random: vDSO: avoid call to memset() when zeroing reserved parameter

After a recent change in LLVM [1], builds with the random vDSO
implementation, such as PowerPC and RISC-V, fail when checking the

random: vDSO: avoid call to memset() when zeroing reserved parameter

After a recent change in LLVM [1], builds with the random vDSO
implementation, such as PowerPC and RISC-V, fail when checking the vDSO:

arch/powerpc/kernel/vdso/vdso32.so.dbg: dynamic relocations are not supported
arch/riscv/kernel/vdso/vdso.so.dbg: dynamic relocations are not supported

memset() is now generated when zeroing params->reserved for some builds
because LLVM has an optimization (now run in more instances) that can
recognize at compile time when it is assigning a static value to a
contiguous area of memory and turn that into a call to memset(). Both
clang and GCC assume memset() is always available [2].

Clang has an internal fiddly hook, -max-store-memset, which we can set
to a high number, to disable generating out of line memset calls [3].
Similarly, GCC has -finline-stringops=memset to do the same [4], should
this issue ever hit future version of GCC. While these options wouldn't
make sense for normal kernel code, it is fine for the extremely limited
and intentionally compact vDSO code.

Link: https://github.com/llvm/llvm-project/commit/90cebef1411617fc3eedd359bdf00cb44b1c2439 [1]
Link: https://gcc.gnu.org/onlinedocs/gcc-16.2.0/gcc/Standards.html#index-ffreestanding [2]
Link: https://github.com/llvm/llvm-project/commit/b28eeb28bea39148738dc375e8a97072a1907e64 [3]
Link: https://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html#index-finline-stringops [4]
Closes: https://github.com/ClangBuiltLinux/linux/issues/2183
Cc: stable@vger.kernel.org # v6.12+
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

show more ...

stackleak: Split KSTACK_ERASE_CFLAGS from GCC_PLUGINS_CFLAGS

In preparation for Clang stack depth tracking for KSTACK_ERASE,
split the stackleak-specific cflags out of GCC_PLUGINS_CFLAGS into
KSTACK

stackleak: Split KSTACK_ERASE_CFLAGS from GCC_PLUGINS_CFLAGS

In preparation for Clang stack depth tracking for KSTACK_ERASE,
split the stackleak-specific cflags out of GCC_PLUGINS_CFLAGS into
KSTACK_ERASE_CFLAGS.

Link: https://lore.kernel.org/r/20250717232519.2984886-3-kees@kernel.org
Signed-off-by: Kees Cook <kees@kernel.org>

show more ...

vdso: Rename included Makefile

As the Makefile is included into other Makefiles it can not be used to
define objects to be built from the current source directory.
However the generic datastore will

vdso: Rename included Makefile

As the Makefile is included into other Makefiles it can not be used to
define objects to be built from the current source directory.
However the generic datastore will introduce such a local source file.
Rename the included Makefile so it is clear how it is to be used and to
make room for a regular Makefile in lib/vdso/.

Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/20250204-vdso-store-rng-v3-4-13a4669dfc8c@linutronix.de

show more ...

arm64: vDSO: Wire up getrandom() vDSO implementation

Hook up the generic vDSO implementation to the aarch64 vDSO data page.
The _vdso_rng_data required data is placed within the _vdso_data vvar
page

arm64: vDSO: Wire up getrandom() vDSO implementation

Hook up the generic vDSO implementation to the aarch64 vDSO data page.
The _vdso_rng_data required data is placed within the _vdso_data vvar
page, by using a offset larger than the vdso_data.

The vDSO function requires a ChaCha20 implementation that does not write
to the stack, and that can do an entire ChaCha20 permutation. The one
provided uses NEON on the permute operation, with a fallback to the
syscall for chips that do not support AdvSIMD.

This also passes the vdso_test_chacha test along with
vdso_test_getrandom. The vdso_test_getrandom bench-single result on
Neoverse-N1 shows:

vdso: 25000000 times in 0.783884250 seconds
libc: 25000000 times in 8.780275399 seconds
syscall: 25000000 times in 8.786581518 seconds

A small fixup to arch/arm64/include/asm/mman.h was required to avoid
pulling kernel code into the vDSO, similar to what's already done in
arch/arm64/include/asm/rwonce.h.

