linux.git/arch/arm64/kernel/vdso, branch v5.17

arm64: vdso: Fix "no previous prototype" warning

2022-01-24T12:08:28+00:00

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 
Reported-by: Marc Kleine-Budde 
Signed-off-by: Vincenzo Frascino 
Tested-by: Marc Kleine-Budde 
Link: https://lore.kernel.org/r/20220121121234.47273-1-vincenzo.frascino@arm.com
Signed-off-by: Catalin Marinas

arm64: Enable KCSAN

2021-12-14T18:54:34+00:00

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  # kernel/kcsan
Tested-by: Joey Gouly 
Signed-off-by: Kefeng Wang 
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

arm64: vdso: remove -nostdlib compiler flag

2021-11-08T10:02:57+00:00

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 
Link: https://lore.kernel.org/r/20211107161802.323125-1-masahiroy@kernel.org
Signed-off-by: Will Deacon

arm64/vdso: Discard .note.gnu.property sections in vDSO

2021-04-30T17:25:39+00:00

The arm64 assembler in binutils 2.32 and above generates a program
property note in a note section, .note.gnu.property, to encode used x86
ISAs and features. But the kernel linker script only contains a single
NOTE segment:

  PHDRS
  {
    text    PT_LOAD    FLAGS(5) FILEHDR PHDRS; /* PF_R|PF_X */
    dynamic PT_DYNAMIC FLAGS(4);               /* PF_R */
    note    PT_NOTE    FLAGS(4);               /* PF_R */
  }

The NOTE segment generated by the vDSO linker script is aligned to 4 bytes.
But the .note.gnu.property section must be aligned to 8 bytes on arm64.

  $ readelf -n vdso64.so

  Displaying notes found in: .note
    Owner                Data size      Description
    Linux                0x00000004     Unknown note type: (0x00000000)
     description data: 06 00 00 00
  readelf: Warning: note with invalid namesz and/or descsz found at offset 0x20
  readelf: Warning:  type: 0x78, namesize: 0x00000100, descsize: 0x756e694c, alignment: 8

Since the note.gnu.property section in the vDSO is not checked by the
dynamic linker, discard the .note.gnu.property sections in the vDSO.

Similar to commit 4caffe6a28d31 ("x86/vdso: Discard .note.gnu.property
sections in vDSO"), but for arm64.

Signed-off-by: Bill Wendling 
Reviewed-by: Kees Cook 
Acked-by: Ard Biesheuvel 
Link: https://lore.kernel.org/r/20210423205159.830854-1-morbo@google.com
Signed-off-by: Catalin Marinas

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

2021-02-23T17:28:51+00:00

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

arm64: Support running gen_vdso_offsets.sh with BSD userland.

2021-01-20T12:23:27+00:00

BSD sed ignores whitespace character escape sequences such as '\t' in
the replacement string, causing this script to produce the following
incorrect output:

  #define vdso_offset_sigtrampt0x089c

Changing the hard tab to ' ' causes both BSD and GNU dialects of sed
to produce equivalent output.

Signed-off-by: John Millikin 
Link: https://lore.kernel.org/r/15147ffb-7e67-b607-266d-f56599ecafd1@john-millikin.com
Signed-off-by: Will Deacon

arm64: do not descend to vdso directories twice

2021-01-20T12:18:46+00:00

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 
Link: https://lore.kernel.org/r/20201218024540.1102650-1-masahiroy@kernel.org
Signed-off-by: Will Deacon

arm64: vdso: disable LTO

2021-01-14T16:21:09+00:00

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 
Reviewed-by: Kees Cook 
Acked-by: Will Deacon 
Signed-off-by: Kees Cook 
Link: https://lore.kernel.org/r/20201211184633.3213045-15-samitolvanen@google.com

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

2021-01-05T17:52:13+00:00

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 
Acked-by: Ard Biesheuvel 
Acked-by: Vincenzo Frascino 
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

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

2020-11-09T21:49:34+00:00

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) 
Acked-by: Mark Rutland 
Signed-off-by: Will Deacon