Patch original-stack auxv and restore segment protections

src/loader.rs

@@ -80,6 +80,9 @@ pub fn load(
         .unwrap();
     let page_round_down = |addr: usize| addr / page_size * page_size;
     let page_round_up = |addr: usize| (addr + (page_size - 1)) / page_size * page_size;
+
+    let mut segments: Vec<(usize, usize, ProtFlags)> = Vec::new();
+
     for ph in elf.program_headers {
         if ph.p_type != PT_LOAD {
             continue;
@@ -104,7 +107,7 @@ pub fn load(
             mmap(
                 Some(addr),
                 size,
-                prot | ProtFlags::PROT_WRITE, // TODO: read only fix
+                prot | ProtFlags::PROT_WRITE,
                 MapFlags::MAP_PRIVATE | MapFlags::MAP_FIXED,
                 Some(&file),
                 offset,
@@ -119,6 +122,7 @@ pub fn load(
                 page_round_up(file_end_addr) - file_end_addr,
             );
         }
+        segments.push((addr.get(), size.get(), prot));
     }
 
     // Relocations (needed for musl but not glibc FWICT)
@@ -130,5 +134,12 @@ pub fn load(
         unsafe { ptr::write(dst, src) }
     }
 
+    // after relocations, so writes into not-yet-protected segments still work
+    for (addr, size, prot) in segments {
+        unsafe {
+            nix::sys::mman::mprotect(addr as *mut nix::libc::c_void, size, prot).unwrap();
+        }
+    }
+
     (base_addr, elf.header, opt_interp)
 }

src/stack.rs

@@ -10,7 +10,7 @@ use nix::{
     libc::{
         getauxval, AT_BASE, AT_CLKTCK, AT_EGID, AT_ENTRY, AT_EUID, AT_EXECFN, AT_FLAGS, AT_GID,
         AT_HWCAP, AT_NULL, AT_PAGESZ, AT_PHDR, AT_PHENT, AT_PHNUM, AT_PLATFORM, AT_RANDOM,
-        AT_SECURE, AT_UID,
+        AT_SECURE, AT_SYSINFO_EHDR, AT_UID,
     },
     sys::mman::{mmap, MapFlags, ProtFlags},
     unistd::{getegid, geteuid, getgid, getuid, SysconfVar},
@@ -69,6 +69,7 @@ impl<'a, A: AsRef<CStr>, E: AsRef<CStr>> StackBuilder<'a, A, E> {
             (AT_RANDOM, at_random_addr),
             (AT_CLKTCK, sysconf(SysconfVar::CLK_TCK)),
             (AT_HWCAP, unsafe { getauxval(AT_HWCAP) }),
+            (AT_SYSINFO_EHDR, unsafe { getauxval(AT_SYSINFO_EHDR) }),
             (AT_EGID, getegid().as_raw().into()),
             (AT_GID, getgid().as_raw().into()),
             (AT_EUID, geteuid().as_raw().into()),
@@ -153,6 +154,23 @@ impl<'a, A: AsRef<CStr>, E: AsRef<CStr>> StackBuilder<'a, A, E> {
     }
 }
 
+// start_stack (field 28) is the initial sp; unlike environ it survives setenv().
+fn original_auxv() -> Option<*mut usize> {
+    let stat = std::fs::read_to_string("/proc/self/stat").ok()?;
+    let fields = stat.rsplit_once(')')?.1;
+    let start_stack: usize = fields.split_whitespace().nth(25)?.parse().ok()?;
+    let sp = start_stack as *const usize;
+    if sp.is_null() {
+        return None;
+    }
+    let argc = unsafe { *sp };
+    let mut envp = unsafe { (sp as *const usize).add(argc + 2) };
+    while unsafe { *envp } != 0 {
+        envp = unsafe { envp.add(1) };
+    }
+    Some(unsafe { (envp as *mut usize).add(1) })
+}
+
 pub fn make_stack(
     interp_addr: Option<usize>,
     bin_addr: usize,
@@ -203,5 +221,22 @@ pub fn make_stack(
 
     unsafe { std::ptr::copy_nonoverlapping(data.as_ptr(), sp as *mut u8, data.len()) }
 
+    if let Some(mut auxv) = original_auxv() {
+        unsafe {
+            while *auxv != AT_NULL as usize {
+                let value = auxv.add(1);
+                match *auxv {
+                    x if x == AT_BASE as usize => *value = interp_addr.unwrap_or_default(),
+                    x if x == AT_PHDR as usize => *value = bin_addr + bin_header.e_phoff as usize,
+                    x if x == AT_PHNUM as usize => *value = bin_header.e_phnum as usize,
+                    x if x == AT_PHENT as usize => *value = bin_header.e_phentsize as usize,
+                    x if x == AT_ENTRY as usize => *value = bin_addr + bin_header.e_entry as usize,
+                    _ => {}
+                }
+                auxv = auxv.add(2);
+            }
+        }
+    }
+
     sp
 }