Merge tag 'hardening-v6.5-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux

Pull hardening updates from Kees Cook:
 "There are three areas of note:

  A bunch of strlcpy()->strscpy() conversions ended up living in my tree
  since they were either Acked by maintainers for me to carry, or got
  ignored for multiple weeks (and were trivial changes).

  The compiler option '-fstrict-flex-arrays=3' has been enabled
  globally, and has been in -next for the entire devel cycle. This
  changes compiler diagnostics (though mainly just -Warray-bounds which
  is disabled) and potential UBSAN_BOUNDS and FORTIFY _warning_
  coverage. In other words, there are no new restrictions, just
  potentially new warnings. Any new FORTIFY warnings we've seen have
  been fixed (usually in their respective subsystem trees). For more
  details, see commit df8fc4e934c12b.

  The under-development compiler attribute __counted_by has been added
  so that we can start annotating flexible array members with their
  associated structure member that tracks the count of flexible array
  elements at run-time. It is possible (likely?) that the exact syntax
  of the attribute will change before it is finalized, but GCC and Clang
  are working together to sort it out. Any changes can be made to the
  macro while we continue to add annotations.

  As an example of that last case, I have a treewide commit waiting with
  such annotations found via Coccinelle:

    https://git.kernel.org/linus/adc5b3cb48a049563dc673f348eab7b6beba8a9b

  Also see commit dd06e72e68bcb4 for more details.

  Summary:

   - Fix KMSAN vs FORTIFY in strlcpy/strlcat (Alexander Potapenko)

   - Convert strreplace() to return string start (Andy Shevchenko)

   - Flexible array conversions (Arnd Bergmann, Wyes Karny, Kees Cook)

   - Add missing function prototypes seen with W=1 (Arnd Bergmann)

   - Fix strscpy() kerndoc typo (Arne Welzel)

   - Replace strlcpy() with strscpy() across many subsystems which were
     either Acked by respective maintainers or were trivial changes that
     went ignored for multiple weeks (Azeem Shaikh)

   - Remove unneeded cc-option test for UBSAN_TRAP (Nick Desaulniers)

   - Add KUnit tests for strcat()-family

   - Enable KUnit tests of FORTIFY wrappers under UML

   - Add more complete FORTIFY protections for strlcat()

   - Add missed disabling of FORTIFY for all arch purgatories.

   - Enable -fstrict-flex-arrays=3 globally

   - Tightening UBSAN_BOUNDS when using GCC

   - Improve checkpatch to check for strcpy, strncpy, and fake flex
     arrays

   - Improve use of const variables in FORTIFY

   - Add requested struct_size_t() helper for types not pointers

   - Add __counted_by macro for annotating flexible array size members"

* tag 'hardening-v6.5-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux: (54 commits)
  netfilter: ipset: Replace strlcpy with strscpy
  uml: Replace strlcpy with strscpy
  um: Use HOST_DIR for mrproper
  kallsyms: Replace all non-returning strlcpy with strscpy
  sh: Replace all non-returning strlcpy with strscpy
  of/flattree: Replace all non-returning strlcpy with strscpy
  sparc64: Replace all non-returning strlcpy with strscpy
  Hexagon: Replace all non-returning strlcpy with strscpy
  kobject: Use return value of strreplace()
  lib/string_helpers: Change returned value of the strreplace()
  jbd2: Avoid printing outside the boundary of the buffer
  checkpatch: Check for 0-length and 1-element arrays
  riscv/purgatory: Do not use fortified string functions
  s390/purgatory: Do not use fortified string functions
  x86/purgatory: Do not use fortified string functions
  acpi: Replace struct acpi_table_slit 1-element array with flex-array
  clocksource: Replace all non-returning strlcpy with strscpy
  string: use __builtin_memcpy() in strlcpy/strlcat
  staging: most: Replace all non-returning strlcpy with strscpy
  drm/i2c: tda998x: Replace all non-returning strlcpy with strscpy
  ...

1 files changed, 6 insertions, 0 deletions

diff --git a/Makefile b/Makefile
index e51e4d9174ab..48a044bfe062 100644
--- a/Makefile
+++ b/Makefile
@@ -1026,6 +1026,12 @@ KBUILD_CFLAGS += -Wno-pointer-sign
 # globally built with -Wcast-function-type.
 KBUILD_CFLAGS += $(call cc-option, -Wcast-function-type)
 
+# To gain proper coverage for CONFIG_UBSAN_BOUNDS and CONFIG_FORTIFY_SOURCE,
+# the kernel uses only C99 flexible arrays for dynamically sized trailing
+# arrays. Enforce this for everything that may examine structure sizes and
+# perform bounds checking.
+KBUILD_CFLAGS += $(call cc-option, -fstrict-flex-arrays=3)
+
 # disable stringop warnings in gcc 8+
 KBUILD_CFLAGS += $(call cc-disable-warning, stringop-truncation)