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Commit c6d30853 authored by Andrey Ryabinin's avatar Andrey Ryabinin Committed by Linus Torvalds
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UBSAN: run-time undefined behavior sanity checker 

UBSAN uses compile-time instrumentation to catch undefined behavior
(UB).  Compiler inserts code that perform certain kinds of checks before
operations that could cause UB.  If check fails (i.e.  UB detected)
__ubsan_handle_* function called to print error message.

So the most of the work is done by compiler.  This patch just implements
ubsan handlers printing errors.

GCC has this capability since 4.9.x [1] (see -fsanitize=undefined
option and its suboptions).
However GCC 5.x has more checkers implemented [2].
Article [3] has a bit more details about UBSAN in the GCC.

[1] - https://gcc.gnu.org/onlinedocs/gcc-4.9.0/gcc/Debugging-Options.html
[2] - https://gcc.gnu.org/onlinedocs/gcc/Debugging-Options.html
[3] - http://developerblog.redhat.com/2014/10/16/gcc-undefined-behavior-sanitizer-ubsan/

Issues which UBSAN has found thus far are:

Found bugs:

 * out-of-bounds access - 97840cb6 ("netfilter: nfnetlink: fix
   insufficient validation in nfnetlink_bind")

undefined shifts:

 * d48458d4 ("jbd2: use a better hash function for the revoke
   table")

 * 10632008 ("clockevents: Prevent shift out of bounds")

 * 'x << -1' shift in ext4 -
   http://lkml.kernel.org/r/<5444EF21.8020501@samsung.com>

 * undefined rol32(0) -
   http://lkml.kernel.org/r/<1449198241-20654-1-git-send-email-sasha.levin@oracle.com>

 * undefined dirty_ratelimit calculation -
   http://lkml.kernel.org/r/<566594E2.3050306@odin.com>

 * undefined roundown_pow_of_two(0) -
   http://lkml.kernel.org/r/<1449156616-11474-1-git-send-email-sasha.levin@oracle.com>

 * [WONTFIX] undefined shift in __bpf_prog_run -
   http://lkml.kernel.org/r/<CACT4Y+ZxoR3UjLgcNdUm4fECLMx2VdtfrENMtRRCdgHB2n0bJA@mail.gmail.com>

   WONTFIX here because it should be fixed in bpf program, not in kernel.

signed overflows:

 * 32a8df4e ("sched: Fix odd values in effective_load()
   calculations")

 * mul overflow in ntp -
   http://lkml.kernel.org/r/<1449175608-1146-1-git-send-email-sasha.levin@oracle.com>

 * incorrect conversion into rtc_time in rtc_time64_to_tm() -
   http://lkml.kernel.org/r/<1449187944-11730-1-git-send-email-sasha.levin@oracle.com>

 * unvalidated timespec in io_getevents() -
   http://lkml.kernel.org/r/<CACT4Y+bBxVYLQ6LtOKrKtnLthqLHcw-BMp3aqP3mjdAvr9FULQ@mail.gmail.com>

 * [NOTABUG] signed overflow in ktime_add_safe() -
   http://lkml.kernel.org/r/<CACT4Y+aJ4muRnWxsUe1CMnA6P8nooO33kwG-c8YZg=0Xc8rJqw@mail.gmail.com

>

[akpm@linux-foundation.org: fix unused local warning]
[akpm@linux-foundation.org: fix __int128 build woes]
Signed-off-by: default avatarAndrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sasha Levin <sasha.levin@oracle.com>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Michal Marek <mmarek@suse.cz>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Yury Gribov <y.gribov@samsung.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Konstantin Khlebnikov <koct9i@gmail.com>
Cc: Kostya Serebryany <kcc@google.com>
Cc: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 68920c97

Documentation/ubsan.txt

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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

Makefile

+2 −1
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@@ -411,7 +411,7 @@ export MAKE AWK GENKSYMS INSTALLKERNEL PERL PYTHON UTS_MACHINE 
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
@@ -784,6 +784,7 @@ endif 


include scripts/Makefile.kasan

include scripts/Makefile.extrawarn

include scripts/Makefile.ubsan



# Add any arch overrides and user supplied CPPFLAGS, AFLAGS and CFLAGS as the

# last assignments

arch/x86/Kconfig

+1 −0
Original line number Diff line number Diff line
@@ -31,6 +31,7 @@ config X86 
	select ARCH_HAS_PMEM_API		if X86_64

	select ARCH_HAS_MMIO_FLUSH

	select ARCH_HAS_SG_CHAIN

	select ARCH_HAS_UBSAN_SANITIZE_ALL

	select ARCH_HAVE_NMI_SAFE_CMPXCHG

	select ARCH_MIGHT_HAVE_ACPI_PDC		if ACPI

	select ARCH_MIGHT_HAVE_PC_PARPORT

arch/x86/boot/Makefile

+1 −0
Original line number Diff line number Diff line
@@ -60,6 +60,7 @@ clean-files += cpustr.h 
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)

arch/x86/boot/compressed/Makefile

+1 −0
Original line number Diff line number Diff line
@@ -33,6 +33,7 @@ KBUILD_CFLAGS += $(call cc-option,-fno-stack-protector) 


KBUILD_AFLAGS  := $(KBUILD_CFLAGS) -D__ASSEMBLY__

GCOV_PROFILE := n

UBSAN_SANITIZE :=n



LDFLAGS := -m elf_$(UTS_MACHINE)

LDFLAGS_vmlinux := -T