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

1 files changed, 5 insertions, 2 deletions

diff --git a/executor/executor.cc b/executor/executor.cc
index 1e7625d7e..ccbdb1aa0 100644
--- a/executor/executor.cc
+++ b/executor/executor.cc
@@ -1088,8 +1088,11 @@ void execute_call(thread_t* th)
 
 	if (flag_coverage)
 		cover_reset(&th->cov);
-	errno = 0;
-	th->res = execute_syscall(call, th->args);
+	// For pseudo-syscalls and user-space functions NONFAILING can abort before assigning to th->res.
+	// Arrange for res = -1 and errno = EFAULT result for such case.
+	th->res = -1;
+	errno = EFAULT;
+	NONFAILING(th->res = execute_syscall(call, th->args));
 	th->reserrno = errno;
 	if (th->res == -1 && th->reserrno == 0)
 		th->reserrno = EINVAL; // our syz syscalls may misbehave