Save and restore CPU state in libafl_qemu (#907)

* libafl_qemu: fix systemmode with slirp dependency

libslirp will be dropped from future QEMU releases (see https://wiki.qemu.org/ChangeLog/7.0).
This change adds the "slirp" feature,
which links with the host-systems libslirp.

* libafl_qemu: enable systemmode snapshots, vm_start

Re-enable snapshot functions.
Start the VM before qemu_main_loop.

* libafl_qemu: allow synchronous snapshotting

Add a flag to take snapshots synchronosly.
This should be used to take or load snapshots while the emulator is not
running.

* libafl_qemu: fallback cpu for read-/write_mem

In systemmode, current_cpu may not be set.
In such cases use the first cpus memory access methods.

* fuzzers: add example for libafl_qemu in systemmode

* libafl_qemu: update libafl-qemu-bridge revision

* libafl_qemu: add memory access by physcial address

* fix liabfl_qemu example

Use GuestAddr and physical memory access

* ci: install libslirp-dev for libafl_qemu

* fuzzers/qemu_systemmode: clean up example

* libafl_qemu: remove obsolete functions

emu::libafl_cpu_thread_fn
emu::libafl_start_vcpu
emu::start

* fuzzers/qemu_systemmode: simplify example

* improve build_linux.rs

* Update qemu_systemmode fuzzer

* upd

* clippy

* Save and restore CPU state in libafl_qemu

* clippy

* Clone

* upd

* upd

Co-authored-by: Alwin Berger <alwin.berger@tu-dortmund.de>

fuzzers/qemu_systemmode/example/main.c

@@ -5,9 +5,9 @@ int BREAKPOINT() {
 }
 
 int LLVMFuzzerTestOneInput(unsigned int* Data, unsigned int Size) {
-  if (Data[3] == 0) {while(1){}}  // cause a timeout
+  //if (Data[3] == 0) {while(1){}}  // cause a timeout
   for (int i=0; i<Size; i++) {
-    if (Data[i] > 0xFFd0 && Data[i] < 0xFFFF) {return 1;}    // cause qemu to crash
+    //if (Data[i] > 0xFFd0 && Data[i] < 0xFFFF) {return 1;}    // cause qemu to crash
     for (int j=i+1; j<Size; j++) {
       if (Data[j] == 0) {continue;}
       if (Data[j]>Data[i]) {

fuzzers/qemu_systemmode/src/fuzzer.rs

@@ -99,6 +99,10 @@ pub fn fuzz() {
         //    saved_regs.push(emu.cpu_from_index(0).read_reg(r).unwrap());
         //}
 
+        let saved_cpu_states: Vec<_> = (0..emu.num_cpus())
+            .map(|i| emu.cpu_from_index(i).save_state())
+            .collect();
+
         // The wrapped harness function, calling out to the LLVM-style harness
         let mut harness = |input: &BytesInput| {
             let target = input.target_bytes();
@@ -129,7 +133,11 @@ pub fn fuzz() {
                     None => ExitKind::Crash,
                 };
 
-                emu.load_snapshot("start", true);
+                for (i, s) in saved_cpu_states.iter().enumerate() {
+                    emu.cpu_from_index(i).restore_state(s);
+                }
+
+                // emu.load_snapshot("start", true);
 
                 ret
             }

libafl_qemu/build_linux.rs

@@ -4,7 +4,7 @@ use which::which;
 
 const QEMU_URL: &str = "https://github.com/AFLplusplus/qemu-libafl-bridge";
 const QEMU_DIRNAME: &str = "qemu-libafl-bridge";
-const QEMU_REVISION: &str = "658565bec0a68a84c733217fa9b7802562096559";
+const QEMU_REVISION: &str = "f26a5ca6137bb5d4d0dcfe5451fb16d4c0551c4e";
 
 fn build_dep_check(tools: &[&str]) {
     for tool in tools {
@@ -45,7 +45,6 @@ pub fn build() {
     println!("cargo:rerun-if-env-changed=EMULATION_MODE");
 
     println!("cargo:rerun-if-changed=build.rs");
-    println!("cargo:rerun-if-env-changed=CROSS_CC");
 
