Properly decode binary data sent via GDB commands (#2730)

pwndbg/aglib/file.py

@@ -185,7 +185,7 @@ def vfile_readlink(pathname: str | bytes) -> bytes:
 
     parts = response[1:].split(b";", 1)
     # bytes_read = int(parts[0], 16)
-    target = parts[1]
+    target = gdb_memtox_inverse(parts[1])
     return target
 
 
@@ -234,6 +234,27 @@ def vfile_open(filename: str, flags: int, mode: int) -> int:
     return file_descriptor
 
 
+# GDB defines the encoding of binary data transferred through commands here:
+# - https://sourceware.org/gdb/current/onlinedocs/gdb.html/Overview.html#:~:text=The%20binary%20data%20representation%20uses%207d
+# This function unescapes these character
+# Example of QEMU function that does this escaping:
+# https://github.com/qemu/qemu/blob/de278e54aefed143526174335f8286f7437d20be/gdbstub/gdbstub.c#L184
+def gdb_memtox_inverse(data: bytes) -> bytes:
+    buffer = bytearray()
+
+    i = 0
+    while i < len(data):
+        b = data[i]
+        if b == 125:  # == ord("}"):
+            buffer.append(data[i + 1] ^ 0x20)
+            i += 1
+        else:
+            buffer.append(b)
+        i += 1
+
+    return buffer
+
+
 def vfile_pread(fd: int, size: int, offset: int) -> Tuple[int, bytes]:
     """
     Reads data from a file descriptor.
@@ -249,7 +270,9 @@ def vfile_pread(fd: int, size: int, offset: int) -> Tuple[int, bytes]:
 
     parts = response[1:].split(b";", 1)
     bytes_read = int(parts[0].decode(), 16)
-    data = parts[1]
+    # We have to decode the data, because some bytes -  #,$,*,} - have special encodings
+    data = gdb_memtox_inverse(parts[1])
+
     return bytes_read, data