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From:   Andrey Konovalov <andreyknvl@google.com>
Date:   Tue, 19 May 2020 23:05:46 +0200
Message-ID: <CAAeHK+wcrmo=Hhwvqzd8kC-=5UR+fzRcA_4mo8wccWCTdrEzEQ@mail.gmail.com>
Subject: Re: [PATCH] kasan: Disable branch tracing for core runtime
To:     Marco Elver <elver@google.com>
Cc:     Dmitry Vyukov <dvyukov@google.com>,
        Alexander Potapenko <glider@google.com>,
        LKML <linux-kernel@vger.kernel.org>,
        kasan-dev <kasan-dev@googlegroups.com>,
        Andrey Ryabinin <aryabinin@virtuozzo.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linux Memory Management List <linux-mm@kvack.org>,
        kernel test robot <rong.a.chen@intel.com>
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On Tue, May 19, 2020 at 8:25 PM Marco Elver <elver@google.com> wrote:
>
> During early boot, while KASAN is not yet initialized, it is possible to
> enter reporting code-path and end up in kasan_report(). While
> uninitialized, the branch there prevents generating any reports,
> however, under certain circumstances when branches are being traced
> (TRACE_BRANCH_PROFILING), we may recurse deep enough to cause kernel
> reboots without warning.
>
> To prevent similar issues in future, we should disable branch tracing
> for the core runtime.
>
> Link: https://lore.kernel.org/lkml/20200517011732.GE24705@shao2-debian/
> Reported-by: kernel test robot <rong.a.chen@intel.com>
> Signed-off-by: Marco Elver <elver@google.com>
> ---
>  mm/kasan/Makefile  | 16 ++++++++--------
>  mm/kasan/generic.c |  1 -
>  2 files changed, 8 insertions(+), 9 deletions(-)
>
> diff --git a/mm/kasan/Makefile b/mm/kasan/Makefile
> index 434d503a6525..de3121848ddf 100644
> --- a/mm/kasan/Makefile
> +++ b/mm/kasan/Makefile
> @@ -15,14 +15,14 @@ CFLAGS_REMOVE_tags_report.o = $(CC_FLAGS_FTRACE)
>
>  # Function splitter causes unnecessary splits in __asan_load1/__asan_store1
>  # see: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63533
> -CFLAGS_common.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector)
> -CFLAGS_generic.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector)
> -CFLAGS_generic_report.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector)
> -CFLAGS_init.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector)
> -CFLAGS_quarantine.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector)
> -CFLAGS_report.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector)
> -CFLAGS_tags.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector)
> -CFLAGS_tags_report.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector)
> +CFLAGS_common.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector) -DDISABLE_BRANCH_PROFILING
> +CFLAGS_generic.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector) -DDISABLE_BRANCH_PROFILING
> +CFLAGS_generic_report.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector) -DDISABLE_BRANCH_PROFILING
> +CFLAGS_init.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector) -DDISABLE_BRANCH_PROFILING
> +CFLAGS_quarantine.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector) -DDISABLE_BRANCH_PROFILING
> +CFLAGS_report.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector) -DDISABLE_BRANCH_PROFILING
> +CFLAGS_tags.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector) -DDISABLE_BRANCH_PROFILING
> +CFLAGS_tags_report.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector) -DDISABLE_BRANCH_PROFILING
>
>  obj-$(CONFIG_KASAN) := common.o init.o report.o
>  obj-$(CONFIG_KASAN_GENERIC) += generic.o generic_report.o quarantine.o
> diff --git a/mm/kasan/generic.c b/mm/kasan/generic.c
> index 56ff8885fe2e..098a7dbaced6 100644
> --- a/mm/kasan/generic.c
> +++ b/mm/kasan/generic.c
> @@ -15,7 +15,6 @@
>   */
>
>  #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
> -#define DISABLE_BRANCH_PROFILING
>
>  #include <linux/export.h>
>  #include <linux/interrupt.h>
> --
> 2.26.2.761.g0e0b3e54be-goog
>

Reviewed-by: Andrey Konovalov <andreyknvl@google.com>

Thanks!