     // Make sure we have at most one architecutre feature set
     // Else, we default to `x86_64` - having a default makes CI easier :)

libafl_qemu/src/emu.rs

@@ -1,12 +1,12 @@
 //! Expose QEMU user `LibAFL` C api to Rust
 
+#[cfg(emulation_mode = "usermode")]
+use core::mem::MaybeUninit;
 use core::{
     convert::Into,
     ffi::c_void,
-    ptr::{addr_of, addr_of_mut, null},
+    ptr::{addr_of, addr_of_mut, copy_nonoverlapping, null},
 };
-#[cfg(emulation_mode = "usermode")]
-use core::{mem::MaybeUninit, ptr::copy_nonoverlapping};
 use std::{ffi::CString, slice::from_raw_parts, str::from_utf8_unchecked};
 
 #[cfg(emulation_mode = "usermode")]
@@ -30,7 +30,8 @@ use pyo3::{prelude::*, PyIterProtocol};
 
 pub const SKIP_EXEC_HOOK: u64 = u64::MAX;
 
-type CPUStatePtr = *const c_void;
+type CPUStatePtr = *mut c_void;
+type CPUArchStatePtr = *mut c_void;
 
 #[derive(IntoPrimitive, TryFromPrimitive, Debug, Clone, Copy, EnumIter, PartialEq, Eq)]
 #[repr(i32)]
@@ -254,6 +255,8 @@ extern "C" fn qemu_cleanup_atexit() {
 }
 
 extern "C" {
+    fn libafl_qemu_arch_state_size() -> usize;
+
     // CPUState* libafl_qemu_get_cpu(int cpu_index);
     fn libafl_qemu_get_cpu(cpu_index: i32) -> CPUStatePtr;
     // int libafl_qemu_num_cpus(void);
@@ -356,6 +359,9 @@ extern "C" {
     );
     fn libafl_qemu_gdb_reply(buf: *const u8, len: usize);
 
+    fn libafl_qemu_cpu_arch_state(cpu: CPUStatePtr) -> CPUArchStatePtr;
+    // fn libafl_qemu_arch_state_cpu(env: CPUArchStatePtr) -> CPUStatePtr;
+
     fn cpu_reset(cpu: CPUStatePtr);
 }
 
@@ -437,6 +443,26 @@ extern "C" fn gdb_cmd(buf: *const u8, len: usize, data: *const ()) -> i32 {
     }
 }
 
+#[derive(Clone, Debug)]
+#[repr(C)]
+pub struct SavedCPUState {
+    data: Vec<u8>,
+}
+
+impl SavedCPUState {
+    #[must_use]
+    #[allow(clippy::uninit_vec)]
+    fn uninit() -> Self {
+        unsafe {
+            let len = libafl_qemu_arch_state_size();
+            let mut data = Vec::with_capacity(len);
+            data.set_len(len);
+
+            Self { data }
+        }
+    }
+}
+
 #[derive(Debug)]
 #[repr(C)]
 pub struct CPU {
@@ -540,9 +566,32 @@ impl CPU {
         }
     }
 
-    pub fn cpu_reset(&self) {
+    pub fn reset(&self) {
         unsafe { cpu_reset(self.ptr) };
     }
+
+    #[must_use]
+    pub fn save_state(&self) -> SavedCPUState {
+        let mut saved = SavedCPUState::uninit();
+        unsafe {
+            copy_nonoverlapping(
+                libafl_qemu_cpu_arch_state(self.ptr) as *mut u8,
+                saved.data.as_mut_ptr(),
+                saved.data.len(),
+            );
+        }
+        saved
+    }
+
+    pub fn restore_state(&self, saved: &SavedCPUState) {
+        unsafe {
+            copy_nonoverlapping(
+                saved.data.as_ptr(),
+                libafl_qemu_cpu_arch_state(self.ptr) as *mut u8,
+                saved.data.len(),
+            );
+        }
+    }
 }
 
 static mut EMULATOR_IS_INITIALIZED: bool = false;