selftests/bpf: Add selftests for load-acquire and store-release instr…

…uctions

Add several ./test_progs tests:

  - arena_atomics/load_acquire
  - arena_atomics/store_release
  - verifier_load_acquire/*
  - verifier_store_release/*
  - verifier_precision/bpf_load_acquire
  - verifier_precision/bpf_store_release

The last two tests are added to check if backtrack_insn() handles the
new instructions correctly.

Additionally, the last test also makes sure that the verifier
"remembers" the value (in src_reg) we store-release into e.g. a stack
slot.  For example, if we take a look at the test program:

    #0:  r1 = 8;
      /* store_release((u64 *)(r10 - 8), r1); */
    #1:  .8byte %[store_release];
    #2:  r1 = *(u64 *)(r10 - 8);
    #3:  r2 = r10;
    #4:  r2 += r1;
    #5:  r0 = 0;
    #6:  exit;

At #1, if the verifier doesn't remember that we wrote 8 to the stack,
then later at #4 we would be adding an unbounded scalar value to the
stack pointer, which would cause the program to be rejected:

  VERIFIER LOG:
  =============
...
  math between fp pointer and register with unbounded min value is not allowed

For easier CI integration, instead of using built-ins like
__atomic_{load,store}_n() which depend on the new
__BPF_FEATURE_LOAD_ACQ_STORE_REL pre-defined macro, manually craft
load-acquire/store-release instructions using __imm_insn(), as suggested
by Eduard.

All new tests depend on:

  (1) Clang major version >= 18, and
  (2) ENABLE_ATOMICS_TESTS is defined (currently implies -mcpu=v3 or
      v4), and
  (3) JIT supports load-acquire/store-release (currently arm64 and
      x86-64)

In .../progs/arena_atomics.c:

  /* 8-byte-aligned */
  __u8 __arena_global load_acquire8_value = 0x12;
  /* 1-byte hole */
  __u16 __arena_global load_acquire16_value = 0x1234;

That 1-byte hole in the .addr_space.1 ELF section caused clang-17 to
crash:

  fatal error: error in backend: unable to write nop sequence of 1 bytes

To work around such llvm-17 CI job failures, conditionally define
__arena_global variables as 64-bit if __clang_major__ < 18, to make sure
.addr_space.1 has no holes.  Ideally we should avoid compiling this file
using clang-17 at all (arena tests depend on
__BPF_FEATURE_ADDR_SPACE_CAST, and are skipped for llvm-17 anyway), but
that is a separate topic.

Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Peilin Ye <yepeilin@google.com>
Link: https://lore.kernel.org/r/1b46c6feaf0f1b6984d9ec80e500cc7383e9da1a.1741049567.git.yepeilin@google.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

tools/testing/selftests/bpf/prog_tests/arena_atomics.c

@@ -162,6 +162,66 @@ static void test_uaf(struct arena_atomics *skel)
 	ASSERT_EQ(skel->arena->uaf_recovery_fails, 0, "uaf_recovery_fails");
 }
 
+static void test_load_acquire(struct arena_atomics *skel)
+{
+	LIBBPF_OPTS(bpf_test_run_opts, topts);
+	int err, prog_fd;
+
+	if (skel->data->skip_lacq_srel_tests) {
+		printf("%s:SKIP: ENABLE_ATOMICS_TESTS not defined, Clang doesn't support addr_space_cast, and/or JIT doesn't support load-acquire\n",
+		       __func__);
+		test__skip();
+		return;
+	}
+
+	/* No need to attach it, just run it directly */
+	prog_fd = bpf_program__fd(skel->progs.load_acquire);
+	err = bpf_prog_test_run_opts(prog_fd, &topts);
+	if (!ASSERT_OK(err, "test_run_opts err"))
+		return;
+	if (!ASSERT_OK(topts.retval, "test_run_opts retval"))
+		return;
+
+	ASSERT_EQ(skel->arena->load_acquire8_result, 0x12,
+		  "load_acquire8_result");
+	ASSERT_EQ(skel->arena->load_acquire16_result, 0x1234,
+		  "load_acquire16_result");
+	ASSERT_EQ(skel->arena->load_acquire32_result, 0x12345678,
+		  "load_acquire32_result");
+	ASSERT_EQ(skel->arena->load_acquire64_result, 0x1234567890abcdef,
+		  "load_acquire64_result");
+}
+
+static void test_store_release(struct arena_atomics *skel)
+{
+	LIBBPF_OPTS(bpf_test_run_opts, topts);
+	int err, prog_fd;
+
+	if (skel->data->skip_lacq_srel_tests) {
+		printf("%s:SKIP: ENABLE_ATOMICS_TESTS not defined, Clang doesn't support addr_space_cast, and/or JIT doesn't support store-release\n",
+		       __func__);
+		test__skip();
+		return;
+	}
+
+	/* No need to attach it, just run it directly */
+	prog_fd = bpf_program__fd(skel->progs.store_release);
+	err = bpf_prog_test_run_opts(prog_fd, &topts);
+	if (!ASSERT_OK(err, "test_run_opts err"))
+		return;
+	if (!ASSERT_OK(topts.retval, "test_run_opts retval"))
+		return;
+
+	ASSERT_EQ(skel->arena->store_release8_result, 0x12,
+		  "store_release8_result");
+	ASSERT_EQ(skel->arena->store_release16_result, 0x1234,
+		  "store_release16_result");
+	ASSERT_EQ(skel->arena->store_release32_result, 0x12345678,
+		  "store_release32_result");
+	ASSERT_EQ(skel->arena->store_release64_result, 0x1234567890abcdef,
+		  "store_release64_result");
+}
+
 void test_arena_atomics(void)
 {
 	struct arena_atomics *skel;
@@ -171,7 +231,7 @@ void test_arena_atomics(void)
 	if (!ASSERT_OK_PTR(skel, "arena atomics skeleton open"))
 		return;
 
