executor: delay kcov mmap until it is needed

The previous strategy (delay kcov instance creation) seems not to work
very well in carefully sandboxed environments. Let's see if the new
approach is more versatile.

Open a kcov handle for each thread at syz-executor's initialization, but
don't mmap it right away.

1 files changed, 10 insertions, 13 deletions

diff --git a/executor/executor_bsd.h b/executor/executor_bsd.h
index 80b56f317..dc3ebbdd8 100644
--- a/executor/executor_bsd.h
+++ b/executor/executor_bsd.h
@@ -61,7 +61,7 @@ static void cover_open(cover_t* cov, bool extra)
 #if GOOS_freebsd
 	if (ioctl(cov->fd, KIOSETBUFSIZE, kCoverSize))
 		fail("ioctl init trace write failed");
-	size_t mmap_alloc_size = kCoverSize * KCOV_ENTRY_SIZE;
+	cov->mmap_alloc_size = kCoverSize * KCOV_ENTRY_SIZE;
 #elif GOOS_openbsd
 	unsigned long cover_size = kCoverSize;
 	if (ioctl(cov->fd, KIOSETBUFSIZE, &cover_size))
@@ -73,7 +73,7 @@ static void cover_open(cover_t* cov, bool extra)
 		if (ioctl(cov->fd, KIOREMOTEATTACH, &args))
 			fail("ioctl remote attach failed");
 	}
-	size_t mmap_alloc_size = kCoverSize * (is_kernel_64_bit ? 8 : 4);
+	cov->mmap_alloc_size = kCoverSize * (is_kernel_64_bit ? 8 : 4);
 #elif GOOS_netbsd
 	uint64_t cover_size;
 	if (extra) {
@@ -90,15 +90,20 @@ static void cover_open(cover_t* cov, bool extra)
 		if (ioctl(cov->fd, KCOV_IOC_SETBUFSIZE, &cover_size))
 			fail("ioctl init trace write failed");
 	}
-	size_t mmap_alloc_size = cover_size * KCOV_ENTRY_SIZE;
+	cov->mmap_alloc_size = cover_size * KCOV_ENTRY_SIZE;
 #endif
+}
 
-	void* mmap_ptr = mmap(NULL, mmap_alloc_size, PROT_READ | PROT_WRITE,
+static void cover_mmap(cover_t* cov)
+{
+	if (cov->data != NULL)
+		fail("cover_mmap invoked on an already mmapped cover_t object");
+	void* mmap_ptr = mmap(NULL, cov->mmap_alloc_size, PROT_READ | PROT_WRITE,
 			      MAP_SHARED, cov->fd, 0);
 	if (mmap_ptr == MAP_FAILED)
 		fail("cover mmap failed");
 	cov->data = (char*)mmap_ptr;
-	cov->data_end = cov->data + mmap_alloc_size;
+	cov->data_end = cov->data + cov->mmap_alloc_size;
 	cov->data_offset = is_kernel_64_bit ? sizeof(uint64_t) : sizeof(uint32_t);
 	cov->pc_offset = 0;
 }
@@ -164,14 +169,6 @@ static void cover_collect(cover_t* cov)
 	cov->size = *(uint64*)cov->data;
 }
 
-static void cover_reserve_fd(cover_t* cov)
-{
-	int fd = open("/dev/null", O_RDONLY);
-	if (fd < 0)
-		fail("failed to open /dev/null");
-	dup2(fd, cov->fd);
-}
-
 static bool use_cover_edges(uint64 pc)
 {
 	return true;