perf trace: Warn when trying to resolve kernel addresses with kptr_restrict=1

Hook into the libtraceevent plugin kernel symbol resolver to warn the
user that that can't happen with kptr_restrict=1.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Milian Wolff <milian.wolff@kdab.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-9gc412xx1gl0lvqj1d1xwlyb@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

3 files changed, 21 insertions, 1 deletions

diff --git a/tools/perf/builtin-trace.c b/tools/perf/builtin-trace.c
index 6e5c325148e4..e488ac756f39 100644
--- a/tools/perf/builtin-trace.c
+++ b/tools/perf/builtin-trace.c
@@ -1160,6 +1160,24 @@ static int trace__tool_process(struct perf_tool *tool,
         return trace__process_event(trace, machine, event, sample);
 }
 
+static char *trace__machine__resolve_kernel_addr(void *vmachine, unsigned long long *addrp, char **modp)
+{
+        struct machine *machine = vmachine;
+
+        if (machine->kptr_restrict_warned)
+                return NULL;
+
+        if (symbol_conf.kptr_restrict) {
+                pr_warning("Kernel address maps (/proc/{kallsyms,modules}) are restricted.\n\n"
+                           "Check /proc/sys/kernel/kptr_restrict.\n\n"
+                           "Kernel samples will not be resolved.\n");
+                machine->kptr_restrict_warned = true;
+                return NULL;
+        }
+
+        return machine__resolve_kernel_addr(vmachine, addrp, modp);
+}
+
 static int trace__symbols_init(struct trace *trace, struct perf_evlist *evlist)
 {
         int err = symbol__init(NULL);
@@ -1171,7 +1189,7 @@ static int trace__symbols_init(struct trace *trace, struct perf_evlist *evlist)
         if (trace->host == NULL)
                 return -ENOMEM;
 
-        if (trace_event__register_resolver(trace->host, machine__resolve_kernel_addr) < 0)
+        if (trace_event__register_resolver(trace->host, trace__machine__resolve_kernel_addr) < 0)
                 return -errno;
 
         err = __machine__synthesize_threads(trace->host, &trace->tool, &trace->opts.target,
diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
index b277984aaa93..bdc33ce40bdc 100644
--- a/tools/perf/util/machine.c
+++ b/tools/perf/util/machine.c
@@ -43,6 +43,7 @@ int machine__init(struct machine *machine, const char *root_dir, pid_t pid)
 
         machine->symbol_filter = NULL;
         machine->id_hdr_size = 0;
+        machine->kptr_restrict_warned = false;
         machine->comm_exec = false;
         machine->kernel_start = 0;
 
diff --git a/tools/perf/util/machine.h b/tools/perf/util/machine.h
index 83f46790c52f..41ac9cfd416b 100644
--- a/tools/perf/util/machine.h
+++ b/tools/perf/util/machine.h
@@ -28,6 +28,7 @@ struct machine {
         pid_t             pid;
         u16               id_hdr_size;
         bool              comm_exec;
+        bool              kptr_restrict_warned;
         char              *root_dir;
         struct rb_root    threads;
         pthread_rwlock_t  threads_lock;