Signed-off-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Acked-by: Will Deacon <will@kernel.org>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

show more ...

arm64/vdso: Remove --hash-style=sysv

glibc added support for .gnu.hash in 2006 and .hash has been obsoleted
for more than one decade in many Linux distributions. Using
--hash-style=sysv might imply

arm64/vdso: Remove --hash-style=sysv

glibc added support for .gnu.hash in 2006 and .hash has been obsoleted
for more than one decade in many Linux distributions. Using
--hash-style=sysv might imply unaddressed issues and confuse readers.

Just drop the option and rely on the linker default, which is likely
"both", or "gnu" when the distribution really wants to eliminate sysv
hash overhead.

Similar to commit 6b7e26547fad ("x86/vdso: Emit a GNU hash").

Signed-off-by: Fangrui Song <maskray@google.com>
Link: https://lore.kernel.org/r/20240718173423.1574395-1-maskray@google.com
Signed-off-by: Will Deacon <will@kernel.org>

show more ...

Makefile: remove redundant tool coverage variables

Now Kbuild provides reasonable defaults for objtool, sanitizers, and
profilers.

Remove redundant variables.

Note:

This commit changes the covera

Makefile: remove redundant tool coverage variables

Now Kbuild provides reasonable defaults for objtool, sanitizers, and
profilers.

Remove redundant variables.

Note:

This commit changes the coverage for some objects:

- include arch/mips/vdso/vdso-image.o into UBSAN, GCOV, KCOV
- include arch/sparc/vdso/vdso-image-*.o into UBSAN
- include arch/sparc/vdso/vma.o into UBSAN
- include arch/x86/entry/vdso/extable.o into KASAN, KCSAN, UBSAN, GCOV, KCOV
- include arch/x86/entry/vdso/vdso-image-*.o into KASAN, KCSAN, UBSAN, GCOV, KCOV
- include arch/x86/entry/vdso/vdso32-setup.o into KASAN, KCSAN, UBSAN, GCOV, KCOV
- include arch/x86/entry/vdso/vma.o into GCOV, KCOV
- include arch/x86/um/vdso/vma.o into KASAN, GCOV, KCOV

I believe these are positive effects because all of them are kernel
space objects.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Tested-by: Roberto Sassu <roberto.sassu@huawei.com>

show more ...

kbuild: use $(src) instead of $(srctree)/$(src) for source directory

Kbuild conventionally uses $(obj)/ for generated files, and $(src)/ for
checked-in source files. It is merely a convention withou

kbuild: use $(src) instead of $(srctree)/$(src) for source directory

Kbuild conventionally uses $(obj)/ for generated files, and $(src)/ for
checked-in source files. It is merely a convention without any functional
difference. In fact, $(obj) and $(src) are exactly the same, as defined
in scripts/Makefile.build:

src := $(obj)

When the kernel is built in a separate output directory, $(src) does
not accurately reflect the source directory location. While Kbuild
resolves this discrepancy by specifying VPATH=$(srctree) to search for
source files, it does not cover all cases. For example, when adding a
header search path for local headers, -I$(srctree)/$(src) is typically
passed to the compiler.

This introduces inconsistency between upstream and downstream Makefiles
because $(src) is used instead of $(srctree)/$(src) for the latter.

To address this inconsistency, this commit changes the semantics of
$(src) so that it always points to the directory in the source tree.

Going forward, the variables used in Makefiles will have the following
meanings:

$(obj) - directory in the object tree
$(src) - directory in the source tree (changed by this commit)
$(objtree) - the top of the kernel object tree
$(srctree) - the top of the kernel source tree

Consequently, $(srctree)/$(src) in upstream Makefiles need to be replaced
with $(src).

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>

show more ...

kbuild: unify vdso_install rules

Currently, there is no standard implementation for vdso_install,
leading to various issues:

1. Code duplication

Many architectures duplicate similar code just

kbuild: unify vdso_install rules

Currently, there is no standard implementation for vdso_install,
leading to various issues:

1. Code duplication

Many architectures duplicate similar code just for copying files
to the install destination.

Some architectures (arm, sparc, x86) create build-id symlinks,
introducing more code duplication.

2. Unintended updates of in-tree build artifacts

The vdso_install rule depends on the vdso files to install.
It may update in-tree build artifacts. This can be problematic,
as explained in commit 19514fc665ff ("arm, kbuild: make
"make install" not depend on vmlinux").

3. Broken code in some architectures

Makefile code is often copied from one architecture to another
without proper adaptation.

'make vdso_install' for parisc does not work.

