Re: [PATCH] kasan: Disable branch tracing for core runtime

[Marco Elver <elver@google.com>]

On Fri, 22 May 2020 at 00:11, Qian Cai <cai@lca.pw> wrote:
>
> On Tue, May 19, 2020 at 08:24:59PM +0200, 'Marco Elver' via kasan-dev 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)
>
> mm/kasan/tags.c:15:9: warning: 'DISABLE_BRANCH_PROFILING' macro redefined [-Wmacro-redefined]
> #define DISABLE_BRANCH_PROFILING
>         ^
> <command line>:6:9: note: previous definition is here
> #define DISABLE_BRANCH_PROFILING 1
>         ^
>
> This?
>
> diff --git a/mm/kasan/tags.c b/mm/kasan/tags.c
> index 25b7734e7013..8a959fdd30e3 100644
> --- a/mm/kasan/tags.c
> +++ b/mm/kasan/tags.c
> @@ -12,7 +12,6 @@
>   */
>
>  #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
> -#define DISABLE_BRANCH_PROFILING
>
>  #include <linux/export.h>
>  #include <linux/interrupt.h>
>

I missed this one, thanks! Added this to v2.

v2: https://lkml.kernel.org/r/20200522075207.157349-1-elver@google.com