This test is userspace code, but uses some kernel headers via symlinks,
and mocks other headers, in order to test load_unaligned_zeropad().

Currently the test fails to build with:

  In file included from load_unaligned_zeropad.c:26:
  word-at-a-time.h:7:10: fatal error: linux/bitops.h: No such file or directory
      7 | #include <linux/bitops.h>

This is due to the recent changes to the kernel headers.

Fix it by symlinking the new wordpart.h, and creating an empty stub for
bitops.h which is all that's needed.
Reported-by: Sachin Sant <sachinp@linux.ibm.com>
Tested-by: Sachin Sant <sachinp@linux.ibm.com>
Fixes: 66a5c40f ("kernel.h: removed REPEAT_BYTE from kernel.h")
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20240305125644.3315910-1-mpe@ellerman.id.auSigned-off-by: Kees Cook <keescook@chromium.org>

Convert test-string_helpers.c to KUnit so it can be easily run with
everything else.

Failure reporting doesn't need to be open-coded in most places, for
example, forcing a failure in the expected output for upper/lower
testing looks like this:

[12:18:43] # test_upper_lower: EXPECTATION FAILED at lib/string_helpers_kunit.c:579
[12:18:43] Expected dst == strings_upper[i].out, but
[12:18:43]     dst == "ABCDEFGH1234567890TEST"
[12:18:43]     strings_upper[i].out == "ABCDEFGH1234567890TeST"
[12:18:43] [FAILED] test_upper_lower

Currently passes without problems:

$ ./tools/testing/kunit/kunit.py run string_helpers
...
[12:23:55] Starting KUnit Kernel (1/1)...
[12:23:55] ============================================================
[12:23:55] =============== string_helpers (3 subtests) ================
[12:23:55] [PASSED] test_get_size
[12:23:55] [PASSED] test_upper_lower
[12:23:55] [PASSED] test_unescape
[12:23:55] ================= [PASSED] string_helpers ==================
[12:23:55] ============================================================
[12:23:55] Testing complete. Ran 3 tests: passed: 3
[12:23:55] Elapsed time: 6.709s total, 0.001s configuring, 6.591s building, 0.066s running

Link: https://lore.kernel.org/r/20240301202732.2688342-2-keescook@chromium.orgSigned-off-by: Kees Cook <keescook@chromium.org>

Convert test_string.c to KUnit so it can be easily run with everything
else.

Additional text context is retained for failure reporting. For example,
when forcing a bad match, we can see the loop counters reported for the
memset() tests:

[09:21:52]     # test_memset64: ASSERTION FAILED at lib/string_kunit.c:93
[09:21:52]     Expected v == 0xa2a1a1a1a1a1a1a1ULL, but
[09:21:52]         v == -6799976246779207263 (0xa1a1a1a1a1a1a1a1)
[09:21:52]         0xa2a1a1a1a1a1a1a1ULL == -6727918652741279327 (0xa2a1a1a1a1a1a1a1)
[09:21:52] i:0 j:0 k:0
[09:21:52] [FAILED] test_memset64

Currently passes without problems:

$ ./tools/testing/kunit/kunit.py run string
...
[09:37:40] Starting KUnit Kernel (1/1)...
[09:37:40] ============================================================
[09:37:40] =================== string (6 subtests) ====================
[09:37:40] [PASSED] test_memset16
[09:37:40] [PASSED] test_memset32
[09:37:40] [PASSED] test_memset64
[09:37:40] [PASSED] test_strchr
[09:37:40] [PASSED] test_strnchr
[09:37:40] [PASSED] test_strspn
[09:37:40] ===================== [PASSED] string ======================
[09:37:40] ============================================================
[09:37:40] Testing complete. Ran 6 tests: passed: 6
[09:37:40] Elapsed time: 6.730s total, 0.001s configuring, 6.562s building, 0.131s running

Link: https://lore.kernel.org/r/20240301202732.2688342-1-keescook@chromium.orgSigned-off-by: Kees Cook <keescook@chromium.org>

The early boot stub for sh had UBSan instrumentation present where it is
not supported. Disable it for this part of the build.