'make vdso_install' for s390 installs vdso64, but not vdso32.

To address these problems, this commit introduces a generic vdso_install
rule.

Architectures that support vdso_install need to define vdso-install-y
in arch/*/Makefile. vdso-install-y lists the files to install.

For example, arch/x86/Makefile looks like this:

vdso-install-$(CONFIG_X86_64) += arch/x86/entry/vdso/vdso64.so.dbg
vdso-install-$(CONFIG_X86_X32_ABI) += arch/x86/entry/vdso/vdsox32.so.dbg
vdso-install-$(CONFIG_X86_32) += arch/x86/entry/vdso/vdso32.so.dbg
vdso-install-$(CONFIG_IA32_EMULATION) += arch/x86/entry/vdso/vdso32.so.dbg

These files will be installed to $(MODLIB)/vdso/ with the .dbg suffix,
if exists, stripped away.

vdso-install-y can optionally take the second field after the colon
separator. This is needed because some architectures install a vdso
file as a different base name.

The following is a snippet from arch/arm64/Makefile.

vdso-install-$(CONFIG_COMPAT_VDSO) += arch/arm64/kernel/vdso32/vdso.so.dbg:vdso32.so

This will rename vdso.so.dbg to vdso32.so during installation. If such
architectures change their implementation so that the base names match,
this workaround will go away.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Acked-by: Sven Schnelle <svens@linux.ibm.com> # s390
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>
Reviewed-by: Guo Ren <guoren@kernel.org>
Acked-by: Helge Deller <deller@gmx.de> # parisc
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>

show more ...

vdso: Improve cmd_vdso_check to check all dynamic relocations

The actual intention is that no dynamic relocation exists in the VDSO. For
this the VDSO build validates that the resulting .so file doe

vdso: Improve cmd_vdso_check to check all dynamic relocations

The actual intention is that no dynamic relocation exists in the VDSO. For
this the VDSO build validates that the resulting .so file does not have any
relocations which are specified via $(ARCH_REL_TYPE_ABS) per architecture,
which is fragile as e.g. ARM64 lacks an entry for R_AARCH64_RELATIVE. Aside
of that ARCH_REL_TYPE_ABS is a misnomer as it checks for relative
relocations too.

However, some GNU ld ports produce unneeded R_*_NONE relocation entries. If
a port fails to determine the exact .rel[a].dyn size, the trailing zeros
become R_*_NONE relocations. E.g. ld's powerpc port recently fixed
https://sourceware.org/bugzilla/show_bug.cgi?id=29540). R_*_NONE are
generally a no-op in the dynamic loaders. So just ignore them.

Remove the ARCH_REL_TYPE_ABS defines and just validate that the resulting
.so file does not contain any R_* relocation entries except R_*_NONE.

Signed-off-by: Fangrui Song <maskray@google.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Vincenzo Frascino <vincenzo.frascino@arm.com> # for aarch64
Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Reviewed-by: Vincenzo Frascino <vincenzo.frascino@arm.com> # for vDSO, aarch64
Acked-by: Michael Ellerman <mpe@ellerman.id.au> (powerpc)
Link: https://lore.kernel.org/r/20230310190750.3323802-1-maskray@google.com

show more ...

kbuild: upgrade the orphan section warning to an error if CONFIG_WERROR is set

Andrew Cooper suggested upgrading the orphan section warning to a hard link
error. However Nathan Chancellor said outri

kbuild: upgrade the orphan section warning to an error if CONFIG_WERROR is set

Andrew Cooper suggested upgrading the orphan section warning to a hard link
error. However Nathan Chancellor said outright turning the warning into an
error with no escape hatch might be too aggressive, as we have had these
warnings triggered by new compiler generated sections, and suggested turning
orphan sections into an error only if CONFIG_WERROR is set. Kees Cook echoed
and emphasized that the mandate from Linus is that we should avoid breaking
builds. It wrecks bisection, it causes problems across compiler versions, etc.

Thus upgrade the orphan section warning to a hard link error only if
CONFIG_WERROR is set.

Suggested-by: Andrew Cooper <andrew.cooper3@citrix.com>
Suggested-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Xin Li <xin3.li@intel.com>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20221025073023.16137-2-xin3.li@intel.com

show more ...

treewide: Filter out CC_FLAGS_CFI

In preparation for removing CC_FLAGS_CFI from CC_FLAGS_LTO, explicitly
filter out CC_FLAGS_CFI in all the makefiles where we currently filter
out CC_FLAGS_LTO.

