# SPDX-FileCopyrightText: 2022 Andrius Štikonas # SPDX-FileCopyrightText: 2017 Jeremiah Orians # # SPDX-License-Identifier: GPL-3.0-or-later # Usage: hex0 file.hex0 file # Does not validate the arguments or check for success # Calling convention: # First four arguments are passed via registers rcx, rdx, r8, r9 (if they fit in 64-bits) # but we need to leave stack space # Registers: # r12 in/fin: input file name, later reused for handle # r13 out/fout: output file name, later reused for handle # r14 system->boot->open_protocol from UEFI, later reused for hex0 algorithm, later reused for rootdir # r15 image_handle from UEFI, later reused for hex0 algorithm .global _start .text _start: mov rbp, rsp # save stack pointer mov r15, rcx # save image_handle mov r14, [rdx+96] # system->boot mov r14, [r14+280] # system->boot->open_protocol # Open Loaded Image protocol push rax # allocate stack for image mov r8, rsp # arg3 = &image mov rdx, [LOADED_IMAGE_PROTOCOL+8]# EFI_LOADED_IMAGE_PROTOCOL_GUID (last 64 bits) push rdx # push last 64 bits onto stack mov rdx, [LOADED_IMAGE_PROTOCOL] # EFI_LOADED_IMAGE_PROTOCOL_GUID (first 64 bits) push rdx # push first 64 bits onto stack mov rdx, rsp # arg2 = &guid push 1 # arg6 = EFI_OPEN_PROTOCOL_BY_HANDLE_PROTOCOL push 0 # arg5 = NULL mov r9, rcx # arg4 = image_handle # arg1 = ImageHandle (already set) push rax # allocate shadow stack space for UEFI function push rax # allocate shadow stack space for UEFI function push rax # allocate shadow stack space for UEFI function push rax # allocate shadow stack space for UEFI function call r14 # system->boot->open_protocol(image_handle, &guid, &image, image_handle, 0, EFI_OPEN_PROTOCOL_BY_HANDLE_PROTOCOL); mov rax, [rsp+64] # get image # Command line args mov rcx, rax # save image mov rax, [rax+56] # options = image->load_options loop_options1: # Skip application name add rax, 2 # ++options mov bl, [rax] # *options cmp bl, 0x20 # if *options != ' ' jne loop_options1 # then jump add rax, 2 # ++options mov r12, rax loop_options2: # Skip argv[1] add rax, 2 # ++options mov bl, [rax] # *options cmp bl, 0x20 # if *options != ' ' jne loop_options2 # then jump mov byte ptr [rax], 0 # *options = 0; add rax, 2 # ++options mov r13, rax # Get root device push rax # allocate stack for rootfs mov r8, rsp # arg3 = &rootfs mov rdx, [SIMPLE_FS_PROTOCOL+8] # EFI_SIMPLE_FILE_SYSTEM_PROTOCOL_GUID (last 64 bits) push rdx # push last 64 bits onto stack mov rdx, [SIMPLE_FS_PROTOCOL] # EFI_SIMPLE_FILE_SYSTEM_PROTOCOL_GUID (first 64 bits) push rdx # push first 64 bits onto stack mov rdx, rsp # arg2 = &guid push 1 # arg6 = EFI_OPEN_PROTOCOL_BY_HANDLE_PROTOCOL push 0 # arg5 = NULL mov r9, r15 # arg4 = image_handle mov rcx, [rcx+24] # arg1 = root_device = image->device push rax # allocate shadow stack space for UEFI function push rax # allocate shadow stack space for UEFI function push rax # allocate shadow stack space for UEFI function push rax # allocate shadow stack space for UEFI function call r14 # system->boot->open_protocol(root_device, &guid, &rootfs, image_handle, 0, EFI_OPEN_PROTOCOL_BY_HANDLE_PROTOCOL); mov rcx, [rsp+64] # get rootfs # Get rootfs push rdx # allocate stack for rootdir mov rdx, rsp # arg2 = &rootdir push rax # allocate shadow stack space for UEFI function push rax # allocate shadow stack space for UEFI function call [rcx+8] # rootfs->open_volume(rootfs, &rootdir) mov r14, [rsp+16] # save &rootdir # Open file for writing push rdx # allocate stack for fout mov rdx, rsp # arg2 = &fout push 0 # arg5 = 0 push 7 # to get 0x8000000000000003 we set the rightmost 3 bits pop r9 # and then do right rotation by 1 ror r9, 1 # arg4 = EFI_FILE_MODE_CREATE| EFI_FILE_MODE_WRITE | EFI_FILE_MODE_READ mov r8, r13 # arg3 = out mov rcx, r14 # arg1 = rootdir push rax # allocate shadow stack space for UEFI function push rax # allocate shadow stack space for UEFI function push rax # allocate shadow stack space for UEFI function push rax # allocate shadow stack space for UEFI function call [rcx+8] # rootdir->open() mov r13, [rsp+40] # get fout # Open file for reading push rdx # allocate stack for fin mov rdx, rsp # arg2 = &fin push 1 # arg5 = EFI_FILE_READ_ONLY push 1 # prepare to set arg4 to EFI_FILE_MODE_READ pop r9 # arg4 = EFI_FILE_MODE_READ mov r8, r12 # arg3 = in mov rcx, r14 # arg1 = rootdir push rax # allocate shadow stack space for UEFI function push rax # allocate shadow stack space for UEFI function push rax # allocate shadow stack space for UEFI function push rax # allocate shadow stack space for UEFI function call [rcx+8] # rootdir->open() mov r12, [rsp+40] # get fin # Our flag for byte processing push -1 pop r15 # r15 = -1 # temp storage for the sum xor r14d, r14d # r14 = 0 loop: # Read a byte call read_byte # process byte call hex # Deal with -1 values test rax, rax jl loop # deal with toggle test r15, r15 jge print # process first byte of pair mov r14, rax xor r15d, r15d # r15 = 0 jmp loop # process second byte of pair print: # update the sum and store in output shl r14, 4 add rax, r14 # flip the toggle push -1 pop r15 # r15 = -1 call write_byte jmp loop hex: # Purge Comment Lines (#) cmp rax, 35 je purge_comment # Purge Comment Lines (;) cmp rax, 59 je purge_comment # deal all ascii less than 0 cmp rax, 48 jl ascii_other # deal with 0-9 cmp rax, 58 jl ascii_num # deal with all ascii less than A cmp rax, 65 jl ascii_other # deal with A-F cmp rax, 71 jl ascii_high # deal with all ascii less than a cmp rax, 97 jl ascii_other # deal with a-f cmp rax, 103 jl ascii_low # The rest that remains needs to be ignored jmp ascii_other purge_comment: # Read a byte call read_byte # Loop if not LF (works for CR/LF and LF/CR endings too) cmp rax, 10 jne purge_comment # Otherwise return -1 push -1 pop rax # rax = -1 ret ascii_num: sub rax, 48 ret ascii_low: sub rax, 87 ret ascii_high: sub rax, 55 ret ascii_other: push -1 pop rax # rax = -1 ret terminate: push rbx # allocate stack mov rcx, r12 # arg1 = fin call [rcx+16] # fin->close() mov rcx, r13 # arg1 = fin call [rcx+16] # fout->close() abort: # used for debugging only mov rsp, rbp # restore stack ret # return to UEFI read_byte: mov rcx, r12 # arg1 = fin push 1 # size = 1 mov rdx, rsp # arg2 = &size push rbx # allocate stack mov r8, rsp # arg3 = &input push rax # allocate shadow stack space for UEFI function push rax # allocate shadow stack space for UEFI function push rax # allocate shadow stack space for UEFI function call [rcx+32] # fin->read() pop rax # deallocate stack pop rax # deallocate stack pop rax # deallocate stack pop rax # save input to rax pop rbx # save size to rbx # If the file ended (0 bytes read) terminate test rbx, rbx # if size == 0 je terminate # then we are done ret # return # Writes byte stored in al write_byte: mov rcx, r13 # arg1 = fout push 1 # size = 1 mov rdx, rsp # arg2 = &size push rax # allocate stack mov r8, rsp # arg3 = &output push rax # allocate shadow stack space for UEFI function push rax # allocate shadow stack space for UEFI function push rax # allocate shadow stack space for UEFI function call [rcx+40] # fout->write() add rsp, 40 # deallocate stack ret # return .data # Protocol GUIDs LOADED_IMAGE_PROTOCOL: .long 0x5b1b31a1 .short 0x9562 .short 0x11d2 .byte 0x8e, 0x3f, 0x00, 0xa0, 0xc9, 0x69, 0x72, 0x3b SIMPLE_FS_PROTOCOL: .long 0x0964e5b22 .short 0x6459 .short 0x11d2 .byte 0x8e, 0x39, 0x00, 0xa0, 0xc9, 0x69, 0x72, 0x3b