hardening fixes for v6.18-rc5

- Introduce __nocfi_generic for arm32 Clang (Nathan Chancellor)
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Merge tag 'hardening-v6.18-rc5' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux

Pull hardening fixes from Kees Cook:
 "This is a work-around for a (now fixed) corner case in the arm32 build
  with Clang KCFI enabled.

   - Introduce __nocfi_generic for arm32 Clang (Nathan Chancellor)"

* tag 'hardening-v6.18-rc5' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux:
  libeth: xdp: Disable generic kCFI pass for libeth_xdp_tx_xmit_bulk()
  ARM: Select ARCH_USES_CFI_GENERIC_LLVM_PASS
  compiler_types: Introduce __nocfi_generic

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

arch/arm/Kconfig

@@ -44,6 +44,8 @@ config ARM
 	select ARCH_USE_BUILTIN_BSWAP
 	select ARCH_USE_CMPXCHG_LOCKREF
 	select ARCH_USE_MEMTEST
+	# https://github.com/llvm/llvm-project/commit/d130f402642fba3d065aacb506cb061c899558de
+	select ARCH_USES_CFI_GENERIC_LLVM_PASS if CLANG_VERSION < 220000
 	select ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT if MMU
 	select ARCH_WANT_GENERAL_HUGETLB
 	select ARCH_WANT_IPC_PARSE_VERSION

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

include/net/libeth/xdp.h

@@ -513,7 +513,7 @@ struct libeth_xdp_tx_desc {
  * can't fail, but can send less frames if there's no enough free descriptors
  * available. The actual free space is returned by @prep from the driver.
  */
-static __always_inline u32
+static __always_inline __nocfi_generic u32
 libeth_xdp_tx_xmit_bulk(const struct libeth_xdp_tx_frame *bulk, void *xdpsq,
 			u32 n, bool unroll, u64 priv,
 			u32 (*prep)(void *xdpsq, struct libeth_xdpsq *sq),