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

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Date:   Thu, 21 May 2020 18:11:33 -0400
From:   Qian Cai <cai@....pw>
To:     Marco Elver <elver@...gle.com>
Cc:     dvyukov@...gle.com, glider@...gle.com, andreyknvl@...gle.com,
        linux-kernel@...r.kernel.org, kasan-dev@...glegroups.com,
        aryabinin@...tuozzo.com, akpm@...ux-foundation.org,
        linux-mm@...ck.org, kernel test robot <rong.a.chen@...el.com>
Subject: Re: [PATCH] kasan: Disable branch tracing for core runtime

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@...el.com>
> Signed-off-by: Marco Elver <elver@...gle.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>