  sh4-linux-ld: arch/sh/boot/compressed/misc.o: in function `zlib_inflate_table':
  misc.c:(.text+0x670): undefined reference to `__ubsan_handle_shift_out_of_bounds'
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202401310416.s8HLiLnC-lkp@intel.com/
Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
Cc: Rich Felker <dalias@libc.org>
Cc: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
Cc: Masahiro Yamada <masahiroy@kernel.org>
Cc: Nicolas Schier <n.schier@avm.de>
Cc:  <linux-sh@vger.kernel.org>
Link: https://lore.kernel.org/r/20240130232717.work.088-kees@kernel.orgSigned-off-by: Kees Cook <keescook@chromium.org>

The __is_constexpr() macro is dark magic. Shed some light on it with
a comment to explain how and why it works.
Acked-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Link: https://lore.kernel.org/r/20240301044428.work.411-kees@kernel.orgSigned-off-by: Kees Cook <keescook@chromium.org>

A common use of type_max() is to find the max for the type of a
variable. Using the pattern type_max(typeof(var)) is needlessly
verbose. Instead, since typeof(type) == type we can just explicitly
call typeof() on the argument to type_max() and type_min(). Add
wrappers for readability.

We can do some replacements right away:

$ git grep '\btype_\(min\|max\)(typeof' | wc -l
11

Link: https://lore.kernel.org/r/20240301062221.work.840-kees@kernel.orgSigned-off-by: Kees Cook <keescook@chromium.org>

The changes are similar to those given in the commit 19b070fe
("VMCI: Fix memcpy() run-time warning in dg_dispatch_as_host()").

Fix filling of the msg and msg_payload in dg_info struct, which prevents a
possible "detected field-spanning write" of memcpy warning that is issued
by the tracking mechanism __fortify_memcpy_chk.
Signed-off-by: Vasiliy Kovalev <kovalev@altlinux.org>
Link: https://lore.kernel.org/r/20240219105315.76955-1-kovalev@altlinux.orgSigned-off-by: Kees Cook <keescook@chromium.org>

The new flags parameter allows controlling
 - Whether or not the units suffix is separated by a space, for
   compatibility with sort -h
 - Whether or not to append a B suffix - we're not always printing
   bytes.
Co-developed-by: Kent Overstreet <kent.overstreet@linux.dev>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Kent Overstreet <kent.overstreet@linux.dev>
Link: https://lore.kernel.org/r/20240229205345.93902-1-andriy.shevchenko@linux.intel.comSigned-off-by: Kees Cook <keescook@chromium.org>

When building with CONFIG_XEN_PV=y, .text symbols are emitted into
the .notes section so that Xen can find the "startup_xen" entry point.
This information is used prior to booting the kernel, so relocations
are not useful. In fact, performing relocations against the .notes
section means that the KASLR base is exposed since /sys/kernel/notes
is world-readable.

To avoid leaking the KASLR base without breaking unprivileged tools that
are expecting to read /sys/kernel/notes, skip performing relocations in
the .notes section. The values readable in .notes are then identical to
those found in System.map.
Reported-by: Guixiong Wei <guixiongwei@gmail.com>
Closes: https://lore.kernel.org/all/20240218073501.54555-1-guixiongwei@gmail.com/
Fixes: 5ead97c8 ("xen: Core Xen implementation")
Fixes: da1a679c ("Add /sys/kernel/notes")
Reviewed-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Kees Cook <keescook@chromium.org>

If SAVE and RESTORE unwind hints are in different basic blocks, and
objtool sees the RESTORE before the SAVE, it errors out with:

  vmlinux.o: warning: objtool: vmw_port_hb_in+0x242: objtool isn't smart enough to handle this CFI save/restore combo

In such a case, defer following the RESTORE block until the
straight-line path gets followed later.

