intel PT: check for availability in VMX

Author: Marcondiro

crates/libafl_intelpt/README.md

@@ -3,3 +3,6 @@
 This module is a wrapper around the `IntelPT` kernel driver, exposing functionalities specifically crafted for `LibAFL`.
 
 At the moment only `Linux` hosts are supported.
+
+You can run `sudo -E cargo test intel_pt_check_availability -- --show-output` to check if your host has all the features
+used by this  crate.

crates/libafl_intelpt/src/lib.rs

@@ -84,6 +84,10 @@ pub fn availability_in_qemu_kvm() -> Result<(), String> {
 
     #[cfg(target_os = "linux")]
     {
+        if let Err(reason) = availability_in_vmx() {
+            reasons.push(reason);
+        }
+
         let kvm_pt_mode_path = "/sys/module/kvm_intel/parameters/pt_mode";
         // Ignore the case when the file does not exist since it has been removed.
         // KVM default is `System` mode
@@ -123,7 +127,7 @@ mod test {
 
     /// Quick way to check if your machine is compatible with Intel PT's features used by libafl
     ///
-    /// Simply run `cargo test intel_pt_check_availability -- --show-output`
+    /// Simply run `sudo -E cargo test intel_pt_check_availability -- --show-output`
     #[test]
     fn intel_pt_check_availability() {
         print!("Intel PT availability:\t\t\t");

crates/libafl_intelpt/src/linux.rs

@@ -11,6 +11,7 @@ use alloc::{
 use core::{ffi::CStr, fmt::Debug, ops::RangeInclusive, ptr};
 use std::{
     fs,
+    io::{Read, Seek, SeekFrom},
     os::{
         fd::{AsRawFd, FromRawFd, OwnedFd},
         raw::c_void,
@@ -544,7 +545,7 @@ impl Default for IntelPTBuilder {
     ///     .inherit(false)
     ///     .perf_buffer_size(128 * PAGE_SIZE + PAGE_SIZE)
     ///     .unwrap()
-    ///     .perf_aux_buffer_size(2 * 1024 * 1024)
+    ///     .perf_aux_buffer_size(4 * 1024 * 1024)
     ///     .unwrap()
     ///     .ip_filters(&[]);
     /// assert_eq!(builder, IntelPTBuilder::default());
@@ -557,7 +558,7 @@ impl Default for IntelPTBuilder {
             exclude_hv: true,
             inherit: false,
             perf_buffer_size: 128 * PAGE_SIZE + PAGE_SIZE,
-            perf_aux_buffer_size: 2 * 1024 * 1024,
+            perf_aux_buffer_size: 4 * 1024 * 1024,
             ip_filters: Vec::new(),
         }
     }
@@ -833,6 +834,31 @@ pub(crate) fn availability_in_linux() -> Result<(), String> {
     }
 }
 
+/// Check if the `MSR IA32_VMX_MISC` has bit 14 set, which indicates that Intel PT is
+/// available in VMX operations.
+pub(crate) fn availability_in_vmx() -> Result<(), String> {
+    let error_prefix = "Failed to check for PT availability in VM operations: ";
+    let mut msrs = fs::OpenOptions::new()
+        .read(true)
+        .open("/dev/cpu/0/msr")
+        .map_err(|e| {
+            format!(
+                "{error_prefix} Failed to open /dev/cpu/0/msr: {e} \
+                Make sure you have the `msr` kernel module loaded"
+            )
+        })?;
+    msrs.seek(SeekFrom::Start(0x485))
+        .map_err(|e| format!("{error_prefix} Failed to seek in /dev/cpu/0/msr: {e}"))?;
+    let mut buf = [0u8; 8];
+    msrs.read_exact(&mut buf)
+        .map_err(|e| format!("{error_prefix} Failed to read MSR 0x485: {e}"))?;
+    if buf[1] & 0b0100_0000 == 0 {
+        return Err("Intel PT is not available for VMX operations.".to_owned());
+    }
+
+    Ok(())
+}
+
 fn new_perf_event_attr_intel_pt() -> Result<perf_event_attr, Error> {
     let type_ = match &*PERF_EVENT_TYPE {
         Ok(t) => Ok(*t),