[PATCH v2 09/12] sandbox: Add libfuzzer integration

Andrew Scull
2022-04-14T14:02:02Z

Add an implementation of LLVMFuzzerTestOneInput() that starts the
sandbox on a secondary thread and exposes a function to synchronize the
generation of fuzzing inputs with their consumption by the sandbox.

Signed-off-by: Andrew Scull <ascull@google.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
---
arch/sandbox/config.mk | 3 +
arch/sandbox/cpu/os.c | 70 +++++++++++++++++++++++
arch/sandbox/include/asm/fuzzing_engine.h | 25 ++++++++
3 files changed, 98 insertions(+)
create mode 100644 arch/sandbox/include/asm/fuzzing_engine.h

diff --git a/arch/sandbox/config.mk b/arch/sandbox/config.mk
index d7ce66fb6c..5fbe1f50e3 100644
--- a/arch/sandbox/config.mk
+++ b/arch/sandbox/config.mk
@@ -19,6 +19,9 @@ SANITIZERS :=
ifdef CONFIG_ASAN
SANITIZERS += -fsanitize=address
endif
+ifdef CONFIG_FUZZ
+SANITIZERS += -fsanitize=fuzzer
+endif
KBUILD_CFLAGS += $(SANITIZERS)

cmd_u-boot__ = $(CC) -o $@ -Wl,-T u-boot.lds $(u-boot-init) \
diff --git a/arch/sandbox/cpu/os.c b/arch/sandbox/cpu/os.c
index 5ea4135741..cd45d7b6b6 100644
--- a/arch/sandbox/cpu/os.c
+++ b/arch/sandbox/cpu/os.c
@@ -8,6 +8,7 @@
#include <dirent.h>
#include <errno.h>
#include <fcntl.h>
+#include <pthread.h>
#include <getopt.h>
#include <setjmp.h>
#include <signal.h>
@@ -26,6 +27,7 @@
#include <linux/compiler_attributes.h>
#include <linux/types.h>

+#include <asm/fuzzing_engine.h>
#include <asm/getopt.h>
#include <asm/main.h>
#include <asm/sections.h>
@@ -1002,7 +1004,75 @@ void os_relaunch(char *argv[])
os_exit(1);
}

+
+#ifdef CONFIG_FUZZ
+static void *fuzzer_thread(void * ptr)
+{
+ char cmd[64];
+ char *argv[5] = {"./u-boot", "-T", "-c", cmd, NULL};
+ const char *fuzz_test;
+
+ /* Find which test to run from an environment variable. */
+ fuzz_test = getenv("UBOOT_SB_FUZZ_TEST");
+ if (!fuzz_test)
+ os_abort();
+
+ snprintf(cmd, sizeof(cmd), "fuzz %s", fuzz_test);
+
+ sandbox_main(4, argv);
+ os_abort();
+ return NULL;
+}
+
+static bool fuzzer_initialized = false;
+static pthread_mutex_t fuzzer_mutex = PTHREAD_MUTEX_INITIALIZER;
+static pthread_cond_t fuzzer_cond = PTHREAD_COND_INITIALIZER;
+static const uint8_t *fuzzer_data;
+static size_t fuzzer_size;
+
+int sandbox_fuzzing_engine_get_input(const uint8_t **data, size_t *size)
+{
+ if (!fuzzer_initialized)
+ return -ENOSYS;
+
+ /* Tell the main thread we need new inputs then wait for them. */
+ pthread_mutex_lock(&fuzzer_mutex);
+ pthread_cond_signal(&fuzzer_cond);
+ pthread_cond_wait(&fuzzer_cond, &fuzzer_mutex);
+ *data = fuzzer_data;
+ *size = fuzzer_size;
+ pthread_mutex_unlock(&fuzzer_mutex);
+ return 0;
+}
+
+int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size)
+{
+ static pthread_t tid;
+
+ pthread_mutex_lock(&fuzzer_mutex);
+
+ /* Initialize the sandbox on another thread. */
+ if (!fuzzer_initialized) {
+ fuzzer_initialized = true;
+ if (pthread_create(&tid, NULL, fuzzer_thread, NULL))
+ os_abort();
+ pthread_cond_wait(&fuzzer_cond, &fuzzer_mutex);
+ }
+
+ /* Hand over the input. */
+ fuzzer_data = data;
+ fuzzer_size = size;
+ pthread_cond_signal(&fuzzer_cond);
+
+ /* Wait for the inputs to be finished with. */
+ pthread_cond_wait(&fuzzer_cond, &fuzzer_mutex);
+ pthread_mutex_unlock(&fuzzer_mutex);
+
+ return 0;
+}
+#else
int main(int argc, char *argv[])
{
return sandbox_main(argc, argv);
}
+#endif
diff --git a/arch/sandbox/include/asm/fuzzing_engine.h b/arch/sandbox/include/asm/fuzzing_engine.h
new file mode 100644
index 0000000000..cf6396363b
--- /dev/null
+++ b/arch/sandbox/include/asm/fuzzing_engine.h
@@ -0,0 +1,25 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * Copyright (c) 2022 Google, Inc.
+ * Written by Andrew Scull <ascull@google.com>
+ */
+
+#ifndef __ASM_FUZZING_ENGINE_H
+#define __ASM_FUZZING_ENGINE_H
+
+/** Function to get fuzzing engine input data. */
+/**
+ * sandbox_fuzzing_engine_get_input() - get an input from the sandbox fuzzing
+ * engine
+ *
+ * The function will return a pointer to the input data and the size of the
+ * data pointed to. The pointer will remain valid until the next invocation of
+ * this function.
+ *
+ * @data: output pointer to input data
+ * @size output size of input data
+ * Return: 0 if OK, -ve on error
+ */
+int sandbox_fuzzing_engine_get_input(const uint8_t **data, size_t *size);
+
+#endif /* __ASM_FUZZING_ENGINE_H */
--
2.35.1.1178.g4f1659d476-goog