compiler_types: Introduce __nocfi_generic

There are two different ways that LLVM can expand kCFI operand bundles
in LLVM IR: generically in the middle end or using an architecture
specific sequence when lowering LLVM IR to machine code in the backend.
The generic pass allows any architecture to take advantage of kCFI but
the expansion of these bundles in the middle end can mess with
optimizations that may turn indirect calls into direct calls when the
call target is known at compile time, such as after inlining.

Add __nocfi_generic, dependent on an architecture selecting
CONFIG_ARCH_USES_CFI_GENERIC_LLVM_PASS, to disable kCFI bundle
generation in functions where only the generic kCFI pass may cause
problems.

Link: https://github.com/ClangBuiltLinux/linux/issues/2124
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Link: https://patch.msgid.link/20251025-idpf-fix-arm-kcfi-build-error-v1-1-ec57221153ae@kernel.org
Signed-off-by: Kees Cook <kees@kernel.org>

diff --git a/arch/Kconfig b/arch/Kconfig
index 74ff0113353223909d07feff56defe221987182b..61130b88964b94eda9be06fc06c58a7b63e251ca 100644 (file)
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -917,6 +917,13 @@ config ARCH_USES_CFI_TRAPS
          An architecture should select this option if it requires the
          .kcfi_traps section for KCFI trap handling.
 
+config ARCH_USES_CFI_GENERIC_LLVM_PASS
+       bool
+       help
+         An architecture should select this option if it uses the generic
+         KCFIPass in LLVM to expand kCFI bundles instead of architecture-specific
+         lowering.
+
 config CFI
        bool "Use Kernel Control Flow Integrity (kCFI)"
        default CFI_CLANG

diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h
index 59288a2c1ad27700af5edafd89a0db82e85ce296..1414be493738a817defa845bf7a834782461558f 100644 (file)
--- a/include/linux/compiler_types.h
+++ b/include/linux/compiler_types.h
@@ -461,6 +461,12 @@ struct ftrace_likely_data {
 # define __nocfi
 #endif
 
+#if defined(CONFIG_ARCH_USES_CFI_GENERIC_LLVM_PASS)
+# define __nocfi_generic       __nocfi
+#else
+# define __nocfi_generic
+#endif
+
 /*
  * Any place that could be marked with the "alloc_size" attribute is also
  * a place to be marked with the "malloc" attribute, except those that may