Sig

treewide: Filter out CC_FLAGS_CFI

In preparation for removing CC_FLAGS_CFI from CC_FLAGS_LTO, explicitly
filter out CC_FLAGS_CFI in all the makefiles where we currently filter
out CC_FLAGS_LTO.

Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Tested-by: Kees Cook <keescook@chromium.org>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20220908215504.3686827-2-samitolvanen@google.com

show more ...

arm64: vdso: enable orphan handling for VDSO

Like vmlinux, enable orphan-handling for the VDSO. This can catch
subtle errors that might arise from unexpected sections being included.

Signed-off-by:

arm64: vdso: enable orphan handling for VDSO

Like vmlinux, enable orphan-handling for the VDSO. This can catch
subtle errors that might arise from unexpected sections being included.

Signed-off-by: Joey Gouly <joey.gouly@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Masahiro Yamada <masahiroy@kernel.org>
Cc: Vincenzo Frascino <vincenzo.frascino@arm.com>
Cc: Kees Cook <keescook@chromium.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Link: https://lore.kernel.org/r/20220510095834.32394-3-joey.gouly@arm.com
Signed-off-by: Will Deacon <will@kernel.org>

show more ...

Merge tag 'kernel-hardening-v5.19-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux

Pull kernel hardening updates from Kees Cook:

- usercopy hardening expanded to check other alloca

Merge tag 'kernel-hardening-v5.19-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux

Pull kernel hardening updates from Kees Cook:

- usercopy hardening expanded to check other allocation types (Matthew
Wilcox, Yuanzheng Song)

- arm64 stackleak behavioral improvements (Mark Rutland)

- arm64 CFI code gen improvement (Sami Tolvanen)

- LoadPin LSM block dev API adjustment (Christoph Hellwig)

- Clang randstruct support (Bill Wendling, Kees Cook)

* tag 'kernel-hardening-v5.19-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux: (34 commits)
loadpin: stop using bdevname
mm: usercopy: move the virt_addr_valid() below the is_vmalloc_addr()
gcc-plugins: randstruct: Remove cast exception handling
af_unix: Silence randstruct GCC plugin warning
niu: Silence randstruct warnings
big_keys: Use struct for internal payload
gcc-plugins: Change all version strings match kernel
randomize_kstack: Improve docs on requirements/rationale
lkdtm/stackleak: fix CONFIG_GCC_PLUGIN_STACKLEAK=n
arm64: entry: use stackleak_erase_on_task_stack()
stackleak: add on/off stack variants
lkdtm/stackleak: check stack boundaries
lkdtm/stackleak: prevent unexpected stack usage
lkdtm/stackleak: rework boundary management
lkdtm/stackleak: avoid spurious failure
stackleak: rework poison scanning
stackleak: rework stack high bound handling
stackleak: clarify variable names
stackleak: rework stack low bound handling
stackleak: remove redundant check
...

show more ...

arm64: vdso: fix makefile dependency on vdso.so

There is currently no dependency for vdso*-wrap.S on vdso*.so, which means that
you can get a build that uses a stale vdso*-wrap.o.

In commit a5b8ca9

arm64: vdso: fix makefile dependency on vdso.so

There is currently no dependency for vdso*-wrap.S on vdso*.so, which means that
you can get a build that uses a stale vdso*-wrap.o.

In commit a5b8ca97fbf8, the file that includes the vdso.so was moved and renamed
from arch/arm64/kernel/vdso/vdso.S to arch/arm64/kernel/vdso-wrap.S, when this
happened the Makefile was not updated to force the dependcy on vdso.so.

Fixes: a5b8ca97fbf8 ("arm64: do not descend to vdso directories twice")
Signed-off-by: Joey Gouly <joey.gouly@arm.com>
Cc: Masahiro Yamada <masahiroy@kernel.org>
Cc: Vincenzo Frascino <vincenzo.frascino@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20220510102721.50811-1-joey.gouly@arm.com
Signed-off-by: Will Deacon <will@kernel.org>

show more ...

randstruct: Split randstruct Makefile and CFLAGS

To enable the new Clang randstruct implementation[1], move
randstruct into its own Makefile and split the CFLAGS from
GCC_PLUGINS_CFLAGS into RANDSTR

randstruct: Split randstruct Makefile and CFLAGS

To enable the new Clang randstruct implementation[1], move
randstruct into its own Makefile and split the CFLAGS from
GCC_PLUGINS_CFLAGS into RANDSTRUCT_CFLAGS.

