test

.gitignore

@@ -2,3 +2,5 @@
 
 *.exe
 *.pdb
+
+!/test/*.exe

README.md

@@ -6,4 +6,5 @@ a PE loader for educational purposes.
 
 - https://learn.microsoft.com/en-us/windows/win32/debug/pe-format
 - https://learn.microsoft.com/en-us/archive/msdn-magazine/2002/february/inside-windows-win32-portable-executable-file-format-in-detail
-- https://learn.microsoft.com/en-us/archive/msdn-magazine/2002/march/inside-windows-an-in-depth-look-into-the-win32-portable-executable-file-format-part-2
+- https://learn.microsoft.com/en-us/archive/msdn-magazine/2002/march/inside-windows-an-in-depth-look-into-the-win32-portable-executable-file-format-part-2
+- https://learn.microsoft.com/en-us/windows/win32/dlls/dynamic-link-library-search-order

src/lib.rs

@@ -1,6 +1,11 @@
 mod sys;
 
-use std::{ffi::CStr, fmt::Debug, fs::File};
+use std::{
+    ffi::CStr,
+    fmt::Debug,
+    fs::File,
+    path::{Path, PathBuf},
+};
 
 #[derive(Clone, Copy, Debug, bytemuck::Zeroable, bytemuck::Pod)]
 #[repr(C)]
@@ -250,8 +255,8 @@ pub fn execute(pe: &[u8]) {
     );
     dbg!(section_table);
 
-    // just some arbitrary offset that probably won't collide with anything
-    let base = optional_header.image_base as usize + 0xFFFFFF0000;
+    // let's always load it at the image base for now...
+    let base = optional_header.image_base as usize;
 
     let allocation_granularity = crate::sys::allocation_granularity();
 
@@ -312,8 +317,18 @@ pub fn execute(pe: &[u8]) {
         dbg!(import_directory);
 
         let name = CStr::from_bytes_until_nul(&a[import_directory.name_rva as usize..]).unwrap();
+        if name.is_empty() {
+            // Trailing null import directory.
+            break;
+        }
         dbg!(name);
 
+        let dll = find_dll(name);
+        match dll {
+            Some(path) => eprintln!("  found {name:?} at {path:?}"),
+            None => eprintln!("  COULD NOT FIND {name:?}"),
+        }
+
         let import_lookups = bytemuck::cast_slice::<u8, u64>(
             &a[import_directory.import_lookup_table_rva as usize..],
         );
@@ -335,6 +350,15 @@ pub fn execute(pe: &[u8]) {
             }
         }
     }
+
+    eprintln!("YOLO");
+
+    unsafe {
+        let entrypoint = std::mem::transmute::<usize, unsafe fn() -> !>(
+            optional_header.address_of_entry_point as usize,
+        );
+        entrypoint();
+    };
 }
 
 fn parse_header(pe: &[u8]) -> (&CoffHeader, usize) {
@@ -357,3 +381,30 @@ fn parse_header(pe: &[u8]) -> (&CoffHeader, usize) {
         (signature_pointer as usize) + 4 + std::mem::size_of::<CoffHeader>(),
     )
 }
+
+fn find_dll(name: &CStr) -> Option<PathBuf> {
+    // https://learn.microsoft.com/en-us/windows/win32/dlls/dynamic-link-library-search-order
+    let name = name.to_str().unwrap();
+    if name.starts_with("api-") {
+        // This is an API set, essentially a virtual alias
+        // https://learn.microsoft.com/en-us/windows/win32/apiindex/windows-apisets
+        return None;
+    }
+
+    let system = sys::system_directory().unwrap();
+    eprintln!(" searching {system:?} for {name}");
+    let from_system = std::fs::read_dir(system).unwrap().find(|child| {
+        child
+            .as_ref()
+            .unwrap()
+            .file_name()
+            .to_str()
+            .unwrap()
+            .eq_ignore_ascii_case(name)
+    });
+    if let Some(from_system) = from_system {
+        return Some(from_system.unwrap().path());
+    }
+
+    None
+}

src/main.rs

@@ -14,7 +14,7 @@ fn main() {
         .open(
             std::env::args()
                 .nth(1)
-                .unwrap_or_else(|| "example_exe.exe".into()),
+                .unwrap_or_else(|| "test/example_exe.exe".into()),
         )
         .unwrap();
     let map = unsafe { memmap2::Mmap::map(&file).unwrap() };

src/sys.rs

@@ -8,13 +8,16 @@ pub(crate) enum Mode {
 
 #[cfg(windows)]
 mod imp {
-    use std::{ffi::c_void, io, u32};
+    use std::{ffi::c_void, io, path::PathBuf, u32};
 
     use windows::Win32::{
         Foundation::INVALID_HANDLE_VALUE,
         System::{
-            Memory::{FILE_MAP_EXECUTE, FILE_MAP_WRITE, PAGE_EXECUTE_READ, PAGE_EXECUTE_READWRITE, PAGE_READONLY, PAGE_READWRITE},
-            SystemInformation::SYSTEM_INFO,
+            Memory::{
+                FILE_MAP_EXECUTE, FILE_MAP_WRITE, PAGE_EXECUTE_READ, PAGE_EXECUTE_READWRITE,
+                PAGE_READONLY, PAGE_READWRITE,
+            },
+            SystemInformation::{GetSystemDirectoryW, SYSTEM_INFO},
         },
     };
 
@@ -36,7 +39,10 @@ mod imp {
         info.dwPageSize as usize
     }
 
-    pub(crate) unsafe fn anon_write_map<'a>(size: usize, address: *const ()) -> io::Result<&'a mut [u8]> {
+    pub(crate) unsafe fn anon_write_map<'a>(
+        size: usize,
+        address: *const (),
+    ) -> io::Result<&'a mut [u8]> {
         let map = windows::Win32::System::Memory::CreateFileMappingA(
             INVALID_HANDLE_VALUE,
             None,
@@ -88,6 +94,20 @@ mod imp {
             .map_err(Into::into)
         }
     }
+
+    pub(crate) fn system_directory() -> io::Result<PathBuf> {
+        let mut buf = vec![0; 1024];
+        let ret = unsafe { GetSystemDirectoryW(Some(&mut buf)) };
+        if ret == 0 {
+            Err(io::Error::last_os_error())
+        } else {
+            Ok(std::char::decode_utf16(buf)
+                .map(Result::unwrap)
+                .take_while(|c| *c != '\0')
+                .collect::<String>()
+                .into())
+        }
+    }
 }
 #[cfg(unix)]
 mod imp {