From b458f2c1a61c78e2004be6b4ef60b45fb81bd684 Mon Sep 17 00:00:00 2001
From: Dmitry Vyukov <dvyukov@google.com>
Date: Mon, 13 Jul 2020 16:24:56 +0200
Subject: executor: wrap all syscalls into NONFAILING

Currently we sprinkle NONFAILING all over pseudo-syscall code,
around all individual accesses to fuzzer-generated pointers.
This is tedious manual work and subject to errors.
Wrap execute_syscall invocation with NONFAILING in execute_call once instead.
Then we can remove NONFAILING from all pseudo-syscalls and never get back to this.
Potential downsides: (1) this is coarser-grained and we will skip whole syscall
on invalid pointer, but this is how normal syscalls work as well,
so should not be a problem; (2) we will skip any clean up (closing of files, etc)
as well; but this may be fine as well (programs can perfectly leave open file
descriptors as well).

Update #1918
---
 pkg/csource/csource.go | 79 ++++++++++++++++++++++++++++++--------------------
 1 file changed, 47 insertions(+), 32 deletions(-)

(limited to 'pkg/csource')

diff --git a/pkg/csource/csource.go b/pkg/csource/csource.go
index e679468df..9cd456533 100644
--- a/pkg/csource/csource.go
+++ b/pkg/csource/csource.go
@@ -212,40 +212,24 @@ func (ctx *context) emitCall(w *bytes.Buffer, call prog.ExecCall, ci int, haveCo
 	_, trampoline := ctx.sysTarget.SyscallTrampolines[callName]
 	native := ctx.sysTarget.SyscallNumbers && !strings.HasPrefix(callName, "syz_") && !trampoline
 	fmt.Fprintf(w, "\t")
-	if haveCopyout || trace {
-		fmt.Fprintf(w, "res = ")
-	}
-	ctx.emitCallName(w, call, native)
-	for ai, arg := range call.Args {
-		if native || ai > 0 {
-			fmt.Fprintf(w, ", ")
+	if !native {
+		// This mimics the same as executor does for execute_syscall,
+		// but only for non-native syscalls to reduce clutter (native syscalls are assumed to not crash).
+		// Arrange for res = -1 in case of syscall abort, we care about errno only if we are tracing for pkg/runtest.
+		if haveCopyout || trace {
+			fmt.Fprintf(w, "res = -1;\n\t")
 		}
-		switch arg := arg.(type) {
-		case prog.ExecArgConst:
-			if arg.Format != prog.FormatNative && arg.Format != prog.FormatBigEndian {
-				panic("sring format in syscall argument")
-			}
-			fmt.Fprintf(w, "%v", ctx.constArgToStr(arg, true, native))
-		case prog.ExecArgResult:
-			if arg.Format != prog.FormatNative && arg.Format != prog.FormatBigEndian {
-				panic("sring format in syscall argument")
-			}
-			val := ctx.resultArgToStr(arg)
-			if native && ctx.target.PtrSize == 4 {
-				// syscall accepts args as ellipsis, resources are uint64
-				// and take 2 slots without the cast, which would be wrong.
-				val = "(intptr_t)" + val
-			}
-			fmt.Fprintf(w, "%v", val)
-		default:
-			panic(fmt.Sprintf("unknown arg type: %+v", arg))
+		if trace {
+			fmt.Fprintf(w, "errno = EFAULT;\n\t")
 		}
+		fmt.Fprintf(w, "NONFAILING(")
 	}
-	for i := 0; i < call.Meta.MissingArgs; i++ {
-		if native || len(call.Args) != 0 {
-			fmt.Fprintf(w, ", ")
-		}
-		fmt.Fprintf(w, "0")
+	if haveCopyout || trace {
+		fmt.Fprintf(w, "res = ")
+	}
+	ctx.emitCallBody(w, call, native)
+	if !native {
+		fmt.Fprintf(w, ")") // close NONFAILING macro
 	}
 	fmt.Fprintf(w, ");")
 	comment := ctx.target.AnnotateCall(call)
@@ -264,7 +248,7 @@ func (ctx *context) emitCall(w *bytes.Buffer, call prog.ExecCall, ci int, haveCo
 	}
 }
 
-func (ctx *context) emitCallName(w *bytes.Buffer, call prog.ExecCall, native bool) {
+func (ctx *context) emitCallBody(w *bytes.Buffer, call prog.ExecCall, native bool) {
 	callName, ok := ctx.sysTarget.SyscallTrampolines[call.Meta.CallName]
 	if !ok {
 		callName = call.Meta.CallName
@@ -280,6 +264,37 @@ func (ctx *context) emitCallName(w *bytes.Buffer, call prog.ExecCall, native boo
 		}
 		fmt.Fprintf(w, "((intptr_t(*)(%v))CAST(%v))(", args, callName)
 	}
+	for ai, arg := range call.Args {
+		if native || ai > 0 {
+			fmt.Fprintf(w, ", ")
+		}
+		switch arg := arg.(type) {
+		case prog.ExecArgConst:
+			if arg.Format != prog.FormatNative && arg.Format != prog.FormatBigEndian {
+				panic("sring format in syscall argument")
+			}
+			fmt.Fprintf(w, "%v", ctx.constArgToStr(arg, true, native))
+		case prog.ExecArgResult:
+			if arg.Format != prog.FormatNative && arg.Format != prog.FormatBigEndian {
+				panic("sring format in syscall argument")
+			}
+			val := ctx.resultArgToStr(arg)
+			if native && ctx.target.PtrSize == 4 {
+				// syscall accepts args as ellipsis, resources are uint64
+				// and take 2 slots without the cast, which would be wrong.
+				val = "(intptr_t)" + val
+			}
+			fmt.Fprintf(w, "%v", val)
+		default:
+			panic(fmt.Sprintf("unknown arg type: %+v", arg))
+		}
+	}
+	for i := 0; i < call.Meta.MissingArgs; i++ {
+		if native || len(call.Args) != 0 {
+			fmt.Fprintf(w, ", ")
+		}
+		fmt.Fprintf(w, "0")
+	}
 }
 
 func (ctx *context) generateCsumInet(w *bytes.Buffer, addr uint64, arg prog.ExecArgCsum, csumSeq int) {
-- 
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