[1] https://reviews.llvm.org/D121556

Cc: linux-hardening@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20220503205503.3054173-5-keescook@chromium.org

show more ...

arm64: vdso: Fix "no previous prototype" warning

If compiling the arm64 kernel with W=1 the following warning is produced:

| arch/arm64/kernel/vdso/vgettimeofday.c:9:5: error: no previous prototype

arm64: vdso: Fix "no previous prototype" warning

If compiling the arm64 kernel with W=1 the following warning is produced:

| arch/arm64/kernel/vdso/vgettimeofday.c:9:5: error: no previous prototype for ‘__kernel_clock_gettime’ [-Werror=missing-prototypes]
| 9 | int __kernel_clock_gettime(clockid_t clock,
| | ^~~~~~~~~~~~~~~~~~~~~~
| arch/arm64/kernel/vdso/vgettimeofday.c:15:5: error: no previous prototype for ‘__kernel_gettimeofday’ [-Werror=missing-prototypes]
| 15 | int __kernel_gettimeofday(struct __kernel_old_timeval *tv,
| | ^~~~~~~~~~~~~~~~~~~~~
| arch/arm64/kernel/vdso/vgettimeofday.c:21:5: error: no previous prototype for ‘__kernel_clock_getres’ [-Werror=missing-prototypes]
| 21 | int __kernel_clock_getres(clockid_t clock_id,
| | ^~~~~~~~~~~~~~~~~~~~~

This patch removes "-Wmissing-prototypes" and "-Wmissing-declarations" compilers
flags from the compilation of vgettimeofday.c to make possible to build the
kernel with CONFIG_WERROR enabled.

Cc: Will Deacon <will@kernel.org>
Reported-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Tested-by: Marc Kleine-Budde <mkl@pengutronix.de>
Link: https://lore.kernel.org/r/20220121121234.47273-1-vincenzo.frascino@arm.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

show more ...

arm64: Enable KCSAN

This patch enables KCSAN for arm64, with updates to build rules
to not use KCSAN for several incompatible compilation units.

Recent GCC version(at least GCC10) made outline-atom

arm64: Enable KCSAN

This patch enables KCSAN for arm64, with updates to build rules
to not use KCSAN for several incompatible compilation units.

Recent GCC version(at least GCC10) made outline-atomics as the
default option(unlike Clang), which will cause linker errors
for kernel/kcsan/core.o. Disables the out-of-line atomics by
no-outline-atomics to fix the linker errors.

Meanwhile, as Mark said[1], some latent issues are needed to be
fixed which isn't just a KCSAN problem, we make the KCSAN depends
on EXPERT for now.

Tested selftest and kcsan_test(built with GCC11 and Clang 13),
and all passed.

[1] https://lkml.kernel.org/r/YadiUPpJ0gADbiHQ@FVFF77S0Q05N

Acked-by: Marco Elver <elver@google.com> # kernel/kcsan
Tested-by: Joey Gouly <joey.gouly@arm.com>
Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Link: https://lore.kernel.org/r/20211211131734.126874-1-wangkefeng.wang@huawei.com
[catalin.marinas@arm.com: added comment to justify EXPERT]
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

show more ...

arm64: vdso: remove -nostdlib compiler flag

The -nostdlib option requests the compiler to not use the standard
system startup files or libraries when linking. It is effective only
when $(CC) is used

arm64: vdso: remove -nostdlib compiler flag

The -nostdlib option requests the compiler to not use the standard
system startup files or libraries when linking. It is effective only
when $(CC) is used as a linker driver.

Since commit 691efbedc60d ("arm64: vdso: use $(LD) instead of $(CC)
to link VDSO"), $(LD) is directly used, hence -nostdlib is unneeded.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Link: https://lore.kernel.org/r/20211107161802.323125-1-masahiroy@kernel.org
Signed-off-by: Will Deacon <will@kernel.org>

show more ...

Merge tag 'clang-lto-v5.12-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux

Pull clang LTO updates from Kees Cook:
"Clang Link Time Optimization.

This is built on the work done p

Merge tag 'clang-lto-v5.12-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux

Pull clang LTO updates from Kees Cook:
"Clang Link Time Optimization.