Fixes: 8faea26e ("objtool: Re-add UNWIND_HINT_{SAVE_RESTORE}")
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202402240702.zJFNmahW-lkp@intel.com/Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Link: https://lore.kernel.org/r/20240227073527.avcm5naavbv3cj5s@trebleSigned-off-by: Kees Cook <keescook@chromium.org>

The check_shl_overflow() uses u64 type that is defined in types.h.
Instead of including that header, just switch to use POD type
directly.
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20240228204919.3680786-2-andriy.shevchenko@linux.intel.comSigned-off-by: Kees Cook <keescook@chromium.org>

For reasons I cannot understand, m68k moves the start of the stack frame
for consecutive calls to the same function if the function's test
variable is larger than 8 bytes. This was only happening for the char
array test (obviously), so adjust the length of the string for m68k
only. I want the array size to be longer than "unsigned long" for every
given architecture, so the other remain unchanged.

Additionally adjust the error message to be a bit more clear about
what's happened, and move the KUNIT check outside of the consecutive
calls to minimize what happens between them.
Reported-by: Guenter Roeck <linux@roeck-us.net>
Closes: https://lore.kernel.org/lkml/a0d10d50-2720-4ecd-a2c6-c2c5e5aeee65@roeck-us.net/Tested-by: Guenter Roeck <linux@roeck-us.net>
Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
Closes: https://lore.kernel.org/r/CAMuHMdX_g1tbiUL9PUQdqaegrEzCNN3GtbSvSBFYAL4TzvstFg@mail.gmail.com
Closes: https://lore.kernel.org/r/CAMuHMdW6N40+0gGQ+LSrN64Mo4A0-ELAm0pR3gWQ0mNanyBuUQ@mail.gmail.comTested-by: Geert Uytterhoeven <geert@linux-m68k.org>
Link: https://lore.kernel.org/all/a4bf4063-194f-4740-9c1d-88f9ab38b778@roeck-us.netSigned-off-by: Kees Cook <keescook@chromium.org>

The UBSAN instrumentation cannot work in the vDSO since it is executing
in userspace, so disable it in the Makefile. Fixes the build failures
such as:

arch/sparc/vdso/vclock_gettime.c:217: undefined reference to `__ubsan_handle_shift_out_of_bounds'
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://lore.kernel.org/all/20240224073617.GA2959352@ravnborg.orgSigned-off-by: Kees Cook <keescook@chromium.org>

The lib/cmdline.c is basically a set of some small string parsers
which are wide used in the kernel. Their prototypes belong to the
string.h rather then kernel.h.
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20231003130142.2936503-1-andriy.shevchenko@linux.intel.comSigned-off-by: Kees Cook <keescook@chromium.org>

Introduce --kallsyms argument for scanning binary files for known symbol
addresses. This would have found the exposure in /sys/kernel/notes:

$ scripts/leaking_addresses.pl --kallsyms=<(sudo cat /proc/kallsyms)
/sys/kernel/notes: hypercall_page @ 156
/sys/kernel/notes: xen_hypercall_set_trap_table @ 156
/sys/kernel/notes: startup_xen @ 132
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Tycho Andersen <tandersen@netflix.com>
Link: https://lore.kernel.org/r/20240222220053.1475824-4-keescook@chromium.orgSigned-off-by: Kees Cook <keescook@chromium.org>

These are false positives from the input subsystem:

/proc/bus/input/devices: B: KEY=402000000 3803078f800d001 feffffdfffefffff fffffffffffffffe
/sys/devices/platform/i8042/serio0/input/input1/uevent: KEY=402000000 3803078f800d001 feffffdfffefffff fffffffffffffffe
/sys/devices/platform/i8042/serio0/input/input1/capabilities/key: 402000000 3803078f800d001 feffffdf

Pass in the filename for more context and expand the "ignored pattern"
matcher to notice these.
Reviewed-by: Tycho Andersen <tandersen@netflix.com>
Link: https://lore.kernel.org/r/20240222220053.1475824-3-keescook@chromium.orgSigned-off-by: Kees Cook <keescook@chromium.org>

Instead of using a statically named path in /tmp, use File::Temp to create
(and remove) the temporary file used for parsing /proc/config.gz.
Reviewed-by: Tycho Andersen <tandersen@netflix.com>
Link: https://lore.kernel.org/r/20240222220053.1475824-2-keescook@chromium.orgSigned-off-by: Kees Cook <keescook@chromium.org>

Tobin hasn't been involved lately, and I can step up to be a reviewer
with Tycho. I'll carry changes via the hardening tree.
Reviewed-by: Tycho Andersen <tandersen@netflix.com>
Link: https://lore.kernel.org/r/20240222220053.1475824-1-keescook@chromium.orgSigned-off-by: Kees Cook <keescook@chromium.org>

Improve the reporting of buffer overflows under CONFIG_FORTIFY_SOURCE to
help accelerate debugging efforts. The calculations are all just sitting
in registers anyway, so pass them along to the function to be reported.

