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

[Ard Biesheuvel]

(+ Linus)

On Fri, 10 Apr 2020 at 12:45, Ard Biesheuvel <ardb@xxxxxxxxxx> wrote:
>
> 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
>
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