LibAFL_qemu: Return errors from Emulator::new instead of asserting (#1197)

* qemu: Return errors from Emulator::new instead of asserting

Libraries should not `assert!` except in cases of unrecoverable (library)
programmer error. These errors are all potentially recoverable, and aren't
internal errors in `libafl_qemu` itself.

* Respond to review comments

fuzzers/fuzzbench_fork_qemu/src/fuzzer.rs

@@ -147,7 +147,7 @@ fn fuzz(
 
     let args: Vec<String> = env::args().collect();
     let env: Vec<(String, String)> = env::vars().collect();
-    let emu = Emulator::new(&args, &env);
+    let emu = Emulator::new(&args, &env)?;
 
     let mut elf_buffer = Vec::new();
     let elf = EasyElf::from_file(emu.binary_path(), &mut elf_buffer)?;

fuzzers/fuzzbench_qemu/src/fuzzer.rs

@@ -171,7 +171,7 @@ fn fuzz(
 
     let args: Vec<String> = env::args().collect();
     let env: Vec<(String, String)> = env::vars().collect();
-    let emu = Emulator::new(&args, &env);
+    let emu = Emulator::new(&args, &env).unwrap();
     //let emu = init_with_asan(&mut args, &mut env);
 
     let mut elf_buffer = Vec::new();

fuzzers/qemu_arm_launcher/src/fuzzer.rs

@@ -54,7 +54,7 @@ pub fn fuzz() {
     env::remove_var("LD_LIBRARY_PATH");
     let args: Vec<String> = env::args().collect();
     let env: Vec<(String, String)> = env::vars().collect();
-    let emu = Emulator::new(&args, &env);
+    let emu = Emulator::new(&args, &env).unwrap();
 
     let mut elf_buffer = Vec::new();
     let elf = EasyElf::from_file(emu.binary_path(), &mut elf_buffer).unwrap();

fuzzers/qemu_launcher/src/fuzzer.rs

@@ -54,7 +54,7 @@ pub fn fuzz() {
     env::remove_var("LD_LIBRARY_PATH");
     let args: Vec<String> = env::args().collect();
     let env: Vec<(String, String)> = env::vars().collect();
-    let emu = Emulator::new(&args, &env);
+    let emu = Emulator::new(&args, &env).unwrap();
 
     let mut elf_buffer = Vec::new();
     let elf = EasyElf::from_file(emu.binary_path(), &mut elf_buffer).unwrap();

fuzzers/qemu_systemmode/src/fuzzer.rs

@@ -80,7 +80,7 @@ pub fn fuzz() {
         // Initialize QEMU
         let args: Vec<String> = env::args().collect();
         let env: Vec<(String, String)> = env::vars().collect();
-        let emu = Emulator::new(&args, &env);
+        let emu = Emulator::new(&args, &env).unwrap();
 
         emu.set_breakpoint(main_addr);
         unsafe {

libafl/src/bolts/cli.rs

@@ -41,7 +41,7 @@
 //!
 //!     let env: Vec<(String, String)> = env::vars().collect();
 //!
-//!     let emu = Emulator::new(&mut options.qemu_args.to_vec(), &mut env);
+//!     let emu = Emulator::new(&mut options.qemu_args.to_vec(), &mut env).unwrap();
 //!     // do other stuff...
 //! }
 //!

libafl_qemu/src/asan.rs

@@ -16,7 +16,7 @@ use meminterval::{Interval, IntervalTree};
 use num_enum::{IntoPrimitive, TryFromPrimitive};
 
 use crate::{
-    emu::{Emulator, MemAccessInfo, SyscallHookResult},
+    emu::{EmuError, Emulator, MemAccessInfo, SyscallHookResult},
     helper::{QemuHelper, QemuHelperTuple, QemuInstrumentationFilter},
     hooks::QemuHooks,
     GuestAddr,
@@ -454,8 +454,10 @@ impl AsanGiovese {
 
 static mut ASAN_INITED: bool = false;
 