For example, before:

  detected buffer overflow in memcpy

and after:

  memcpy: detected buffer overflow: 4096 byte read of buffer size 1

Link: https://lore.kernel.org/r/20230407192717.636137-10-keescook@chromium.orgSigned-off-by: Kees Cook <keescook@chromium.org>

With fortify overflows able to be redirected, we can use KUnit to
exercise the overflow conditions. Add tests for every API covered by
CONFIG_FORTIFY_SOURCE, except for memset() and memcpy(), which are
special-cased for now.

Disable warnings in the Makefile since we're explicitly testing
known-bad string handling code patterns.

Note that this makes the LKDTM FORTIFY_STR* tests obsolete, but those
can be removed separately.
Signed-off-by: Kees Cook <keescook@chromium.org>

The standard C string APIs were not designed to have a failure mode;
they were expected to always succeed without memory safety issues.
Normally, CONFIG_FORTIFY_SOURCE will use fortify_panic() to stop
processing, as truncating a read or write may provide an even worse
system state. However, this creates a problem for testing under things
like KUnit, which needs a way to survive failures.

When building with CONFIG_KUNIT, provide a failure path for all users
of fortify_panic, and track whether the failure was a read overflow or
a write overflow, for KUnit tests to examine. Inspired by similar logic
in the slab tests.
Signed-off-by: Kees Cook <keescook@chromium.org>

In order for CI systems to notice all the skipped tests related to
CONFIG_FORTIFY_SOURCE, allow the FORTIFY_SOURCE KUnit tests to build
with or without CONFIG_FORTIFY_SOURCE.
Signed-off-by: Kees Cook <keescook@chromium.org>

In preparation for KUnit testing and further improvements in fortify
failure reporting, split out the report and encode the function and access
failure (read or write overflow) into a single u8 argument. This mainly
ends up saving a tiny bit of space in the data segment. For a defconfig
with FORTIFY_SOURCE enabled:

$ size gcc/vmlinux.before gcc/vmlinux.after
   text  	  data     bss     dec    	    hex filename
26132309        9760658 2195460 38088427        2452eeb gcc/vmlinux.before
26132386        9748382 2195460 38076228        244ff44 gcc/vmlinux.after
Reviewed-by: Alexander Lobakin <aleksander.lobakin@intel.com>
Signed-off-by: Kees Cook <keescook@chromium.org>

Mark the various refcount_t functions with __signed_wrap, as we depend
on the wrapping behavior to detect the overflow and perform saturation.
Silences warnings seen with the LKDTM REFCOUNT_* tests:

  UBSAN: signed-integer-overflow in ../include/linux/refcount.h:189:11
  2147483647 + 1 cannot be represented in type 'int'
Reviewed-by: Miguel Ojeda <ojeda@kernel.org>
Link: https://lore.kernel.org/r/20240221051634.work.287-kees@kernel.orgSigned-off-by: Kees Cook <keescook@chromium.org>

include/linux/overflow.h includes helper macros intended for calculating
sizes of allocations. These macros prevent accidental overflow by
saturating at SIZE_MAX.

In general when calculating such sizes use of the macros is preferred. Add
a semantic patch which can detect code patterns which can be replaced by
struct_size.

