[PATCH 5.6 109/126] kasan: disable branch tracing for core runtime

[Greg Kroah-Hartman]

From: Marco Elver <elver@xxxxxxxxxx>

commit 33cd65e73abd693c00c4156cf23677c453b41b3b upstream.

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.

[elver@xxxxxxxxxx: remove duplicate DISABLE_BRANCH_PROFILING, per Qian Cai]
  Link: https://lore.kernel.org/lkml/20200517011732.GE24705@shao2-debian/
  Link: http://lkml.kernel.org/r/20200522075207.157349-1-elver@xxxxxxxxxx
Reported-by: kernel test robot <rong.a.chen@xxxxxxxxx>
Signed-off-by: Marco Elver <elver@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Reviewed-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Cc: Alexander Potapenko <glider@xxxxxxxxxx>
Cc: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
Cc: Qian Cai <cai@xxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r//20200517011732.GE24705@shao2-debian/
Link: http://lkml.kernel.org/r/20200519182459.87166-1-elver@xxxxxxxxxx
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 mm/kasan/Makefile  |    8 ++++----
 mm/kasan/generic.c |    1 -
 mm/kasan/tags.c    |    1 -
 3 files changed, 4 insertions(+), 6 deletions(-)

--- a/mm/kasan/Makefile
+++ b/mm/kasan/Makefile
@@ -14,10 +14,10 @@ CFLAGS_REMOVE_tags.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_tags.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_tags.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
--- 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>
--- 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>