This is built on the work done preparing for LTO by arm64 folks,
tracing folks, etc. This includes the core changes as well as the
remaining pieces for arm64 (LTO has been the default build method on
Android for about 3 years now, as it is the prerequisite for the
Control Flow Integrity protections).

While x86 LTO enablement is done, it depends on some pending objtool
clean-ups. It's possible that I'll send a "part 2" pull request for
LTO that includes x86 support.

For merge log posterity, and as detailed in commit dc5723b02e52
("kbuild: add support for Clang LTO"), here is the lt;dr to do an LTO
build:

make LLVM=1 LLVM_IAS=1 defconfig
scripts/config -e LTO_CLANG_THIN
make LLVM=1 LLVM_IAS=1

(To do a cross-compile of arm64, add "CROSS_COMPILE=aarch64-linux-gnu-"
and "ARCH=arm64" to the "make" command lines.)

Summary:

- Clang LTO build infrastructure and arm64-specific enablement (Sami
Tolvanen)

- Recursive build CC_FLAGS_LTO fix (Alexander Lobakin)"

* tag 'clang-lto-v5.12-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux:
kbuild: prevent CC_FLAGS_LTO self-bloating on recursive rebuilds
arm64: allow LTO to be selected
arm64: disable recordmcount with DYNAMIC_FTRACE_WITH_REGS
arm64: vdso: disable LTO
drivers/misc/lkdtm: disable LTO for rodata.o
efi/libstub: disable LTO
scripts/mod: disable LTO for empty.c
modpost: lto: strip .lto from module names
PCI: Fix PREL32 relocations for LTO
init: lto: fix PREL32 relocations
init: lto: ensure initcall ordering
kbuild: lto: add a default list of used symbols
kbuild: lto: merge module sections
kbuild: lto: limit inlining
kbuild: lto: fix module versioning
kbuild: add support for Clang LTO
tracing: move function tracer options to Kconfig

show more ...

arm64: do not descend to vdso directories twice

arm64 descends into each vdso directory twice; first in vdso_prepare,
second during the ordinary build process.

PPC mimicked it and uncovered a probl

arm64: do not descend to vdso directories twice

arm64 descends into each vdso directory twice; first in vdso_prepare,
second during the ordinary build process.

PPC mimicked it and uncovered a problem [1]. In the first descend,
Kbuild directly visits the vdso directories, therefore it does not
inherit subdir-ccflags-y from upper directories.

This means the command line parameters may differ between the two.
If it happens, the offset values in the generated headers might be
different from real offsets of vdso.so in the kernel.

This potential danger should be avoided. The vdso directories are
built in the vdso_prepare stage, so the second descend is unneeded.

[1]: https://lore.kernel.org/linux-kbuild/CAK7LNARAkJ3_-4gX0VA2UkapbOftuzfSTVMBbgbw=HD8n7N+7w@mail.gmail.com/T/#ma10dcb961fda13f36d42d58fa6cb2da988b7e73a

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Link: https://lore.kernel.org/r/20201218024540.1102650-1-masahiroy@kernel.org
Signed-off-by: Will Deacon <will@kernel.org>

show more ...

arm64: vdso: disable LTO

Disable LTO for the vDSO by filtering out CC_FLAGS_LTO, as there's no
point in using link-time optimization for the small amount of C code.

Signed-off-by: Sami Tolvanen <sa

arm64: vdso: disable LTO

Disable LTO for the vDSO by filtering out CC_FLAGS_LTO, as there's no
point in using link-time optimization for the small amount of C code.

Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Acked-by: Will Deacon <will@kernel.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20201211184633.3213045-15-samitolvanen@google.com

show more ...

arm64: vdso: disable .eh_frame_hdr via /DISCARD/ instead of --no-eh-frame-hdr

Currently with ld.lld we emit an empty .eh_frame_hdr section (and a
corresponding program header) into the vDSO. With ld

arm64: vdso: disable .eh_frame_hdr via /DISCARD/ instead of --no-eh-frame-hdr

Currently with ld.lld we emit an empty .eh_frame_hdr section (and a
corresponding program header) into the vDSO. With ld.bfd the section
is not emitted but the program header is, with p_vaddr set to 0. This
can lead to unwinders attempting to interpret the data at whichever
location the program header happens to point to as an unwind info
header. This happens to be mostly harmless as long as the byte at
that location (interpreted as a version number) has a value other
than 1, causing both libgcc and LLVM libunwind to ignore the section
(in libunwind's case, after printing an error message to stderr),
but it could lead to worse problems if the byte happened to be 1 or
the program header points to non-readable memory (e.g. if the empty
section was placed at a page boundary).