Note that I set the confidence to medium because this patch doesn't make an
attempt to ensure that the relevant array is actually a flexible array. The
struct_size macro does specifically require a flexible array. In many cases
the detected code could be refactored to a flexible array, but this is not
always possible (such as if there are multiple over-allocations).
Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Link: https://lore.kernel.org/r/20230227202428.3657443-1-jacob.e.keller@intel.comSigned-off-by: Kees Cook <keescook@chromium.org>

Add rules for finding places where str_plural() can be used. This
currently finds:
 54 files changed, 62 insertions(+), 61 deletions(-)
Co-developed-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Link: https://lore.kernel.org/all/fc1b25a8-6381-47c2-831c-ab6b8201a82b@intel.com/Signed-off-by: Kees Cook <keescook@chromium.org>

Add str_plural() helper to replace existing open implementations
used by many drivers and help improve future user facing messages.
Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Link: https://lore.kernel.org/r/20240214165015.1656-1-michal.wajdeczko@intel.comSigned-off-by: Kees Cook <keescook@chromium.org>

This allows replacements of the idioms "var += offset" and "var -=
offset" with the wrapping_assign_add() and wrapping_assign_sub() helpers
respectively. They will avoid wrap-around sanitizer instrumentation.

Add to the selftests to validate behavior and lack of side-effects.
Reviewed-by: Marco Elver <elver@google.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Kees Cook <keescook@chromium.org>

Provide helpers that will perform wrapping addition, subtraction, or
multiplication without tripping the arithmetic wrap-around sanitizers. The
first argument is the type under which the wrap-around should happen
with. In other words, these two calls will get very different results:

	wrapping_mul(int, 50, 50) == 2500
	wrapping_mul(u8,  50, 50) ==  196

Add to the selftests to validate behavior and lack of side-effects.
Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Reviewed-by: Marco Elver <elver@google.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Kees Cook <keescook@chromium.org>

The check_*_overflow() helpers will return results with potentially
wrapped-around values. These values have always been checked by the
selftests, so avoid the confusing language in the kern-doc. The idea of
"safe for use" was relative to the expectation of whether or not the
caller wants a wrapped value -- the calculation itself will always follow
arithmetic wrapping rules.
Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Kees Cook <keescook@chromium.org>

The wordpart.h header is collecting APIs related to the handling
parts of the word (usually in byte granularity). The upper_*_bits()
and lower_*_bits() are good candidates to be moved to there.

This helps to clean up header dependency hell with regard to kernel.h
as the latter gathers completely unrelated stuff together and slows
down compilation (especially when it's included into other header).
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20240214172752.3605073-1-andriy.shevchenko@linux.intel.comReviewed-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Kees Cook <keescook@chromium.org>

KFENCE is not a security mitigation mechanism (due to sampling), but has
the performance characteristics of unintrusive hardening techniques.
When used at scale, however, it improves overall security by allowing
kernel developers to detect heap memory-safety bugs cheaply.

Link: https://lkml.kernel.org/r/79B9A832-B3DE-4229-9D87-748B2CFB7D12@kernel.org
Cc: Matthieu Baerts <matttbe@kernel.org>
Cc: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Marco Elver <elver@google.com>
Link: https://lore.kernel.org/r/20240212130116.997627-1-elver@google.comSigned-off-by: Kees Cook <keescook@chromium.org>

Commit 94f8f319 ("drm: Remove Kconfig option for legacy support
(CONFIG_DRM_LEGACY)") removes the config DRM_LEGACY, but one reference to
that config is left in the hardening.config fragment.

As there is no drm legacy driver left, we do not need to recommend this
attack surface reduction anymore.

Drop this reference in hardening.config fragment.
Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Link: https://lore.kernel.org/r/20240208091045.9219-3-lukas.bulwahn@gmail.comSigned-off-by: Kees Cook <keescook@chromium.org>

Commit 7a628f818499 ("ubsan: Remove CONFIG_UBSAN_SANITIZE_ALL") removes the
config UBSAN_SANITIZE_ALL, but one reference to that config is left in the
hardening.config fragment.

Drop this reference in hardening.config fragment.

Note that CONFIG_UBSAN is still enabled in the hardening.config fragment,
so the functionality when using this fragment remains the same.
Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Link: https://lore.kernel.org/r/20240208091045.9219-2-lukas.bulwahn@gmail.comSigned-off-by: Kees Cook <keescook@chromium.org>

The ARCH=um build has its own idea about strscpy()'s definition. Adjust
the callers to remove the redundant sizeof() arguments ahead of treewide
changes, since it needs a manual adjustment for the newly named
sized_strscpy() export.

