pkg/vminfo: move feature checking to host

Feature checking procedure is split into 2 phases:
1. syz-fuzzer invokes "syz-executor setup feature" for each feature one-by-one,
and checks if executor does not fail.
Executor can also return a special "this feature does not need custom setup",
this allows to not call setup of these features in each new VM.
2. pkg/vminfo runs a simple program with ipc.ExecOpts specific for a concrete feature,
e.g. for wifi injection it will try to run a program with wifi feature enabled,
if setup of the feature fails, executor should also exit with an error.
For coverage features we also additionally check that we actually got coverage.
Then pkg/vminfo combines results of these 2 checks into final result.

syz-execprog now also uses vminfo package and mimics the same checking procedure.

Update #1541

1 files changed, 26 insertions, 18 deletions

diff --git a/executor/executor.cc b/executor/executor.cc
index 6ac777ad6..2e4e01da8 100644
--- a/executor/executor.cc
+++ b/executor/executor.cc
@@ -369,7 +369,7 @@ struct kcov_comparison_t {
 typedef char kcov_comparison_size[sizeof(kcov_comparison_t) == 4 * sizeof(uint64) ? 1 : -1];
 
 struct feature_t {
-	const char* name;
+	rpc::Feature id;
 	void (*setup)();
 };
 
@@ -1658,33 +1658,41 @@ bool kcov_comparison_t::operator<(const struct kcov_comparison_t& other) const
 }
 #endif // if SYZ_EXECUTOR_USES_SHMEM
 
+#if !SYZ_HAVE_FEATURES
+static feature_t features[] = {};
+#endif
+
 void setup_features(char** enable, int n)
 {
 	// This does any one-time setup for the requested features on the machine.
 	// Note: this can be called multiple times and must be idempotent.
 	flag_debug = true;
+	if (n != 1)
+		fail("setup: more than one feature");
+	char* endptr = nullptr;
+	auto feature = static_cast<rpc::Feature>(strtoull(enable[0], &endptr, 10));
+	if (endptr == enable[0] || (feature > rpc::Feature::ANY) ||
+	    __builtin_popcountll(static_cast<uint64>(feature)) > 1)
+		failmsg("setup: failed to parse feature", "feature='%s'", enable[0]);
+	if (feature == rpc::Feature::NONE) {
 #if SYZ_HAVE_FEATURES
-	setup_sysctl();
-	setup_cgroups();
+		setup_sysctl();
+		setup_cgroups();
 #endif
 #if SYZ_HAVE_SETUP_EXT
-	// This can be defined in common_ext.h.
-	setup_ext();
+		// This can be defined in common_ext.h.
+		setup_ext();
 #endif
-	for (int i = 0; i < n; i++) {
-		bool found = false;
-#if SYZ_HAVE_FEATURES
-		for (unsigned f = 0; f < sizeof(features) / sizeof(features[0]); f++) {
-			if (strcmp(enable[i], features[f].name) == 0) {
-				features[f].setup();
-				found = true;
-				break;
-			}
+		return;
+	}
+	for (size_t i = 0; i < sizeof(features) / sizeof(features[0]); i++) {
+		if (features[i].id == feature) {
+			features[i].setup();
+			return;
 		}
-#endif
-		if (!found)
-			failmsg("setup features: unknown feature", "feature=%s", enable[i]);
 	}
+	// Note: pkg/host knows about this error message.
+	fail("feature setup is not needed");
 }
 
 void failmsg(const char* err, const char* msg, ...)
@@ -1728,7 +1736,7 @@ void exitf(const char* msg, ...)
 	vfprintf(stderr, msg, args);
 	va_end(args);
 	fprintf(stderr, " (errno %d)\n", e);
-	doexit(0);
+	doexit(1);
 }
 
 void debug(const char* msg, ...)