selftests/bpf: Add ASAN support for libarena selftests

Expand the arena library selftest infrastructure to support
address sanitization. Add the compiler flags necessary to
compile the library under ASAN when supported.

Signed-off-by: Emil Tsalapatis <emil@etsalapatis.com>
Link: https://lore.kernel.org/r/20260426190338.4615-6-emil@etsalapatis.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

tools/testing/selftests/bpf/Makefile

@@ -79,6 +79,12 @@ ifneq ($(shell $(CLANG) --target=bpf -mcpu=help 2>&1 | grep 'v4'),)
 CLANG_CPUV4 := 1
 endif
 
+# Check whether clang supports BPF address sanitizer (requires LLVM 22+)
+CLANG_HAS_ARENA_ASAN := $(shell echo 'int x;' | \
+	$(CLANG) --target=bpf -fsanitize=kernel-address \
+	-mllvm -asan-shadow-addr-space=1 \
+	-x c -c - -o /dev/null 2>/dev/null && echo 1)
+
 # Order correspond to 'make run_tests' order
 TEST_GEN_PROGS = test_verifier test_tag test_maps test_lru_map test_progs \
 	test_sockmap \
@@ -764,6 +770,14 @@ LIBARENA_SKEL := libarena/libarena.skel.h
 $(LIBARENA_SKEL): $(INCLUDE_DIR)/vmlinux.h $(BPFOBJ) $(LIBARENA_BPF_DEPS)
 	+$(MAKE) -C libarena libarena.skel.h $(LIBARENA_MAKE_ARGS)
 
+ifneq ($(CLANG_HAS_ARENA_ASAN),)
+LIBARENA_ASAN_SKEL := libarena/libarena_asan.skel.h
+CFLAGS += -DHAS_BPF_ARENA_ASAN
+
+$(LIBARENA_ASAN_SKEL): $(INCLUDE_DIR)/vmlinux.h $(BPFOBJ) $(LIBARENA_BPF_DEPS)
+	+$(MAKE) -C libarena libarena_asan.skel.h $(LIBARENA_MAKE_ARGS)
+endif
+
 # Define test_progs test runner.
 TRUNNER_TESTS_DIR := prog_tests
 TRUNNER_BPF_PROGS_DIR := progs
@@ -788,7 +802,9 @@ TRUNNER_EXTRA_SOURCES := test_progs.c		\
 			 flow_dissector_load.h	\
 			 ip_check_defrag_frags.h	\
 			 bpftool_helpers.c	\
-			 usdt_1.c usdt_2.c
+			 usdt_1.c usdt_2.c	\
+			 $(LIBARENA_SKEL)	\
+			 $(LIBARENA_ASAN_SKEL)
 TRUNNER_LIB_SOURCES := find_bit.c
 TRUNNER_EXTRA_FILES := $(OUTPUT)/urandom_read				\
 		       $(OUTPUT)/liburandom_read.so			\
@@ -959,3 +975,7 @@ override define INSTALL_RULE
 endef
 
 libarena: $(LIBARENA_SKEL)
+
+ifneq ($(CLANG_HAS_ARENA_ASAN),)
+libarena_asan: $(LIBARENA_ASAN_SKEL)
+endif

tools/testing/selftests/bpf/libarena/Makefile

@@ -30,6 +30,7 @@ LIBBPF_INCLUDE ?= $(INCLUDE_DIR)
 # Scan src/ and selftests/ to generate the final binaries
 LIBARENA_SOURCES = $(wildcard $(LIBARENA)/src/*.bpf.c) $(wildcard $(LIBARENA)/selftests/*.bpf.c)
 LIBARENA_OBJECTS = $(notdir $(LIBARENA_SOURCES:.bpf.c=.bpf.o))
+LIBARENA_OBJECTS_ASAN = $(notdir $(LIBARENA_SOURCES:.bpf.c=_asan.bpf.o))
 
 INCLUDES = -I$(LIBARENA)/include -I$(BPFDIR)
 ifneq ($(INCLUDE_DIR),)
@@ -39,6 +40,13 @@ ifneq ($(LIBBPF_INCLUDE),)
 INCLUDES += -I$(LIBBPF_INCLUDE)
 endif
 
+ASAN_FLAGS = -fsanitize=kernel-address -fno-stack-protector -fno-builtin
+ASAN_FLAGS += -mllvm -asan-instrument-address-spaces=1 -mllvm -asan-shadow-addr-space=1
+ASAN_FLAGS += -mllvm -asan-use-stack-safety=0 -mllvm -asan-stack=0
+ASAN_FLAGS += -mllvm -asan-kernel=1
+ASAN_FLAGS += -mllvm -asan-constructor-kind=none
+ASAN_FLAGS += -mllvm -asan-destructor-kind=none
+
 # ENABLE_ATOMICS_TESTS required because we use arena spinlocks
 override BPF_CFLAGS += -DENABLE_ATOMICS_TESTS
 override BPF_CFLAGS += -O2 -g
@@ -53,17 +61,32 @@ CFLAGS += $(INCLUDES)
 vpath %.bpf.c $(LIBARENA)/src $(LIBARENA)/selftests
 vpath %.c $(LIBARENA)/src $(LIBARENA)/selftests
 