Cc: Richard Weinberger <richard@nod.at>
Cc: linux-um@lists.infradead.org
Signed-off-by: Kees Cook <keescook@chromium.org>

Similar to strscpy(), update strscpy_pad()'s 3rd argument to be
optional when the destination is a compile-time known size array.

Cc: Andy Shevchenko <andy@kernel.org>
Cc:  <linux-hardening@vger.kernel.org>
Reviewed-by: Justin Stitt <justinstitt@google.com>
Signed-off-by: Kees Cook <keescook@chromium.org>

Using sizeof(dst) for the "size" argument in strscpy() is the
overwhelmingly common case. Instead of requiring this everywhere, allow a
2-argument version to be used that will use the sizeof() internally. There
are other functions in the kernel with optional arguments[1], so this
isn't unprecedented, and improves readability. Update and relocate the
kern-doc for strscpy() too, and drop __HAVE_ARCH_STRSCPY as it is unused.

Adjust ARCH=um build to notice the changed export name, as it doesn't
do full header includes for the string helpers.

This could additionally let us save a few hundred lines of code:
 1177 files changed, 2455 insertions(+), 3026 deletions(-)
with a treewide cleanup using Coccinelle:

@needless_arg@
expression DST, SRC;
@@

        strscpy(DST, SRC
-, sizeof(DST)
        )

Link: https://elixir.bootlin.com/linux/v6.7/source/include/linux/pci.h#L1517 [1]
Reviewed-by: Justin Stitt <justinstitt@google.com>
Cc: Andy Shevchenko <andy@kernel.org>
Cc: linux-hardening@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>

In preparation for making strscpy_pad()'s 3rd argument optional, redefine
it as a macro. This also has the benefit of allowing greater FORITFY
introspection, as it couldn't see into the strscpy() nor the memset()
within strscpy_pad().

Cc: Andy Shevchenko <andy@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc:  <linux-hardening@vger.kernel.org>
Reviewed-by: Justin Stitt <justinstitt@google.com>
Signed-off-by: Kees Cook <keescook@chromium.org>

In order to mitigate unexpected signed wrap-around[1], bring back the
signed integer overflow sanitizer. It was removed in commit 6aaa31ae
("ubsan: remove overflow checks") because it was effectively a no-op
when combined with -fno-strict-overflow (which correctly changes signed
overflow from being "undefined" to being explicitly "wrap around").

Compilers are adjusting their sanitizers to trap wrap-around and to
detecting common code patterns that should not be instrumented
(e.g. "var + offset < var"). Prepare for this and explicitly rename
the option from "OVERFLOW" to "WRAP" to more accurately describe the
behavior.

To annotate intentional wrap-around arithmetic, the helpers
wrapping_add/sub/mul_wrap() can be used for individual statements. At
the function level, the __signed_wrap attribute can be used to mark an
entire function as expecting its signed arithmetic to wrap around. For a
single object file the Makefile can use "UBSAN_SIGNED_WRAP_target.o := n"
to mark it as wrapping, and for an entire directory, "UBSAN_SIGNED_WRAP :=
n" can be used.

Additionally keep these disabled under CONFIG_COMPILE_TEST for now.

Link: https://github.com/KSPP/linux/issues/26 [1]
Cc: Miguel Ojeda <ojeda@kernel.org>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Hao Luo <haoluo@google.com>
Reviewed-by: Marco Elver <elver@google.com>
Reviewed-by: Justin Stitt <justinstitt@google.com>
Signed-off-by: Kees Cook <keescook@chromium.org>

For simplicity in splitting out UBSan options into separate rules,
remove CONFIG_UBSAN_SANITIZE_ALL, effectively defaulting to "y", which
is how it is generally used anyway. (There are no ":= y" cases beyond
where a specific file is enabled when a top-level ":= n" is in effect.)

Cc: Andrey Konovalov <andreyknvl@gmail.com>
Cc: Marco Elver <elver@google.com>
Cc: linux-doc@vger.kernel.org
Cc: linux-kbuild@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>