Instead of disabling .eh_frame_hdr via --no-eh-frame-hdr (which
also has the downside of being unsupported by older versions of GNU
binutils), disable it by discarding the section, and stop emitting
the program header that points to it.

I understand that we intend to emit valid unwind info for the vDSO
at some point. Once that happens this patch can be reverted.

Signed-off-by: Peter Collingbourne <pcc@google.com>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Acked-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Link: https://linux-review.googlesource.com/id/If745fd9cadcb31b4010acbf5693727fe111b0863
Link: https://lore.kernel.org/r/20201230221954.2007257-1-pcc@google.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

show more ...

arm64: lto: Strengthen READ_ONCE() to acquire when CONFIG_LTO=y

When building with LTO, there is an increased risk of the compiler
converting an address dependency headed by a READ_ONCE() invocation

arm64: lto: Strengthen READ_ONCE() to acquire when CONFIG_LTO=y

When building with LTO, there is an increased risk of the compiler
converting an address dependency headed by a READ_ONCE() invocation
into a control dependency and consequently allowing for harmful
reordering by the CPU.

Ensure that such transformations are harmless by overriding the generic
READ_ONCE() definition with one that provides acquire semantics when
building with LTO.

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>

show more ...

Merge tag 'kbuild-v5.10' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild

Pull Kbuild updates from Masahiro Yamada:

- Support 'make compile_commands.json' to generate the co

Merge tag 'kbuild-v5.10' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild

Pull Kbuild updates from Masahiro Yamada:

- Support 'make compile_commands.json' to generate the compilation
database more easily, avoiding stale entries

- Support 'make clang-analyzer' and 'make clang-tidy' for static checks
using clang-tidy

- Preprocess scripts/modules.lds.S to allow CONFIG options in the
module linker script

- Drop cc-option tests from compiler flags supported by our minimal
GCC/Clang versions

- Use always 12-digits commit hash for CONFIG_LOCALVERSION_AUTO=y

- Use sha1 build id for both BFD linker and LLD

- Improve deb-pkg for reproducible builds and rootless builds

- Remove stale, useless scripts/namespace.pl

- Turn -Wreturn-type warning into error

- Fix build error of deb-pkg when CONFIG_MODULES=n

- Replace 'hostname' command with more portable 'uname -n'

- Various Makefile cleanups

* tag 'kbuild-v5.10' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild: (34 commits)
kbuild: Use uname for LINUX_COMPILE_HOST detection
kbuild: Only add -fno-var-tracking-assignments for old GCC versions
kbuild: remove leftover comment for filechk utility
treewide: remove DISABLE_LTO
kbuild: deb-pkg: clean up package name variables
kbuild: deb-pkg: do not build linux-headers package if CONFIG_MODULES=n
kbuild: enforce -Werror=return-type
scripts: remove namespace.pl
builddeb: Add support for all required debian/rules targets
builddeb: Enable rootless builds
builddeb: Pass -n to gzip for reproducible packages
kbuild: split the build log of kallsyms
kbuild: explicitly specify the build id style
scripts/setlocalversion: make git describe output more reliable
kbuild: remove cc-option test of -Werror=date-time
kbuild: remove cc-option test of -fno-stack-check
kbuild: remove cc-option test of -fno-strict-overflow
kbuild: move CFLAGS_{KASAN,UBSAN,KCSAN} exports to relevant Makefiles
kbuild: remove redundant CONFIG_KASAN check from scripts/Makefile.kasan
kbuild: do not create built-in objects for external module builds
...

show more ...

treewide: remove DISABLE_LTO

This change removes all instances of DISABLE_LTO from
Makefiles, as they are currently unused, and the preferred
method of disabling LTO is to filter out the flags inste

treewide: remove DISABLE_LTO

This change removes all instances of DISABLE_LTO from
Makefiles, as they are currently unused, and the preferred
method of disabling LTO is to filter out the flags instead.

Note added by Masahiro Yamada:
DISABLE_LTO was added as preparation for GCC LTO, but GCC LTO was
not pulled into the mainline. (https://lkml.org/lkml/2014/4/8/272)

Suggested-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

show more ...