linux-kernel - Re: [PATCH v3] arm64: Enable KCSAN

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Date:   Thu, 2 Dec 2021 15:36:06 +0100
From:   Marco Elver <elver@...gle.com>
To:     Kefeng Wang <wangkefeng.wang@...wei.com>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        mark.rutland@....com
Subject: Re: [PATCH v3] arm64: Enable KCSAN

On Thu, 2 Dec 2021 at 15:23, Kefeng Wang <wangkefeng.wang@...wei.com> wrote:
>
> This patch enables KCSAN for arm64, with updates to build rules
> to not use KCSAN for several incompatible compilation units.
>
> Resent GCC version(at least GCC10) made outline-atomics as the

s/Resent/Recent/

> default option(unlike Clang), which will cause linker errors
> for kernel/kcsan/core.o. Disables the out-of-line atomics by
> no-outline-atomics to fix the linker errors.
>
> Meanwhile, as Mark said[1], there is a specific issue on arm64
> about ARM64_BTI with Clang 11 if KCSAN enabled, which is fixed
> by Clang 12, add CLANG_VERSION check. And also some latent issues
> are need to be fixed which isn't just a KCSAN problem, we make
> the KCSAN depends on EXPERT for now.
>
> Tested selftest and kcsan_test(built with GCC11 and Clang 13),
> and all passed.
>
> [1] https://lkml.org/lkml/2021/12/1/354

Please use lore/kernel.org permalinks. For this one it'd be:
https://lkml.kernel.org/r/YadiUPpJ0gADbiHQ@FVFF77S0Q05N

(But I think if this is the final version of the patch, hopefully a
maintainer can amend the commit message.)

> Signed-off-by: Kefeng Wang <wangkefeng.wang@...wei.com>

Acked-by: Marco Elver <elver@...gle.com> # kernel/kcsan

is still valid, given nothing changed there. I leave the rest to Mark.

Thanks,
-- Marco

> ---
> Tested on Qemu with clang 13 / gcc 11, based on 5.16-rc3.
>
> [    0.221518] kcsan: enabled early
> [    0.222422] kcsan: strict mode configured
> ...
> [    5.839223] kcsan: selftest: 3/3 tests passed
> ...
> [  517.895102] # kcsan: pass:24 fail:0 skip:0 total:24
> [  517.896393] # Totals: pass:168 fail:0 skip:0 total:168
> [  517.897502] ok 1 - kcsan
>
> v3:
> - add EXPERT and CLANG_VERSION depends suggested by Mark Rutland
> v2:
> - tested on GCC11 and disable outline-atomics for kernel/kcsan/core.c
>   suggested by Marco Elver
>
>  arch/arm64/Kconfig               | 1 +
>  arch/arm64/kernel/vdso/Makefile  | 1 +
>  arch/arm64/kvm/hyp/nvhe/Makefile | 1 +
>  kernel/kcsan/Makefile            | 1 +
>  4 files changed, 4 insertions(+)
>
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 4ff73299f8a9..3a7b17742cde 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -150,6 +150,7 @@ config ARM64
>         select HAVE_ARCH_KASAN_VMALLOC if HAVE_ARCH_KASAN
>         select HAVE_ARCH_KASAN_SW_TAGS if HAVE_ARCH_KASAN
>         select HAVE_ARCH_KASAN_HW_TAGS if (HAVE_ARCH_KASAN && ARM64_MTE)
> +       select HAVE_ARCH_KCSAN if EXPERT && (CC_IS_GCC || CLANG_VERSION >= 120000)
>         select HAVE_ARCH_KFENCE
>         select HAVE_ARCH_KGDB
>         select HAVE_ARCH_MMAP_RND_BITS
> diff --git a/arch/arm64/kernel/vdso/Makefile b/arch/arm64/kernel/vdso/Makefile
> index 700767dfd221..60813497a381 100644
> --- a/arch/arm64/kernel/vdso/Makefile
> +++ b/arch/arm64/kernel/vdso/Makefile
> @@ -32,6 +32,7 @@ ccflags-y += -DDISABLE_BRANCH_PROFILING -DBUILD_VDSO
>  CFLAGS_REMOVE_vgettimeofday.o = $(CC_FLAGS_FTRACE) -Os $(CC_FLAGS_SCS) $(GCC_PLUGINS_CFLAGS) \
>                                 $(CC_FLAGS_LTO)
>  KASAN_SANITIZE                 := n
> +KCSAN_SANITIZE                 := n
>  UBSAN_SANITIZE                 := n
>  OBJECT_FILES_NON_STANDARD      := y
>  KCOV_INSTRUMENT                        := n
> diff --git a/arch/arm64/kvm/hyp/nvhe/Makefile b/arch/arm64/kvm/hyp/nvhe/Makefile
> index c3c11974fa3b..24b2c2425b38 100644
> --- a/arch/arm64/kvm/hyp/nvhe/Makefile
> +++ b/arch/arm64/kvm/hyp/nvhe/Makefile
> @@ -89,6 +89,7 @@ KBUILD_CFLAGS := $(filter-out $(CC_FLAGS_FTRACE) $(CC_FLAGS_SCS) $(CC_FLAGS_CFI)
>  # cause crashes. Just disable it.
>  GCOV_PROFILE   := n
>  KASAN_SANITIZE := n
> +KCSAN_SANITIZE := n
>  UBSAN_SANITIZE := n
>  KCOV_INSTRUMENT        := n
>
> diff --git a/kernel/kcsan/Makefile b/kernel/kcsan/Makefile
> index c2bb07f5bcc7..e893b0e1d62a 100644
> --- a/kernel/kcsan/Makefile
> +++ b/kernel/kcsan/Makefile
> @@ -8,6 +8,7 @@ CFLAGS_REMOVE_debugfs.o = $(CC_FLAGS_FTRACE)
>  CFLAGS_REMOVE_report.o = $(CC_FLAGS_FTRACE)
>
>  CFLAGS_core.o := $(call cc-option,-fno-conserve-stack) \
> +       $(call cc-option,-mno-outline-atomics) \
>         -fno-stack-protector -DDISABLE_BRANCH_PROFILING
>
>  obj-y := core.o debugfs.o report.o
> --
> 2.26.2
>