fix(dl-tls): TLS overallocation

* `offset` is the offset in TLS to copy initial data to NOT the segment
  size
* Only zero the region which is required to be zeroed

Signed-off-by: Anhad Singh <andypython@protonmail.com>

src/ld_so/dso.rs

@@ -612,7 +612,8 @@ impl DSO {
                     };
                     tcb_master = Some(Master {
                         ptr,
-                        len: ph.p_filesz(endian) as usize,
+                        image_size: ph.p_filesz(endian) as usize,
+                        segment_size: ph.p_memsz(endian) as usize,
                         offset: tls_offset + ph.p_memsz(endian) as usize,
                     });
                     trace!("  tcb master {:x?}", tcb_master);

src/ld_so/mod.rs

@@ -33,7 +33,8 @@ pub use generic_rt::{ExpectTlsFree, panic_notls};
 
 static mut STATIC_TCB_MASTER: Master = Master {
     ptr: ptr::null_mut(),
-    len: 0,
+    image_size: 0,
+    segment_size: 0,
     offset: 0,
 };
 
@@ -112,7 +113,7 @@ pub fn static_init(
 
             unsafe {
                 STATIC_TCB_MASTER.ptr = p_vaddr as *const u8;
-                STATIC_TCB_MASTER.len = p_filesz;
+                STATIC_TCB_MASTER.image_size = p_filesz;
                 STATIC_TCB_MASTER.offset = valign;
 
                 let tcb = Tcb::new(vsize).expect_notls("failed to allocate TCB");

src/ld_so/tcb.rs

@@ -26,7 +26,8 @@ pub struct Master {
     /// Pointer to initial data
     pub ptr: *const u8,
     /// Length of initial data in bytes
-    pub len: usize,
+    pub image_size: usize,
+    pub segment_size: usize,
     /// Offset in TLS to copy initial data to
     pub offset: usize,
 }
@@ -34,7 +35,7 @@ pub struct Master {
 impl Master {
     /// The initial data for this TLS region
     pub unsafe fn data(&self) -> &'static [u8] {
-        unsafe { slice::from_raw_parts(self.ptr, self.len) }
+        unsafe { slice::from_raw_parts(self.ptr, self.image_size) }
     }
 }
 
@@ -157,13 +158,14 @@ impl Tcb {
                 for master in masters
                     .iter()
                     .skip(self.num_copied_masters)
-                    .filter(|master| master.len != 0)
+                    .filter(|master| master.image_size != 0)
                 {
                     let range = if cfg!(any(target_arch = "x86", target_arch = "x86_64")) {
                         // x86{_64} TLS layout is backwards
-                        self.tls_len - master.offset..self.tls_len - master.offset + master.len
+                        self.tls_len - master.offset
+                            ..self.tls_len - master.offset + master.image_size
                     } else {
-                        master.offset..master.offset + master.len
+                        master.offset..master.offset + master.image_size
                     };
                     if let Some(tls_data) = tls.get_mut(range) {
                         let data = unsafe { master.data() };