+skeletons: libarena.skel.h libarena_asan.skel.h
+.PHONY: skeletons
+
+libarena_asan.skel.h: libarena_asan.bpf.o
+	$(call msg,GEN-SKEL,libarena,$@)
+	$(Q)$(BPFTOOL) gen skeleton $< name "libarena_asan" > $@
+
 libarena.skel.h: libarena.bpf.o
 	$(call msg,GEN-SKEL,libarena,$@)
 	$(Q)$(BPFTOOL) gen skeleton $< name "libarena" > $@
 
+libarena_asan.bpf.o: $(LIBARENA_OBJECTS_ASAN)
+	$(call msg,GEN-OBJ,libarena,$@)
+	$(Q)$(BPFTOOL) gen object $@ $^
+
 libarena.bpf.o: $(LIBARENA_OBJECTS)
 	$(call msg,GEN-OBJ,libarena,$@)
 	$(Q)$(BPFTOOL) gen object $@ $^
 
+%_asan.bpf.o: %.bpf.c
+	$(call msg,CLNG-BPF,libarena,$@)
+	$(Q)$(CLANG) $(BPF_CFLAGS) $(ASAN_FLAGS) -DBPF_ARENA_ASAN $(BPF_TARGET_ENDIAN) -c $< -o $@
+
 %.bpf.o: %.bpf.c
 	$(call msg,CLNG-BPF,libarena,$@)
 	$(Q)$(CLANG) $(BPF_CFLAGS) $(BPF_TARGET_ENDIAN) -c $< -o $@
 
 clean:
-	$(Q)rm -f *.skel.h *.bpf.o
+	$(Q)rm -f *.skel.h *.bpf.o *.linked*.o

tools/testing/selftests/bpf/libarena/include/libarena/userspace.h

@@ -27,6 +27,11 @@ static inline bool libarena_is_test_prog(const char *name)
 	return strstr(name, "test_") == name;
 }
 
+static inline bool libarena_is_asan_test_prog(const char *name)
+{
+	return strstr(name, "asan_test") == name;
+}
+
 static inline int libarena_run_prog_args(int prog_fd, void *args, size_t argsize)
 {
 	LIBBPF_OPTS(bpf_test_run_opts, opts);
@@ -97,3 +102,31 @@ static inline int libarena_get_globals_pages(int arena_get_globals_fd,
 	free(vec);
 	return 0;
 }
+
+static inline int libarena_asan_init(int arena_asan_init_fd,
+				     int asan_init_fd,
+				     size_t arena_all_pages)
+{
+	LIBBPF_OPTS(bpf_test_run_opts, opts);
+	struct asan_init_args args;
+	u64 globals_pages;
+	int ret;
+
+	ret = libarena_get_globals_pages(arena_asan_init_fd,
+					 arena_all_pages, &globals_pages);
+	if (ret)
+		return ret;
+
+	args = (struct asan_init_args){
+		.arena_all_pages = arena_all_pages,
+		.arena_globals_pages = globals_pages,
+	};
+
+	opts.ctx_in = &args;
+	opts.ctx_size_in = sizeof(args);
+
+	ret = bpf_prog_test_run_opts(asan_init_fd, &opts);
+	if (ret)
+		return ret;
+	return opts.retval;
+}

tools/testing/selftests/bpf/libarena/selftests/st_asan_common.h

@@ -0,0 +1,52 @@
+// SPDX-License-Identifier: LGPL-2.1 OR BSD-2-Clause
+/* Copyright (c) 2026 Meta Platforms, Inc. and affiliates. */
+
+#pragma once
+
+#define ST_PAGES 64
+
+static inline void print_asan_map_state(void __arena *addr)
+{
+	arena_stdout("%s:%d ASAN %p -> (val: %x gran: %x set: [%s])",
+			__func__, __LINE__, addr,
+			*(s8a *)(addr), ASAN_GRANULE(addr),
+			asan_shadow_set(addr) ? "yes" : "no");
+}
+
+/*
+ * Emit an error and force the current function to exit if the ASAN
+ * violation state is unexpected. Reset the violation state after.
+ */
+static inline int asan_validate_addr(bool cond, void __arena *addr)
+{
+	if ((asan_violated != 0) == cond) {
+		asan_violated = 0;
+		return 0;
+	}
+
+	arena_stdout("%s:%d ASAN asan_violated %lx", __func__, __LINE__,
+			(u64)asan_violated);
+	print_asan_map_state(addr);
+
+	asan_violated = 0;
+
+	return -EINVAL;
+}
+
+static inline int asan_validate(void)
+{
+	if (!asan_violated)
+		return 0;
+
+	arena_stdout("%s:%d Found ASAN violation at %lx", __func__, __LINE__,
+			asan_violated);
+
+	asan_violated = 0;
+
+	return -EINVAL;
+}
+
+struct blob {
+	volatile u8 mem[59];
+	u8 oob;
+};

tools/testing/selftests/bpf/libarena/src/common.bpf.c

@@ -2,6 +2,8 @@
 /* Copyright (c) 2026 Meta Platforms, Inc. and affiliates. */
 #include <libarena/common.h>
 
+#include <libarena/asan.h>
+
 const volatile u32 zero = 0;
 
 int arena_fls(__u64 word)