-pub fn init_with_asan(args: &mut Vec<String>, env: &mut [(String, String)]) -> Emulator {
-    assert!(!args.is_empty());
+pub fn init_with_asan(
+    args: &mut Vec<String>,
+    env: &mut [(String, String)],
+) -> Result<Emulator, EmuError> {
     let current = env::current_exe().unwrap();
     let asan_lib = fs::canonicalize(current)
         .unwrap()

libafl_qemu/src/emu.rs

@@ -3,6 +3,7 @@
 use core::{
     convert::Into,
     ffi::c_void,
+    fmt,
     mem::MaybeUninit,
     ptr::{addr_of, copy_nonoverlapping, null},
 };
@@ -673,28 +674,68 @@ pub struct Emulator {
     _private: (),
 }
 
+#[derive(Debug)]
+pub enum EmuError {
+    MultipleInstances,
+    EmptyArgs,
+    TooManyArgs(usize),
+}
+
+impl std::error::Error for EmuError {}
+
+impl fmt::Display for EmuError {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match self {
+            EmuError::MultipleInstances => {
+                write!(f, "Only one instance of the QEMU Emulator is permitted")
+            }
+            EmuError::EmptyArgs => {
+                write!(f, "QEMU emulator args cannot be empty")
+            }
+            EmuError::TooManyArgs(n) => {
+                write!(
+                    f,
+                    "Too many arguments passed to QEMU emulator ({n} > i32::MAX)"
+                )
+            }
+        }
+    }
+}
+
+impl From<EmuError> for libafl::Error {
+    fn from(err: EmuError) -> Self {
+        libafl::Error::unknown(format!("{err}"))
+    }
+}
+
 #[allow(clippy::unused_self)]
 impl Emulator {
     #[allow(clippy::must_use_candidate, clippy::similar_names)]
-    pub fn new(args: &[String], env: &[(String, String)]) -> Emulator {
+    pub fn new(args: &[String], env: &[(String, String)]) -> Result<Emulator, EmuError> {
         unsafe {
-            assert!(
-                !EMULATOR_IS_INITIALIZED,
-                "Only an instance of Emulator is permitted"
-            );
+            if EMULATOR_IS_INITIALIZED {
+                return Err(EmuError::MultipleInstances);
+            }
         }
-        assert!(!args.is_empty());
+        if args.is_empty() {
+            return Err(EmuError::EmptyArgs);
+        }
+
+        let argc = args.len();
+        if i32::try_from(argc).is_err() {
+            return Err(EmuError::TooManyArgs(argc));
+        }
+        #[allow(clippy::cast_possible_wrap)]
+        let argc = argc as i32;
+
         let args: Vec<String> = args.iter().map(|x| x.clone() + "\0").collect();
         let argv: Vec<*const u8> = args.iter().map(|x| x.as_bytes().as_ptr()).collect();
-        assert!(argv.len() < i32::MAX as usize);
         let env_strs: Vec<String> = env
             .iter()
             .map(|(k, v)| format!("{}={}\0", &k, &v))
             .collect();
         let mut envp: Vec<*const u8> = env_strs.iter().map(|x| x.as_bytes().as_ptr()).collect();
         envp.push(null());
-        #[allow(clippy::cast_possible_wrap)]
-        let argc = argv.len() as i32;
         unsafe {
             #[cfg(emulation_mode = "usermode")]
             qemu_user_init(
@@ -714,7 +755,7 @@ impl Emulator {
             }
             EMULATOR_IS_INITIALIZED = true;
         }
-        Emulator { _private: () }
+        Ok(Emulator { _private: () })
     }
 
     #[must_use]
@@ -1174,10 +1215,10 @@ pub mod pybind {
     impl Emulator {
         #[allow(clippy::needless_pass_by_value)]
         #[new]
-        fn new(args: Vec<String>, env: Vec<(String, String)>) -> Emulator {
-            Emulator {
-                emu: super::Emulator::new(&args, &env),
-            }
+        fn new(args: Vec<String>, env: Vec<(String, String)>) -> PyResult<Emulator> {
+            let emu = super::Emulator::new(&args, &env)
+                .map_err(|e| PyValueError::new_err(format!("{e}")))?;
+            Ok(Emulator { emu })
         }
 
         fn write_mem(&self, addr: GuestAddr, buf: &[u8]) {