bpf: Add bpf_probe_write_user BPF helper to be called in tracers
[muen/linux.git] / kernel / trace / bpf_trace.c
index a12bbd32c0a64ebe42689b411928709189df5b07..b20438fdb0295a5fdedee44b6c1ae4b8cf229200 100644 (file)
@@ -81,6 +81,49 @@ static const struct bpf_func_proto bpf_probe_read_proto = {
        .arg3_type      = ARG_ANYTHING,
 };
 
+static u64 bpf_probe_write_user(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5)
+{
+       void *unsafe_ptr = (void *) (long) r1;
+       void *src = (void *) (long) r2;
+       int size = (int) r3;
+
+       /*
+        * Ensure we're in user context which is safe for the helper to
+        * run. This helper has no business in a kthread.
+        *
+        * access_ok() should prevent writing to non-user memory, but in
+        * some situations (nommu, temporary switch, etc) access_ok() does
+        * not provide enough validation, hence the check on KERNEL_DS.
+        */
+
+       if (unlikely(in_interrupt() ||
+                    current->flags & (PF_KTHREAD | PF_EXITING)))
+               return -EPERM;
+       if (unlikely(segment_eq(get_fs(), KERNEL_DS)))
+               return -EPERM;
+       if (!access_ok(VERIFY_WRITE, unsafe_ptr, size))
+               return -EPERM;
+
+       return probe_kernel_write(unsafe_ptr, src, size);
+}
+
+static const struct bpf_func_proto bpf_probe_write_user_proto = {
+       .func           = bpf_probe_write_user,
+       .gpl_only       = true,
+       .ret_type       = RET_INTEGER,
+       .arg1_type      = ARG_ANYTHING,
+       .arg2_type      = ARG_PTR_TO_STACK,
+       .arg3_type      = ARG_CONST_STACK_SIZE,
+};
+
+static const struct bpf_func_proto *bpf_get_probe_write_proto(void)
+{
+       pr_warn_ratelimited("%s[%d] is installing a program with bpf_probe_write_user helper that may corrupt user memory!",
+                           current->comm, task_pid_nr(current));
+
+       return &bpf_probe_write_user_proto;
+}
+
 /*
  * limited trace_printk()
  * only %d %u %x %ld %lu %lx %lld %llu %llx %p %s conversion specifiers allowed
@@ -362,6 +405,8 @@ static const struct bpf_func_proto *tracing_func_proto(enum bpf_func_id func_id)
                return &bpf_get_smp_processor_id_proto;
        case BPF_FUNC_perf_event_read:
                return &bpf_perf_event_read_proto;
+       case BPF_FUNC_probe_write_user:
+               return bpf_get_probe_write_proto();
        default:
                return NULL;
        }