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From:   Marco Elver <elver@google.com>
Date:   Tue, 19 Apr 2022 12:15:36 +0200
Message-ID: <CANpmjNNW0kLf2Ou6i_dNeRLO=Qrru4bOEfJ=be=Dfig4wnQ67g@mail.gmail.com>
Subject: Re: [PATCH] xtensa: enable KCSAN
To:     Max Filippov <jcmvbkbc@gmail.com>
Cc:     linux-xtensa@linux-xtensa.org, Chris Zankel <chris@zankel.net>,
        linux-kernel@vger.kernel.org, Dmitry Vyukov <dvyukov@google.com>,
        kasan-dev@googlegroups.com
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Nice to see this happen!

On Sat, 16 Apr 2022 at 10:14, Max Filippov <jcmvbkbc@gmail.com> wrote:
>
> Prefix arch-specific barrier macros with '__' to make use of instrumented
> generic macros.
> Prefix arch-specific bitops with 'arch_' to make use of instrumented
> generic functions.

> Provide stubs for 64-bit atomics when building with KCSAN.

The stubs are the only thing I don't understand. More elaboration on
why this is required would be useful (maybe there's another way to
solve?).

> Disable KCSAN instrumentation in arch/xtensa/boot.

Given you went for barrier instrumentation, I assume you tested with a
CONFIG_KCSAN_STRICT=y config? Did the kcsan_test pass?

> Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
> ---
>  arch/xtensa/Kconfig               |  1 +
>  arch/xtensa/boot/lib/Makefile     |  1 +
>  arch/xtensa/include/asm/barrier.h |  6 ++--
>  arch/xtensa/include/asm/bitops.h  | 10 +++---
>  arch/xtensa/lib/Makefile          |  2 ++
>  arch/xtensa/lib/kcsan-stubs.c     | 54 +++++++++++++++++++++++++++++++
>  6 files changed, 67 insertions(+), 7 deletions(-)
>  create mode 100644 arch/xtensa/lib/kcsan-stubs.c
>
> diff --git a/arch/xtensa/Kconfig b/arch/xtensa/Kconfig
> index 797355c142b3..c87f5ab493d9 100644
> --- a/arch/xtensa/Kconfig
> +++ b/arch/xtensa/Kconfig
> @@ -29,6 +29,7 @@ config XTENSA
>         select HAVE_ARCH_AUDITSYSCALL
>         select HAVE_ARCH_JUMP_LABEL if !XIP_KERNEL
>         select HAVE_ARCH_KASAN if MMU && !XIP_KERNEL
> +       select HAVE_ARCH_KCSAN
>         select HAVE_ARCH_SECCOMP_FILTER
>         select HAVE_ARCH_TRACEHOOK
>         select HAVE_CONTEXT_TRACKING
> diff --git a/arch/xtensa/boot/lib/Makefile b/arch/xtensa/boot/lib/Makefile
> index e3d717c7bfa1..162d10af36f3 100644
> --- a/arch/xtensa/boot/lib/Makefile
> +++ b/arch/xtensa/boot/lib/Makefile
> @@ -16,6 +16,7 @@ CFLAGS_REMOVE_inffast.o = -pg
>  endif
>
>  KASAN_SANITIZE := n
> +KCSAN_SANITIZE := n
>
>  CFLAGS_REMOVE_inflate.o += -fstack-protector -fstack-protector-strong
>  CFLAGS_REMOVE_zmem.o += -fstack-protector -fstack-protector-strong
> diff --git a/arch/xtensa/include/asm/barrier.h b/arch/xtensa/include/asm/barrier.h
> index d6f8d4ddc2bc..a22d4bb08159 100644
> --- a/arch/xtensa/include/asm/barrier.h
> +++ b/arch/xtensa/include/asm/barrier.h
> @@ -11,9 +11,9 @@
>
>  #include <asm/core.h>
>
> -#define mb()  ({ __asm__ __volatile__("memw" : : : "memory"); })
> -#define rmb() barrier()
> -#define wmb() mb()
> +#define __mb()  ({ __asm__ __volatile__("memw" : : : "memory"); })
> +#define __rmb() barrier()
> +#define __wmb() mb()
>
>  #if XCHAL_HAVE_S32C1I
>  #define __smp_mb__before_atomic()              barrier()
> diff --git a/arch/xtensa/include/asm/bitops.h b/arch/xtensa/include/asm/bitops.h
> index cd225896c40f..e02ec5833389 100644
> --- a/arch/xtensa/include/asm/bitops.h
> +++ b/arch/xtensa/include/asm/bitops.h
> @@ -99,7 +99,7 @@ static inline unsigned long __fls(unsigned long word)
>  #if XCHAL_HAVE_EXCLUSIVE
>
>  #define BIT_OP(op, insn, inv)                                          \
> -static inline void op##_bit(unsigned int bit, volatile unsigned long *p)\
> +static inline void arch_##op##_bit(unsigned int bit, volatile unsigned long *p)\
>  {                                                                      \
>         unsigned long tmp;                                              \
>         unsigned long mask = 1UL << (bit & 31);                         \
> @@ -119,7 +119,7 @@ static inline void op##_bit(unsigned int bit, volatile unsigned long *p)\
>
>  #define TEST_AND_BIT_OP(op, insn, inv)                                 \
>  static inline int                                                      \
> -test_and_##op##_bit(unsigned int bit, volatile unsigned long *p)       \
> +arch_test_and_##op##_bit(unsigned int bit, volatile unsigned long *p)  \
>  {                                                                      \
>         unsigned long tmp, value;                                       \
>         unsigned long mask = 1UL << (bit & 31);                         \
> @@ -142,7 +142,7 @@ test_and_##op##_bit(unsigned int bit, volatile unsigned long *p)    \
>  #elif XCHAL_HAVE_S32C1I
>
>  #define BIT_OP(op, insn, inv)                                          \
> -static inline void op##_bit(unsigned int bit, volatile unsigned long *p)\
> +static inline void arch_##op##_bit(unsigned int bit, volatile unsigned long *p)\
>  {                                                                      \
>         unsigned long tmp, value;                                       \
>         unsigned long mask = 1UL << (bit & 31);                         \
> @@ -163,7 +163,7 @@ static inline void op##_bit(unsigned int bit, volatile unsigned long *p)\
>
>  #define TEST_AND_BIT_OP(op, insn, inv)                                 \
>  static inline int                                                      \
> -test_and_##op##_bit(unsigned int bit, volatile unsigned long *p)       \
> +arch_test_and_##op##_bit(unsigned int bit, volatile unsigned long *p)  \
>  {                                                                      \
>         unsigned long tmp, value;                                       \
>         unsigned long mask = 1UL << (bit & 31);                         \
> @@ -205,6 +205,8 @@ BIT_OPS(change, "xor", )
>  #undef BIT_OP
>  #undef TEST_AND_BIT_OP
>
> +#include <asm-generic/bitops/instrumented-atomic.h>
> +
>  #include <asm-generic/bitops/le.h>
>
>  #include <asm-generic/bitops/ext2-atomic-setbit.h>
> diff --git a/arch/xtensa/lib/Makefile b/arch/xtensa/lib/Makefile
> index 5848c133f7ea..d4e9c397e3fd 100644
> --- a/arch/xtensa/lib/Makefile
> +++ b/arch/xtensa/lib/Makefile
> @@ -8,3 +8,5 @@ lib-y   += memcopy.o memset.o checksum.o \
>            divsi3.o udivsi3.o modsi3.o umodsi3.o mulsi3.o \
>            usercopy.o strncpy_user.o strnlen_user.o
>  lib-$(CONFIG_PCI) += pci-auto.o
> +lib-$(CONFIG_KCSAN) += kcsan-stubs.o
> +KCSAN_SANITIZE_kcsan-stubs.o := n
> diff --git a/arch/xtensa/lib/kcsan-stubs.c b/arch/xtensa/lib/kcsan-stubs.c
> new file mode 100644
> index 000000000000..2b08faa62b86
> --- /dev/null
> +++ b/arch/xtensa/lib/kcsan-stubs.c
> @@ -0,0 +1,54 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +#include <linux/bug.h>
> +#include <linux/types.h>
> +
> +void __atomic_store_8(volatile void *p, u64 v, int i)
> +{
> +       BUG();
> +}
> +
> +u64 __atomic_load_8(const volatile void *p, int i)
> +{
> +       BUG();
> +}
> +
> +u64 __atomic_exchange_8(volatile void *p, u64 v, int i)
> +{
> +       BUG();
> +}
> +
> +bool __atomic_compare_exchange_8(volatile void *p1, void *p2, u64 v, bool b, int i1, int i2)
> +{
> +       BUG();
> +}
> +
> +u64 __atomic_fetch_add_8(volatile void *p, u64 v, int i)
> +{
> +       BUG();
> +}
> +
> +u64 __atomic_fetch_sub_8(volatile void *p, u64 v, int i)
> +{
> +       BUG();
> +}
> +
> +u64 __atomic_fetch_and_8(volatile void *p, u64 v, int i)
> +{
> +       BUG();
> +}
> +
> +u64 __atomic_fetch_or_8(volatile void *p, u64 v, int i)
> +{
> +       BUG();
> +}
> +
> +u64 __atomic_fetch_xor_8(volatile void *p, u64 v, int i)
> +{
> +       BUG();
> +}
> +
> +u64 __atomic_fetch_nand_8(volatile void *p, u64 v, int i)
> +{
> +       BUG();
> +}
> --
> 2.30.2
>
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