Skip to contentSkip to conversation

kasan: Disable branch tracing for core runtime

PATCH Applied Marco Elver 2 participants 3 messages May 22, 2020 – May 23, 2020

Subsystems (2)
Memory management KASAN
lore
Share & tools
lore

Marco Elver

author
#0 lore raw

PATCH v2 1/1 kasan: Disable branch tracing for core runtime

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/ open here
Reported-by kernel test robot <[email protected]>
Signed-off-by Marco Elver <[email protected]>

---
v2:
* Remove duplicate DISABLE_BRANCH_PROFILING from tags.c as reported by Qian Cai.

---
 mm/kasan/Makefile  | 16 ++++++++--------
 mm/kasan/generic.c |  1 -
 mm/kasan/tags.c    |  1 -
 3 files changed, 8 insertions(+), 10 deletions(-)
mm/kasan/Makefile +8 -8
index 434d503a6525..de3121848ddf 100644
@@ -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
mm/kasan/generic.c +0 -1
index 56ff8885fe2e..098a7dbaced6 100644
@@ -15,7 +15,6 @@
  */
 
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
-#define DISABLE_BRANCH_PROFILING
 
 #include <linux/export.h>
 #include <linux/interrupt.h>
mm/kasan/tags.c +0 -1
index 25b7734e7013..8a959fdd30e3 100644
@@ -12,7 +12,6 @@
  */
 
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
-#define DISABLE_BRANCH_PROFILING
 
 #include <linux/export.h>
 #include <linux/interrupt.h>
Signature · 1 line
2.27.0.rc0.183.gde8f92d652-goog
maintainer
#1 lore raw
Quoted 7 lines · On Fri, 22 May 2020 09:52:07 +0200 Marco Elver <[email protected]> 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.

Quoted 6 lines

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/ open here
Reported-by kernel test robot <[email protected]>
Signed-off-by Marco Elver <[email protected]>

I assume this affects 5.6 and perhaps earlier kernels?

I also assume that a cc:stable is appropriate for this fix?

author
#2 lore raw
Quoted 13 lines · Andrew Morton
Quoted 10 lines · On Fri, 22 May 2020 09:52:07 +0200 Marco Elver <[email protected]> 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.

Quoted 7 lines
Quoted 3 lines
Link https://lore.kernel.org/lkml/20200517011732.GE24705@shao2-debian/ open here
Reported-by kernel test robot <[email protected]>
Signed-off-by Marco Elver <[email protected]>

I assume this affects 5.6 and perhaps earlier kernels?

I also assume that a cc:stable is appropriate for this fix?

Yes, it does. On the other hand, the workaround is simple enough (disable any kind of branch profiling).

Note, the patch won't cleanly apply to 5.6 and early without this:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=8a16c09edc58982d56c49ab577fdcdf830fbc3a5

Thanks,
-- Marco