The kernel's CFI implementation uses the KCFI ABI specifically, and is
not strictly tied to a particular compiler. In preparation for GCC
supporting KCFI, rename CONFIG_CFI_CLANG to CONFIG_CFI (along with
associated options).

Use new "transitional" Kconfig option for old CONFIG_CFI_CLANG that will
enable CONFIG_CFI during olddefconfig.

Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Link: https://lore.kernel.org/r/20250923213422.1105654-3-kees@kernel.org
Signed-off-by: Kees Cook <kees@kernel.org>

In preparation for adding Clang sanitizer coverage stack depth tracking
that can support stack depth callbacks:

- Add the new top-level CONFIG_KSTACK_ERASE option which will be
  implemented either with the stackleak GCC plugin, or with the Clang
  stack depth callback support.
- Rename CONFIG_GCC_PLUGIN_STACKLEAK as needed to CONFIG_KSTACK_ERASE,
  but keep it for anything specific to the GCC plugin itself.
- Rename all exposed "STACKLEAK" names and files to "KSTACK_ERASE" (named
  for what it does rather than what it protects against), but leave as
  many of the internals alone as possible to avoid even more churn.

While here, also split "prev_lowest_stack" into CONFIG_KSTACK_ERASE_METRICS,
since that's the only place it is referenced from.

Suggested-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20250717232519.2984886-1-kees@kernel.org
Signed-off-by: Kees Cook <kees@kernel.org>

Pull Kbuild updates from Masahiro Yamada:

 - Avoid 'constexpr', which is a keyword in C23

 - Allow 'dtbs_check' and 'dt_compatible_check' run independently of
   'dt_binding_check'

 - Fix weak references to avoid GOT entries in position-independent code
   generation

 - Convert the last use of 'optional' property in arch/sh/Kconfig

 - Remove support for the 'optional' property in Kconfig

 - Remove support for Clang's ThinLTO caching, which does not work with
   the .incbin directive

 - Change the semantics of $(src) so it always points to the source
   directory, which fixes Makefile inconsistencies between upstream and
   downstream

 - Fix 'make tar-pkg' for RISC-V to produce a consistent package

 - Provide reasonable default coverage for objtool, sanitizers, and
   profilers

 - Remove redundant OBJECT_FILES_NON_STANDARD, KASAN_SANITIZE, etc.

 - Remove the last use of tristate choice in drivers/rapidio/Kconfig

 - Various cleanups and fixes in Kconfig

* tag 'kbuild-v6.10' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild: (46 commits)
  kconfig: use sym_get_choice_menu() in sym_check_prop()
  rapidio: remove choice for enumeration
  kconfig: lxdialog: remove initialization with A_NORMAL
  kconfig: m/nconf: merge two item_add_str() calls
  kconfig: m/nconf: remove dead code to display value of bool choice
  kconfig: m/nconf: remove dead code to display children of choice members
  kconfig: gconf: show checkbox for choice correctly
  kbuild: use GCOV_PROFILE and KCSAN_SANITIZE in scripts/Makefile.modfinal
  Makefile: remove redundant tool coverage variables
  kbuild: provide reasonable defaults for tool coverage
  modules: Drop the .export_symbol section from the final modules
  kconfig: use menu_list_for_each_sym() in sym_check_choice_deps()
  kconfig: use sym_get_choice_menu() in conf_write_defconfig()
  kconfig: add sym_get_choice_menu() helper
  kconfig: turn defaults and additional prompt for choice members into error
  kconfig: turn missing prompt for choice members into error
  kconfig: turn conf_choice() into void function
  kconfig: use linked list in sym_set_changed()
  kconfig: gconf: use MENU_CHANGED instead of SYMBOL_CHANGED
  kconfig: gconf: remove debug code
  ...

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>

On x86, the ordinary, position dependent small and kernel code models
only support placement of the executable in 32-bit addressable memory,
due to the use of 32-bit signed immediates to generate references to
global variables. For the kernel, this implies that all global variables
must reside in the top 2 GiB of the kernel virtual address space, where
the implicit address bits 63:32 are equal to sign bit 31.

This means the kernel code model is not suitable for other bare metal
executables such as the kexec purgatory, which can be placed arbitrarily
in the physical address space, where its address may no longer be
representable as a sign extended 32-bit quantity. For this reason,
commit

  e16c2983fba0 ("x86/purgatory: Change compiler flags from -mcmodel=kernel to -mcmodel=large to fix kexec relocation errors")

switched to the large code model, which uses 64-bit immediates for all
symbol references, including function calls, in order to avoid relying
on any assumptions regarding proximity of symbols in the final
executable.

The large code model is rarely used, clunky and the least likely to
operate in a similar fashion when comparing GCC and Clang, so it is best
avoided. This is especially true now that Clang 18 has started to emit
executable code in two separate sections (.text and .ltext), which
triggers an issue in the kexec loading code at runtime.

The SUSE bugzilla fixes tag points to gcc 13 having issues with the
large model too and that perhaps the large model should simply not be
used at all.

