Re: [PATCH v7 7/7] ARM: Enable KASan for ARM

[Ard Biesheuvel]

On Fri, 17 Jan 2020 at 23:52, Florian Fainelli <f.fainelli@xxxxxxxxx> wrote:
>
> From: Andrey Ryabinin <ryabinin@xxxxxxxxxxxxx>
>
> This patch enables the kernel address sanitizer for ARM. XIP_KERNEL has
> not been tested and is therefore not allowed.
>
> Acked-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
> Tested-by: Linus Walleij <linus.walleij@xxxxxxxxxx>
> Signed-off-by: Abbott Liu <liuwenliang@xxxxxxxxxx>
> Signed-off-by: Florian Fainelli <f.fainelli@xxxxxxxxx>
> ---
>  Documentation/dev-tools/kasan.rst     | 4 ++--
>  arch/arm/Kconfig                      | 9 +++++++++
>  arch/arm/boot/compressed/Makefile     | 1 +
>  drivers/firmware/efi/libstub/Makefile | 3 ++-
>  4 files changed, 14 insertions(+), 3 deletions(-)
>
> diff --git a/Documentation/dev-tools/kasan.rst b/Documentation/dev-tools/kasan.rst
> index e4d66e7c50de..6acd949989c3 100644
> --- a/Documentation/dev-tools/kasan.rst
> +++ b/Documentation/dev-tools/kasan.rst
> @@ -21,8 +21,8 @@ global variables yet.
>
>  Tag-based KASAN is only supported in Clang and requires version 7.0.0 or later.
>
> -Currently generic KASAN is supported for the x86_64, arm64, xtensa and s390
> -architectures, and tag-based KASAN is supported only for arm64.
> +Currently generic KASAN is supported for the x86_64, arm, arm64, xtensa and
> +s390 architectures, and tag-based KASAN is supported only for arm64.
>
>  Usage
>  -----
> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> index 96dab76da3b3..70a7eb50984e 100644
> --- a/arch/arm/Kconfig
> +++ b/arch/arm/Kconfig
> @@ -65,6 +65,7 @@ config ARM
>         select HAVE_ARCH_BITREVERSE if (CPU_32v7M || CPU_32v7) && !CPU_32v6
>         select HAVE_ARCH_JUMP_LABEL if !XIP_KERNEL && !CPU_ENDIAN_BE32 && MMU
>         select HAVE_ARCH_KGDB if !CPU_ENDIAN_BE32 && MMU
> +       select HAVE_ARCH_KASAN if MMU && !XIP_KERNEL
>         select HAVE_ARCH_MMAP_RND_BITS if MMU
>         select HAVE_ARCH_SECCOMP_FILTER if AEABI && !OABI_COMPAT
>         select HAVE_ARCH_THREAD_STRUCT_WHITELIST
> @@ -212,6 +213,14 @@ config ARCH_MAY_HAVE_PC_FDC
>  config ZONE_DMA
>         bool
>
> +config KASAN_SHADOW_OFFSET
> +       hex
> +       depends on KASAN
> +       default 0x1f000000 if PAGE_OFFSET=0x40000000
> +       default 0x5f000000 if PAGE_OFFSET=0x80000000
> +       default 0x9f000000 if PAGE_OFFSET=0xC0000000
> +       default 0xffffffff
> +
>  config ARCH_SUPPORTS_UPROBES
>         def_bool y
>
> diff --git a/arch/arm/boot/compressed/Makefile b/arch/arm/boot/compressed/Makefile
> index 83991a0447fa..efda24b00a44 100644
> --- a/arch/arm/boot/compressed/Makefile
> +++ b/arch/arm/boot/compressed/Makefile
> @@ -25,6 +25,7 @@ endif
>
>  GCOV_PROFILE           := n
>  KASAN_SANITIZE         := n
> +CFLAGS_KERNEL          += -D__SANITIZE_ADDRESS__
>
>  # Prevents link failures: __sanitizer_cov_trace_pc() is not linked in.
>  KCOV_INSTRUMENT                := n
> diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile
> index c35f893897e1..c8b36824189b 100644
> --- a/drivers/firmware/efi/libstub/Makefile
> +++ b/drivers/firmware/efi/libstub/Makefile
> @@ -20,7 +20,8 @@ cflags-$(CONFIG_ARM64)                := $(subst $(CC_FLAGS_FTRACE),,$(KBUILD_CFLAGS)) \
>                                    -fpie $(DISABLE_STACKLEAK_PLUGIN)
>  cflags-$(CONFIG_ARM)           := $(subst $(CC_FLAGS_FTRACE),,$(KBUILD_CFLAGS)) \
>                                    -fno-builtin -fpic \
> -                                  $(call cc-option,-mno-single-pic-base)
> +                                  $(call cc-option,-mno-single-pic-base) \
> +                                  -D__SANITIZE_ADDRESS__
>

I am not too crazy about this need to unconditionally 'enable' KASAN
on the command line like this, in order to be able to disable it again
when CONFIG_KASAN=y.

Could we instead add something like this at the top of
arch/arm/boot/compressed/string.c?

#ifdef CONFIG_KASAN
#undef memcpy
#undef memmove
#undef memset
void *__memcpy(void *__dest, __const void *__src, size_t __n) __alias(memcpy);
void *__memmove(void *__dest, __const void *__src, size_t count)
__alias(memmove);
void *__memset(void *s, int c, size_t count) __alias(memset);
#endif