the KASAN
folks before I queue this via the arm64 tree (where support for 52-bit
virtual addressing in the kernel [1] depends on this being fixed).

Patch is quoted below. Please can somebody take a look?

Thanks,

Will

[1] https://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git/log/?h=for-next/52-bit-kva

> 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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