selftests/bpf: Prevent misaligned memory access in get_stack_raw_tp test

Perfbuf doesn't guarantee 8-byte alignment of the data like BPF ringbuf
does, so struct get_stack_trace_t can arrive not properly aligned for
subsequent u64 accesses. Easiest fix is to just copy data locally.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20211124002325.1737739-10-andrii@kernel.org

diff --git a/tools/testing/selftests/bpf/prog_tests/get_stack_raw_tp.c b/tools/testing/selftests/bpf/prog_tests/get_stack_raw_tp.c
index 4184c39..977ab43 100644 (file)
--- a/tools/testing/selftests/bpf/prog_tests/get_stack_raw_tp.c
+++ b/tools/testing/selftests/bpf/prog_tests/get_stack_raw_tp.c
@@ -24,13 +24,19 @@ static void get_stack_print_output(void *ctx, int cpu, void *data, __u32 size)
 {
        bool good_kern_stack = false, good_user_stack = false;
        const char *nonjit_func = "___bpf_prog_run";
-       struct get_stack_trace_t *e = data;
+       /* perfbuf-submitted data is 4-byte aligned, but we need 8-byte
+        * alignment, so copy data into a local variable, for simplicity
+        */
+       struct get_stack_trace_t e;
        int i, num_stack;
        static __u64 cnt;
        struct ksym *ks;
 
        cnt++;
 
+       memset(&e, 0, sizeof(e));
+       memcpy(&e, data, size <= sizeof(e) ? size : sizeof(e));
+
        if (size < sizeof(struct get_stack_trace_t)) {
                __u64 *raw_data = data;
                bool found = false;
@@ -57,19 +63,19 @@ static void get_stack_print_output(void *ctx, int cpu, void *data, __u32 size)
                        good_user_stack = true;
                }
        } else {
-               num_stack = e->kern_stack_size / sizeof(__u64);
+               num_stack = e.kern_stack_size / sizeof(__u64);
                if (env.jit_enabled) {
                        good_kern_stack = num_stack > 0;
                } else {
                        for (i = 0; i < num_stack; i++) {
-                               ks = ksym_search(e->kern_stack[i]);
+                               ks = ksym_search(e.kern_stack[i]);
                                if (ks && (strcmp(ks->name, nonjit_func) == 0)) {
                                        good_kern_stack = true;
                                        break;
                                }
                        }
                }
-               if (e->user_stack_size > 0 && e->user_stack_buildid_size > 0)
+               if (e.user_stack_size > 0 && e.user_stack_buildid_size > 0)
                        good_user_stack = true;
        }