Merge "mm, memcg: fix potential undefined behaviour in page stat accounting"

Undefined Behavior Sanitizer - UBSAN

Overview

--------

UBSAN is a runtime undefined behaviour checker.

UBSAN uses compile-time instrumentation to catch undefined behavior (UB).

Compiler inserts code that perform certain kinds of checks before operations

that may cause UB. If check fails (i.e. UB detected) __ubsan_handle_*

function called to print error message.

GCC has that feature since 4.9.x [1] (see -fsanitize=undefined option and

its suboptions). GCC 5.x has more checkers implemented [2].

Report example

---------------

	 ================================================================================

	 UBSAN: Undefined behaviour in ../include/linux/bitops.h:110:33

	 shift exponent 32 is to large for 32-bit type 'unsigned int'

	 CPU: 0 PID: 0 Comm: swapper Not tainted 4.4.0-rc1+ #26

	  0000000000000000 ffffffff82403cc8 ffffffff815e6cd6 0000000000000001

	  ffffffff82403cf8 ffffffff82403ce0 ffffffff8163a5ed 0000000000000020

	  ffffffff82403d78 ffffffff8163ac2b ffffffff815f0001 0000000000000002

	 Call Trace:

	  [<ffffffff815e6cd6>] dump_stack+0x45/0x5f

	  [<ffffffff8163a5ed>] ubsan_epilogue+0xd/0x40

	  [<ffffffff8163ac2b>] __ubsan_handle_shift_out_of_bounds+0xeb/0x130

	  [<ffffffff815f0001>] ? radix_tree_gang_lookup_slot+0x51/0x150

	  [<ffffffff8173c586>] _mix_pool_bytes+0x1e6/0x480

	  [<ffffffff83105653>] ? dmi_walk_early+0x48/0x5c

	  [<ffffffff8173c881>] add_device_randomness+0x61/0x130

	  [<ffffffff83105b35>] ? dmi_save_one_device+0xaa/0xaa

	  [<ffffffff83105653>] dmi_walk_early+0x48/0x5c

	  [<ffffffff831066ae>] dmi_scan_machine+0x278/0x4b4

	  [<ffffffff8111d58a>] ? vprintk_default+0x1a/0x20

	  [<ffffffff830ad120>] ? early_idt_handler_array+0x120/0x120

	  [<ffffffff830b2240>] setup_arch+0x405/0xc2c

	  [<ffffffff830ad120>] ? early_idt_handler_array+0x120/0x120

	  [<ffffffff830ae053>] start_kernel+0x83/0x49a

	  [<ffffffff830ad120>] ? early_idt_handler_array+0x120/0x120

	  [<ffffffff830ad386>] x86_64_start_reservations+0x2a/0x2c

	  [<ffffffff830ad4f3>] x86_64_start_kernel+0x16b/0x17a

	 ================================================================================

Usage

-----

To enable UBSAN configure kernel with:

	CONFIG_UBSAN=y

and to check the entire kernel:

        CONFIG_UBSAN_SANITIZE_ALL=y

To enable instrumentation for specific files or directories, add a line

similar to the following to the respective kernel Makefile:

        For a single file (e.g. main.o):

                UBSAN_SANITIZE_main.o := y

        For all files in one directory:

                UBSAN_SANITIZE := y

To exclude files from being instrumented even if

CONFIG_UBSAN_SANITIZE_ALL=y, use:

                UBSAN_SANITIZE_main.o := n

        and:

                UBSAN_SANITIZE := n

Detection of unaligned accesses controlled through the separate option -

CONFIG_UBSAN_ALIGNMENT. It's off by default on architectures that support

unaligned accesses (CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS=y). One could

still enable it in config, just note that it will produce a lot of UBSAN

reports.

References

----------

[1] - https://gcc.gnu.org/onlinedocs/gcc-4.9.0/gcc/Debugging-Options.html

[2] - https://gcc.gnu.org/onlinedocs/gcc/Debugging-Options.html

export HOSTCXX HOSTCXXFLAGS LDFLAGS_MODULE CHECK CHECKFLAGS

export KBUILD_CPPFLAGS NOSTDINC_FLAGS LINUXINCLUDE OBJCOPYFLAGS LDFLAGS

export KBUILD_CFLAGS CFLAGS_KERNEL CFLAGS_MODULE CFLAGS_GCOV CFLAGS_KASAN

export KBUILD_CFLAGS CFLAGS_KERNEL CFLAGS_MODULE CFLAGS_GCOV CFLAGS_KASAN CFLAGS_UBSAN

export KBUILD_AFLAGS AFLAGS_KERNEL AFLAGS_MODULE

export KBUILD_AFLAGS_MODULE KBUILD_CFLAGS_MODULE KBUILD_LDFLAGS_MODULE

export KBUILD_AFLAGS_KERNEL KBUILD_CFLAGS_KERNEL

include $(srctree)/scripts/Makefile.kasan

include $(srctree)/scripts/Makefile.extrawarn

include $(srctree)/scripts/Makefile.ubsan

# Add user supplied CPPFLAGS, AFLAGS and CFLAGS as the last assignments

KBUILD_CPPFLAGS += $(KCPPFLAGS)

	select ARCH_MIGHT_HAVE_ACPI_PDC if ACPI

	select ARCH_HAS_DEBUG_STRICT_USER_COPY_CHECKS

	select ARCH_HAS_FAST_MULTIPLIER

	select ARCH_HAS_UBSAN_SANITIZE_ALL

	select ARCH_MIGHT_HAVE_PC_PARPORT

	select ARCH_MIGHT_HAVE_PC_SERIO

	select HAVE_AOUT if X86_32

KBUILD_CFLAGS	:= $(USERINCLUDE) $(REALMODE_CFLAGS) -D_SETUP

KBUILD_AFLAGS	:= $(KBUILD_CFLAGS) -D__ASSEMBLY__

GCOV_PROFILE := n

UBSAN_SANITIZE := n

$(obj)/bzImage: asflags-y  := $(SVGA_MODE)

KBUILD_AFLAGS  := $(KBUILD_CFLAGS) -D__ASSEMBLY__

GCOV_PROFILE := n

UBSAN_SANITIZE :=n

LDFLAGS := -m elf_$(UTS_MACHINE)

LDFLAGS_vmlinux := -T