-	if (skel->data->skip_tests) {
+	if (skel->data->skip_all_tests) {
 		printf("%s:SKIP:no ENABLE_ATOMICS_TESTS or no addr_space_cast support in clang",
 		       __func__);
 		test__skip();
@@ -198,6 +258,10 @@ void test_arena_atomics(void)
 		test_xchg(skel);
 	if (test__start_subtest("uaf"))
 		test_uaf(skel);
+	if (test__start_subtest("load_acquire"))
+		test_load_acquire(skel);
+	if (test__start_subtest("store_release"))
+		test_store_release(skel);
 
 cleanup:
 	arena_atomics__destroy(skel);

tools/testing/selftests/bpf/prog_tests/verifier.c

@@ -45,6 +45,7 @@
 #include "verifier_ldsx.skel.h"
 #include "verifier_leak_ptr.skel.h"
 #include "verifier_linked_scalars.skel.h"
+#include "verifier_load_acquire.skel.h"
 #include "verifier_loops1.skel.h"
 #include "verifier_lwt.skel.h"
 #include "verifier_map_in_map.skel.h"
@@ -80,6 +81,7 @@
 #include "verifier_spill_fill.skel.h"
 #include "verifier_spin_lock.skel.h"
 #include "verifier_stack_ptr.skel.h"
+#include "verifier_store_release.skel.h"
 #include "verifier_subprog_precision.skel.h"
 #include "verifier_subreg.skel.h"
 #include "verifier_tailcall_jit.skel.h"
@@ -173,6 +175,7 @@ void test_verifier_int_ptr(void)              { RUN(verifier_int_ptr); }
 void test_verifier_iterating_callbacks(void)  { RUN(verifier_iterating_callbacks); }
 void test_verifier_jeq_infer_not_null(void)   { RUN(verifier_jeq_infer_not_null); }
 void test_verifier_jit_convergence(void)      { RUN(verifier_jit_convergence); }
+void test_verifier_load_acquire(void)         { RUN(verifier_load_acquire); }
 void test_verifier_ld_ind(void)               { RUN(verifier_ld_ind); }
 void test_verifier_ldsx(void)                  { RUN(verifier_ldsx); }
 void test_verifier_leak_ptr(void)             { RUN(verifier_leak_ptr); }
@@ -211,6 +214,7 @@ void test_verifier_sockmap_mutate(void)       { RUN(verifier_sockmap_mutate); }
 void test_verifier_spill_fill(void)           { RUN(verifier_spill_fill); }
 void test_verifier_spin_lock(void)            { RUN(verifier_spin_lock); }
 void test_verifier_stack_ptr(void)            { RUN(verifier_stack_ptr); }
+void test_verifier_store_release(void)        { RUN(verifier_store_release); }
 void test_verifier_subprog_precision(void)    { RUN(verifier_subprog_precision); }
 void test_verifier_subreg(void)               { RUN(verifier_subreg); }
 void test_verifier_tailcall_jit(void)         { RUN(verifier_tailcall_jit); }

tools/testing/selftests/bpf/progs/arena_atomics.c

@@ -6,6 +6,8 @@
 #include <stdbool.h>
 #include <stdatomic.h>
 #include "bpf_arena_common.h"
+#include "../../../include/linux/filter.h"
+#include "bpf_misc.h"
 
 struct {
 	__uint(type, BPF_MAP_TYPE_ARENA);
@@ -19,9 +21,17 @@ struct {
 } arena SEC(".maps");
 
 #if defined(ENABLE_ATOMICS_TESTS) && defined(__BPF_FEATURE_ADDR_SPACE_CAST)
-bool skip_tests __attribute((__section__(".data"))) = false;
+bool skip_all_tests __attribute((__section__(".data"))) = false;
 #else
-bool skip_tests = true;
+bool skip_all_tests = true;
+#endif
+
+#if defined(ENABLE_ATOMICS_TESTS) &&		  \
+	defined(__BPF_FEATURE_ADDR_SPACE_CAST) && \
+	(defined(__TARGET_ARCH_arm64) || defined(__TARGET_ARCH_x86))
+bool skip_lacq_srel_tests __attribute((__section__(".data"))) = false;
+#else
+bool skip_lacq_srel_tests = true;
 #endif
 
