objtool: Validate disassembler headers in libopcodes probegrafted

commit 3f2de814c059 ("objtool: Fix libopcodes linking with static libraries")
tested for libopcodes availability by linking a test snippet with a forward
declaration of disassemble_init_for_target().

However, testing symbol linkage with an extern declaration only verifies
the presence of the library (.so/.a) and bypasses checking for development
headers (binutils-dev). On systems where libopcodes is present without
development headers installed, the probe succeeds, enabling BUILD_DISAS.
Subsequent compilation of objtool then fails:

  fatal error: 'bfd.h' file not found
    113 | #include <bfd.h>

Additionally, the probe invokes $(HOSTCC) without $(HOSTCFLAGS), ignoring
any sysroot or include flags specified for the host compiler.

Fix this by including <bfd.h> and <dis-asm.h> directly in the test snippet,
passing $(HOSTCFLAGS) so host compiler options are respected, and defining
PACKAGE="objtool" to satisfy the configuration check in <bfd.h>.

Fixes: 3f2de814c059 ("objtool: Fix libopcodes linking with static libraries")
Fixes: 436326bc525d ("objtool: fix build failure due to missing libopcodes check")
Reported-by: Alice Ryhl <aliceryhl@google.com>
Assisted-by: Antigravity:Gemini-Next
Signed-off-by: Ulises Mendez Martinez <umendez@google.com>
Link: https://patch.msgid.link/20260904150710.2997558-1-umendez@google.com
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>

1 files changed, 106 insertions, 0 deletions

diff --git a/scripts/Makefile.kasan b/scripts/Makefile.kasan
new file mode 100644
index 000000000..91504e812
--- /dev/null
+++ b/scripts/Makefile.kasan
@@ -0,0 +1,106 @@
+# SPDX-License-Identifier: GPL-2.0
+
+ifdef CONFIG_CC_HAS_KASAN_MEMINTRINSIC_PREFIX
+# Safe for compiler to generate meminstrinsic calls in uninstrumented files.
+CFLAGS_KASAN_NOSANITIZE :=
+else
+# Don't let compiler generate memintrinsic calls in uninstrumented files
+# because they are instrumented.
+CFLAGS_KASAN_NOSANITIZE := -fno-builtin
+endif
+
+KASAN_SHADOW_OFFSET ?= $(CONFIG_KASAN_SHADOW_OFFSET)
+
+cc-param = $(call cc-option, -mllvm -$(1), $(call cc-option, --param $(1)))
+rustc-param = $(call rustc-option, -Cllvm-args=-$(1),)
+
+check-args = $(foreach arg,$(2),$(call $(1),$(arg)))
+
+kasan_params :=
+
+ifdef CONFIG_KASAN_STACK
+	stack_enable := 1
+else
+	stack_enable := 0
+endif
+
+ifdef CONFIG_KASAN_GENERIC
+
+ifdef CONFIG_KASAN_INLINE
+	# When the number of memory accesses in a function is less than this
+	# call threshold number, the compiler will use inline instrumentation.
+	# 10000 is chosen offhand as a sufficiently large number to make all
+	# kernel functions to be instrumented inline.
+	call_threshold := 10000
+else
+	call_threshold := 0
+endif
+
+# First, enable -fsanitize=kernel-address together with providing the shadow
+# mapping offset, as for GCC, -fasan-shadow-offset fails without -fsanitize
+# (GCC accepts the shadow mapping offset via -fasan-shadow-offset instead of
+# a --param like the other KASAN parameters).
+# Instead of ifdef-checking the compiler, rely on cc-option.
+CFLAGS_KASAN := $(call cc-option, -fsanitize=kernel-address \
+		-fasan-shadow-offset=$(KASAN_SHADOW_OFFSET), \
+		$(call cc-option, -fsanitize=kernel-address \
+		-mllvm -asan-mapping-offset=$(KASAN_SHADOW_OFFSET)))
+
+# The minimum supported `rustc` version has a minimum supported LLVM
+# version late enough that we can assume support for -asan-mapping-offset.
+RUSTFLAGS_KASAN := -Zsanitizer=kernel-address \
+		   -Zsanitizer-recover=kernel-address \
+		   -Cllvm-args=-asan-mapping-offset=$(KASAN_SHADOW_OFFSET)
+
+# Now, add other parameters enabled similarly in GCC, Clang, and rustc.
+# As some of them are not supported by older compilers, these will be filtered
+# through `cc-param` or `rust-param` as applicable.
+kasan_params += asan-instrumentation-with-call-threshold=$(call_threshold) \
+		asan-stack=$(stack_enable) \
+		asan-instrument-allocas=1 \
+		asan-globals=1
+
+# Instrument memcpy/memset/memmove calls by using instrumented __asan_mem*()
+# instead. With compilers that don't support this option, compiler-inserted
+# memintrinsics won't be checked by KASAN on GENERIC_ENTRY architectures.
+kasan_params += asan-kernel-mem-intrinsic-prefix=1
+
+endif # CONFIG_KASAN_GENERIC
+
+ifdef CONFIG_KASAN_SW_TAGS
+
+CFLAGS_KASAN := -fsanitize=kernel-hwaddress
+
+RUSTFLAGS_KASAN := -Zsanitizer=kernel-hwaddress \
+		   -Zsanitizer-recover=kernel-hwaddress
+
+ifdef CONFIG_KASAN_INLINE
+	kasan_params += hwasan-mapping-offset=$(KASAN_SHADOW_OFFSET)
+else
+	kasan_params += hwasan-instrument-with-calls=1
+endif
+
+kasan_params += hwasan-instrument-stack=$(stack_enable) \
+		hwasan-use-short-granules=0 \
+		hwasan-inline-all-checks=0
+
+# Instrument memcpy/memset/memmove calls by using instrumented __(hw)asan_mem*().
+ifdef CONFIG_CC_HAS_KASAN_MEMINTRINSIC_PREFIX
+	ifdef CONFIG_CC_IS_GCC
+		kasan_params += asan-kernel-mem-intrinsic-prefix=1
+	else
+		kasan_params += hwasan-kernel-mem-intrinsic-prefix=1
+	endif
+endif # CONFIG_CC_HAS_KASAN_MEMINTRINSIC_PREFIX
+
+endif # CONFIG_KASAN_SW_TAGS
+
+# Add all as-supported KASAN LLVM parameters requested by the configuration.
+CFLAGS_KASAN += $(call check-args, cc-param, $(kasan_params))
+
+ifdef CONFIG_RUST
+	# Avoid calling `rustc-param` unless Rust is enabled.
+	RUSTFLAGS_KASAN += $(call check-args, rustc-param, $(kasan_params))
+endif # CONFIG_RUST
+
+export CFLAGS_KASAN CFLAGS_KASAN_NOSANITIZE RUSTFLAGS_KASAN