prog: support snapshot-only calls

Update #5308

3 files changed, 27 insertions, 20 deletions

diff --git a/docs/syscall_descriptions_syntax.md b/docs/syscall_descriptions_syntax.md
index 366903d2c..aa03c48a4 100644
--- a/docs/syscall_descriptions_syntax.md
+++ b/docs/syscall_descriptions_syntax.md
@@ -95,7 +95,7 @@ Call attributes are:
 ```
 "disabled": the call will not be used in fuzzing; useful to temporary disable some calls
 	or prohibit particular argument combinations.
-"timeout[N]": additional execution timeout (in ms) for the call on top of some default value
+"timeout[N]": additional execution timeout (in ms) for the call on top of some default value.
 "prog_timeout[N]": additional execution timeout (in ms) for the whole program if it contains this call;
 	if a program contains several such calls, the max value is used.
 "ignore_return": ignore return value of this syscall in fallback feedback; need to be used for calls
@@ -107,9 +107,13 @@ Call attributes are:
 	Without that, the fuzzer will sometimes attempt to replace complex structures with arrays of bytes,
 	possibly triggering interesting mutations, but also making programs hard to reason about.
 "fsck": the content of the compressed buffer argument for this syscall is a file system and the
-    string argument is a fsck-like command that will be called to verify the filesystem
+	string argument is a fsck-like command that will be called to verify the filesystem.
 "remote_cover": wait longer to collect remote coverage for this call.
-"kfuzz_test": the call is a kfuzztest target
+"kfuzz_test": the call is a kfuzztest target.
+"snapshot": the call is enabled by default only in snapshot fuzzing mode,
+	but "enable_syscalls" and "disable_syscalls" config parameters override this.
+	It is generally used to mark calls that are not safe to execute in non-snapshot mode
+	(can lead to false positives, or lost connections to test machines.
 ```
 
 ## Ints
diff --git a/pkg/mgrconfig/load.go b/pkg/mgrconfig/load.go
index dec412b9d..531dc26d8 100644
--- a/pkg/mgrconfig/load.go
+++ b/pkg/mgrconfig/load.go
@@ -112,21 +112,20 @@ func DefaultValues() *Config {
 type DescriptionsMode int
 
 const (
-	invalidDescriptions = iota
-	ManualDescriptions
+	ManualDescriptions = 1 << iota
 	AutoDescriptions
-	AnyDescriptions
+	SnapshotDescriptions
+
+	AnyDescriptions = ManualDescriptions | AutoDescriptions
 )
 
 const manualDescriptions = "manual"
 
-var (
-	strToDescriptionsMode = map[string]DescriptionsMode{
-		manualDescriptions: ManualDescriptions,
-		"auto":             AutoDescriptions,
-		"any":              AnyDescriptions,
-	}
-)
+var strToDescriptionsMode = map[string]DescriptionsMode{
+	manualDescriptions: ManualDescriptions,
+	"auto":             AutoDescriptions,
+	"any":              AnyDescriptions,
+}
 
 func SetTargets(cfg *Config) error {
 	var err error
@@ -184,9 +183,13 @@ func Complete(cfg *Config) error {
 		return fmt.Errorf("fuzzing_vms cannot be less than 0")
 	}
 
+	descriptionsMode := strToDescriptionsMode[cfg.Experimental.DescriptionsMode]
+	if cfg.Snapshot {
+		descriptionsMode |= SnapshotDescriptions
+	}
 	var err error
 	cfg.Syscalls, err = ParseEnabledSyscalls(cfg.Target, cfg.EnabledSyscalls, cfg.DisabledSyscalls,
-		strToDescriptionsMode[cfg.Experimental.DescriptionsMode])
+		descriptionsMode)
 	if err != nil {
 		return err
 	}
@@ -419,10 +422,6 @@ func SplitTarget(str string) (os, vmarch, arch string, target *prog.Target, sysT
 
 func ParseEnabledSyscalls(target *prog.Target, enabled, disabled []string,
 	descriptionsMode DescriptionsMode) ([]int, error) {
-	if descriptionsMode == invalidDescriptions {
-		return nil, fmt.Errorf("config param descriptions_mode must contain one of auto/manual/any")
-	}
-
 	syscalls := make(map[int]bool)
 	if len(enabled) != 0 {
 		for _, c := range enabled {
@@ -439,14 +438,17 @@ func ParseEnabledSyscalls(target *prog.Target, enabled, disabled []string,
 		}
 	} else {
 		for _, call := range target.Syscalls {
+			if call.Attrs.Snapshot && (descriptionsMode&SnapshotDescriptions) == 0 {
+				continue
+			}
 			syscalls[call.ID] = true
 		}
 	}
 
 	for call := range syscalls {
 		if target.Syscalls[call].Attrs.Disabled ||
-			descriptionsMode == ManualDescriptions && target.Syscalls[call].Attrs.Automatic ||
-			descriptionsMode == AutoDescriptions &&
+			(descriptionsMode&AutoDescriptions) == 0 && target.Syscalls[call].Attrs.Automatic ||
+			(descriptionsMode&ManualDescriptions) == 0 &&
 				!target.Syscalls[call].Attrs.Automatic && !target.Syscalls[call].Attrs.AutomaticHelper {
 			delete(syscalls, call)
 		}
diff --git a/prog/types.go b/prog/types.go
index 2329c348f..1d636fbda 100644
--- a/prog/types.go
+++ b/prog/types.go
@@ -49,6 +49,7 @@ type SyscallAttrs struct {
 	Automatic       bool
 	AutomaticHelper bool
 	KFuzzTest       bool
+	Snapshot        bool
 	Fsck            string
 	// Filesystem is used in tools/syz-imagegen when fs name cannot be deduced from
 	// the part after $.