 __u32 pid = 0;
@@ -274,4 +284,111 @@ int uaf(const void *ctx)
 	return 0;
 }
 
+#if __clang_major__ >= 18
+__u8 __arena_global load_acquire8_value = 0x12;
+__u16 __arena_global load_acquire16_value = 0x1234;
+__u32 __arena_global load_acquire32_value = 0x12345678;
+__u64 __arena_global load_acquire64_value = 0x1234567890abcdef;
+
+__u8 __arena_global load_acquire8_result = 0;
+__u16 __arena_global load_acquire16_result = 0;
+__u32 __arena_global load_acquire32_result = 0;
+__u64 __arena_global load_acquire64_result = 0;
+#else
+/* clang-17 crashes if the .addr_space.1 ELF section has holes. Work around
+ * this issue by defining the below variables as 64-bit.
+ */
+__u64 __arena_global load_acquire8_value;
+__u64 __arena_global load_acquire16_value;
+__u64 __arena_global load_acquire32_value;
+__u64 __arena_global load_acquire64_value;
+
+__u64 __arena_global load_acquire8_result;
+__u64 __arena_global load_acquire16_result;
+__u64 __arena_global load_acquire32_result;
+__u64 __arena_global load_acquire64_result;
+#endif
+
+SEC("raw_tp/sys_enter")
+int load_acquire(const void *ctx)
+{
+#if defined(ENABLE_ATOMICS_TESTS) &&		  \
+	defined(__BPF_FEATURE_ADDR_SPACE_CAST) && \
+	(defined(__TARGET_ARCH_arm64) || defined(__TARGET_ARCH_x86))
+
+#define LOAD_ACQUIRE_ARENA(SIZEOP, SIZE, SRC, DST)	\
+	{ asm volatile (				\
+	"r1 = %[" #SRC "] ll;"				\
+	"r1 = addr_space_cast(r1, 0x0, 0x1);"		\
+	".8byte %[load_acquire_insn];"			\
+	"r3 = %[" #DST "] ll;"				\
+	"r3 = addr_space_cast(r3, 0x0, 0x1);"		\
+	"*(" #SIZE " *)(r3 + 0) = r2;"			\
+	:						\
+	: __imm_addr(SRC),				\
+	  __imm_insn(load_acquire_insn,			\
+		     BPF_ATOMIC_OP(BPF_##SIZEOP, BPF_LOAD_ACQ,	\
+				   BPF_REG_2, BPF_REG_1, 0)),	\
+	  __imm_addr(DST)				\
+	: __clobber_all); }				\
+
+	LOAD_ACQUIRE_ARENA(B, u8, load_acquire8_value, load_acquire8_result)
+	LOAD_ACQUIRE_ARENA(H, u16, load_acquire16_value,
+			   load_acquire16_result)
+	LOAD_ACQUIRE_ARENA(W, u32, load_acquire32_value,
+			   load_acquire32_result)
+	LOAD_ACQUIRE_ARENA(DW, u64, load_acquire64_value,
+			   load_acquire64_result)
+#undef LOAD_ACQUIRE_ARENA
+
+#endif
+	return 0;
+}
+
+#if __clang_major__ >= 18
+__u8 __arena_global store_release8_result = 0;
+__u16 __arena_global store_release16_result = 0;
+__u32 __arena_global store_release32_result = 0;
+__u64 __arena_global store_release64_result = 0;
+#else
+/* clang-17 crashes if the .addr_space.1 ELF section has holes. Work around
+ * this issue by defining the below variables as 64-bit.
+ */
+__u64 __arena_global store_release8_result;
+__u64 __arena_global store_release16_result;
+__u64 __arena_global store_release32_result;
+__u64 __arena_global store_release64_result;
+#endif
+
+SEC("raw_tp/sys_enter")
+int store_release(const void *ctx)
+{
+#if defined(ENABLE_ATOMICS_TESTS) &&		  \
+	defined(__BPF_FEATURE_ADDR_SPACE_CAST) && \
+	(defined(__TARGET_ARCH_arm64) || defined(__TARGET_ARCH_x86))
+
+#define STORE_RELEASE_ARENA(SIZEOP, DST, VAL)	\
+	{ asm volatile (			\
+	"r1 = " VAL ";"				\
+	"r2 = %[" #DST "] ll;"			\
+	"r2 = addr_space_cast(r2, 0x0, 0x1);"	\
+	".8byte %[store_release_insn];"		\
+	:					\
+	: __imm_addr(DST),			\
+	  __imm_insn(store_release_insn,	\
+		     BPF_ATOMIC_OP(BPF_##SIZEOP, BPF_STORE_REL,	\
+				   BPF_REG_2, BPF_REG_1, 0))	\
+	: __clobber_all); }			\
+
+	STORE_RELEASE_ARENA(B, store_release8_result, "0x12")
+	STORE_RELEASE_ARENA(H, store_release16_result, "0x1234")
+	STORE_RELEASE_ARENA(W, store_release32_result, "0x12345678")
+	STORE_RELEASE_ARENA(DW, store_release64_result,
+			    "0x1234567890abcdef ll")
+#undef STORE_RELEASE_ARENA
+
+#endif
+	return 0;
+}
+
 char _license[] SEC("license") = "GPL";