selftests/bpf: Add tests for arena fault reporting

Add selftests for testing the reporting of arena page faults through BPF
streams. Two new bpf programs are added that read and write to an
unmapped arena address and the fault reporting is verified in the
userspace through streams.

The bpf programs need to access the user_vm_start in struct bpf_arena,
this is done by casting &arena to struct bpf_arena *, but barrier_var()
is used on this ptr before accessing ptr->user_vm_start; to stop GCC
from issuing an out-of-bound access due to the cast from smaller map
struct to larger "struct bpf_arena"

Signed-off-by: Puranjay Mohan <puranjay@kernel.org>

Author: puranjaymohan

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

@@ -41,6 +41,22 @@ struct {
 		"([a-zA-Z_][a-zA-Z0-9_]*\\+0x[0-9a-fA-F]+/0x[0-9a-fA-F]+\n"
 		"|[ \t]+[^\n]+\n)*",
 	},
+	{
+		offsetof(struct stream, progs.stream_arena_read_fault),
+		"ERROR: Arena READ access at unmapped address 0x.*\n"
+		"CPU: [0-9]+ UID: 0 PID: [0-9]+ Comm: .*\n"
+		"Call trace:\n"
+		"([a-zA-Z_][a-zA-Z0-9_]*\\+0x[0-9a-fA-F]+/0x[0-9a-fA-F]+\n"
+		"|[ \t]+[^\n]+\n)*",
+	},
+	{
+		offsetof(struct stream, progs.stream_arena_write_fault),
+		"ERROR: Arena WRITE access at unmapped address 0x.*\n"
+		"CPU: [0-9]+ UID: 0 PID: [0-9]+ Comm: .*\n"
+		"Call trace:\n"
+		"([a-zA-Z_][a-zA-Z0-9_]*\\+0x[0-9a-fA-F]+/0x[0-9a-fA-F]+\n"
+		"|[ \t]+[^\n]+\n)*",
+	},
 };
 
 static int match_regex(const char *pattern, const char *string)
@@ -63,6 +79,7 @@ void test_stream_errors(void)
 	struct stream *skel;
 	int ret, prog_fd;
 	char buf[1024];
+	char fault_addr[64] = {0};
 
 	skel = stream__open_and_load();
 	if (!ASSERT_OK_PTR(skel, "stream__open_and_load"))
@@ -85,15 +102,30 @@ void test_stream_errors(void)
 			continue;
 		}
 #endif
+#if !defined(__x86_64__) && !defined(__aarch64__)
+		ASSERT_TRUE(1, "Arena fault reporting unsupported, skip.");
+		if (i == 2 || i == 3) {
+			ret = bpf_prog_stream_read(prog_fd, 2, buf, sizeof(buf), &ropts);
+			ASSERT_EQ(ret, 0, "stream read");
+			continue;
+		}
+#endif
 
 		ret = bpf_prog_stream_read(prog_fd, BPF_STREAM_STDERR, buf, sizeof(buf), &ropts);
 		ASSERT_GT(ret, 0, "stream read");
 		ASSERT_LE(ret, 1023, "len for buf");
 		buf[ret] = '\0';
 
 		ret = match_regex(stream_error_arr[i].errstr, buf);
-		if (!ASSERT_TRUE(ret == 1, "regex match"))
+		if (ret && (i == 2 || i == 3)) {
+			sprintf(fault_addr, "0x%lx", skel->bss->fault_addr);
+			ret = match_regex(fault_addr, buf);
+		}
+		if (!ASSERT_TRUE(ret == 1, "regex match")) {
 			fprintf(stderr, "Output from stream:\n%s\n", buf);
+			if (i == 2 || i == 3)
+				fprintf(stderr, "Fault Addr: 0x%lx\n", skel->bss->fault_addr);
+		}
 	}
 
 	stream__destroy(skel);

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

@@ -5,6 +5,7 @@
 #include <bpf/bpf_helpers.h>
 #include "bpf_misc.h"
 #include "bpf_experimental.h"
+#include "bpf_arena_common.h"
 
 struct arr_elem {
 	struct bpf_res_spin_lock lock;
@@ -17,10 +18,17 @@ struct {
 	__type(value, struct arr_elem);
 } arrmap SEC(".maps");
 
+struct {
+	__uint(type, BPF_MAP_TYPE_ARENA);
+	__uint(map_flags, BPF_F_MMAPABLE);
+	__uint(max_entries, 1); /* number of pages */
+} arena SEC(".maps");
+
 #define ENOSPC 28
 #define _STR "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"
 
 int size;
+u64 fault_addr;
 
 SEC("syscall")
 __success __retval(0)
@@ -76,4 +84,57 @@ int stream_syscall(void *ctx)
 	return 0;
 }
 
+SEC("syscall")
+__success __retval(0)
+int stream_arena_write_fault(void *ctx)
+{
+	struct bpf_arena *ptr = (void *)&arena;
+	u64 user_vm_start;
+
+	/* Prevent GCC bounds warning: casting &arena to struct bpf_arena *
+	 * triggers bounds checking since the map definition is smaller than struct
+	 * bpf_arena. barrier_var() makes the pointer opaque to GCC, preventing the
+	 * bounds analysis
+	 */
+	barrier_var(ptr);
+	user_vm_start =  ptr->user_vm_start;
+	fault_addr = user_vm_start + 0x7fff;
+	bpf_addr_space_cast(user_vm_start, 0, 1);
+	asm volatile (
+		"r1 = %0;"
+		"r2 = 1;"
+		"*(u32 *)(r1 + 0x7fff) = r2;"
+		:
+		: "r" (user_vm_start)
+		: "r1", "r2"
+	);
+	return 0;
+}
+
+SEC("syscall")
+__success __retval(0)
+int stream_arena_read_fault(void *ctx)
+{
+	struct bpf_arena *ptr = (void *)&arena;
+	u64 user_vm_start;
+
+	/* Prevent GCC bounds warning: casting &arena to struct bpf_arena *
+	 * triggers bounds checking since the map definition is smaller than struct
+	 * bpf_arena. barrier_var() makes the pointer opaque to GCC, preventing the
+	 * bounds analysis
+	 */
+	barrier_var(ptr);
+	user_vm_start = ptr->user_vm_start;
+	fault_addr = user_vm_start + 0x7fff;
+	bpf_addr_space_cast(user_vm_start, 0, 1);
+	asm volatile (
+		"r1 = %0;"
+		"r1 = *(u32 *)(r1 + 0x7fff);"
+		:
+		: "r" (user_vm_start)
+		: "r1"
+	);
+	return 0;
+}
+
 char _license[] SEC("license") = "GPL";