Instead, use the position independent small code model, which makes no
assumptions about placement but only about proximity, where all
referenced symbols must be within -/+ 2 GiB, i.e., in range for a
RIP-relative reference. Use hidden visibility to suppress the use of a
GOT, which carries absolute addresses that are not covered by static ELF
relocations, and is therefore incompatible with the kexec loader's
relocation logic.

  [ bp: Massage commit message. ]

Fixes: e16c2983fba0 ("x86/purgatory: Change compiler flags from -mcmodel=kernel to -mcmodel=large to fix kexec relocation errors")
Fixes: https://bugzilla.suse.com/show_bug.cgi?id=1211853
Closes: https://github.com/ClangBuiltLinux/linux/issues/2016
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Fangrui Song <maskray@google.com>
Acked-by: Nick Desaulniers <ndesaulniers@google.com>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Link: https://lore.kernel.org/all/20240417-x86-fix-kexec-with-llvm-18-v1-0-5383121e8fb7@kernel.org/

Step 5/10 of the namespace unification of CPU mitigations related Kconfig options.

[ mingo: Converted a few more uses in comments/messages as well. ]

Suggested-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Breno Leitao <leitao@debian.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Ariel Miculas <amiculas@cisco.com>
Acked-by: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/r/20231121160740.1249350-6-leitao@debian.org

-flto* implies -ffunction-sections. With LTO enabled, ld.lld generates
multiple .text sections for purgatory.ro:

  $ readelf -S purgatory.ro  | grep " .text"
    [ 1] .text             PROGBITS         0000000000000000  00000040
    [ 7] .text.purgatory   PROGBITS         0000000000000000  000020e0
    [ 9] .text.warn        PROGBITS         0000000000000000  000021c0
    [13] .text.sha256_upda PROGBITS         0000000000000000  000022f0
    [15] .text.sha224_upda PROGBITS         0000000000000000  00002be0
    [17] .text.sha256_fina PROGBITS         0000000000000000  00002bf0
    [19] .text.sha224_fina PROGBITS         0000000000000000  00002cc0

This causes WARNING from kexec_purgatory_setup_sechdrs():

  WARNING: CPU: 26 PID: 110894 at kernel/kexec_file.c:919
  kexec_load_purgatory+0x37f/0x390

Fix this by disabling LTO for purgatory.

[ AFAICT, x86 is the only arch that supports LTO and purgatory. ]

We could also fix this with an explicit linker script to rejoin .text.*
sections back into .text. However, given the benefit of LTOing purgatory
is small, simply disable the production of more .text.* sections for now.

Fixes: b33fff07e3e3 ("x86, build: allow LTO to be selected")
Signed-off-by: Song Liu <song@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Sami Tolvanen <samitolvanen@google.com>
Link: https://lore.kernel.org/r/20230914170138.995606-1-song@kernel.org

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
  ...

If profile-guided optimization is enabled, the purgatory ends up with
multiple .text sections.  This is not supported by kexec and crashes the
system.

Link: https://lkml.kernel.org/r/20230321-kexec_clang16-v7-2-b05c520b7296@chromium.org
Fixes: 930457057abe ("kernel/kexec_file.c: split up __kexec_load_puragory")
Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
Cc: <stable@vger.kernel.org>
Cc: Albert Ou <aou@eecs.berkeley.edu>
Cc: Baoquan He <bhe@redhat.com>
Cc: Borislav Petkov (AMD) <bp@alien8.de>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Dave Young <dyoung@redhat.com>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Palmer Dabbelt <palmer@rivosinc.com>
Cc: Paul Walmsley <paul.walmsley@sifive.com>
Cc: Philipp Rudo <prudo@redhat.com>
Cc: Ross Zwisler <zwisler@google.com>
Cc: Simon Horman <horms@kernel.org>
Cc: Steven Rostedt (Google) <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tom Rix <trix@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

With the addition of -fstrict-flex-arrays=3, struct sha256_state's
trailing array is no longer ignored by CONFIG_FORTIFY_SOURCE:

struct sha256_state {
        u32 state[SHA256_DIGEST_SIZE / 4];
        u64 count;
        u8 buf[SHA256_BLOCK_SIZE];
};

This means that the memcpy() calls with "buf" as a destination in
sha256.c's code will attempt to perform run-time bounds checking, which
could lead to calling missing functions, specifically a potential
WARN_ONCE, which isn't callable from purgatory.

Reported-by: Thorsten Leemhuis <linux@leemhuis.info>
Closes: https://lore.kernel.org/lkml/175578ec-9dec-7a9c-8d3a-43f24ff86b92@leemhuis.info/
Bisected-by: "Joan Bruguera Micó" <joanbrugueram@gmail.com>
Fixes: df8fc4e934c1 ("kbuild: Enable -fstrict-flex-arrays=3")
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: x86@kernel.org
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Masahiro Yamada <masahiroy@kernel.org>
Cc: "Peter Zijlstra (Intel)" <peterz@infradead.org>
Cc: Alyssa Ross <hi@alyssa.is>
Cc: Sami Tolvanen <samitolvanen@google.com>
Cc: Alexander Potapenko <glider@google.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Tested-by: Thorsten Leemhuis <linux@leemhuis.info>
Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
Link: https://lore.kernel.org/r/20230531003345.never.325-kees@kernel.org