Initial version of sys_fork, sys_execve and sys_wait4.
It is not fully working yet, in particular child programs have broken initial stack and argv returns garbage.
This commit is contained in:
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4f2a62fa34
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ac13be4291
GPG Key ID:
0C0331D5228A3B62
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@ -10,29 +10,90 @@
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#include <unistd.h>
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#include <bootstrappable.h>
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#include "syscalls.c"
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#define MSR_EFER 0x60000080 + 0x60000000
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#define MSR_STAR 0x60000081 + 0x60000000
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#define MSR_LSTAR 0x60000082 + 0x60000000
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int extract_field(char *file_data, int position, int length)
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void* syscall_table;
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#define MAX_PROC 16
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#define MAX_MIB_PER_PROC 128
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#define MAX_SAVED_MIB 1024
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struct mem_block {
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void* address;
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int length;
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};
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struct process {
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struct process* parent;
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void* entry_point;
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void* brk;
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void* saved_brk;
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void* stack;
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void* saved_stack_pointer;
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void* memory;
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mem_block program;
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mem_block saved_stack;
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mem_block saved_memory;
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int child_exit_code;
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int forked;
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};
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struct process* current_process;
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void* _get_stack()
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{
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void *data;
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asm("mov_rax,rsp");
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}
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void* get_stack()
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{
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/* Adjust to stack depth of _get_stack function */
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return _get_stack() + (7 * sizeof(void*));
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}
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int extract_field(char* file_data, int position, int length)
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{
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void* data;
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memcpy(&data, file_data + position, length);
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return data;
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}
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void jump(void *start_address, int argc, char **argv, char **envp)
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int load_elf(FILE* file_in, struct process* current)
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{
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char *temp;
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for (; *envp != 0; envp += sizeof(char *))
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{
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int file_size = fseek(file_in, 0, SEEK_END);
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char* file_data = calloc(1, file_size + 0x1000); /* Allocate extra space in case application tries to use it */
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rewind(file_in);
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fread(file_data, 1, file_size, file_in);
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fclose(file_in);
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if ((file_data[0] != 0x7F) || (file_data[1] != 'E') ||
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(file_data[2] != 'L') || (file_data[3] != 'F')) {
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return 1;
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}
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current->program.address = file_data;
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current->program.length = file_size;
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return 0;
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}
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void* entry_point(char* raw_elf)
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{
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int entry_point = extract_field(raw_elf, 24, 8);
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int header_table = extract_field(raw_elf, 32, 8);
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int base_address = extract_field(raw_elf, header_table + 0x10, 8);
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return entry_point - base_address + raw_elf;
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}
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void jump(void* start_address, int argc, char** argv, char** envp)
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{
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current_process->stack = get_stack();
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char* temp;
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asm("push !0");
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for (; *envp != 0; envp += sizeof(char *)) {
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temp = *envp;
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asm("push_rax");
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}
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asm("push !0");
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unsigned i;
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for (i = argc; i > 0; i -= 1) {
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temp = argv[i];
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@ -48,6 +109,173 @@ void jump(void *start_address, int argc, char **argv, char **envp)
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);
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}
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int sys_read(int fd, char* buf, unsigned count, void, void, void)
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{
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return read(fd, buf, count);
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}
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int sys_write(int fd, char* buf, unsigned count, void, void, void)
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{
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return write(fd, buf, count);
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}
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int sys_open(char* name, int flag, int mode, void, void, void)
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{
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fputs(name, stderr);
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fputc('\n', stderr);
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return open(name, flag, mode);
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}
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int sys_close(int fd, void, void, void, void, void)
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{
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return close(fd);
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}
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int sys_lseek(int fd, int offset, int whence, void, void, void)
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{
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return lseek(fd, offset, whence);
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}
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int sys_brk(void* addr, void, void, void, void, void)
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{
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if (current_process->brk == NULL) {
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current_process->brk = calloc(1, MAX_MIB_PER_PROC * 1024 * 1024);
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if (current_process->brk == NULL) {
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return addr;
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}
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current_process->memory = current_process->brk;
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}
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if (addr == NULL) {
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return current_process->brk;
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}
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else {
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current_process->brk = addr;
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return current_process->brk;
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}
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}
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int sys_access(char* pathname, int mode, void, void, void, void)
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{
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return access(pathname, mode);
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}
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int sys_fork(void, void, void, void, void, void)
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{
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current_process->saved_brk = current_process->brk;
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current_process->saved_stack_pointer = get_stack();
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current_process->forked = TRUE;
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current_process->saved_stack.length = current_process->stack - current_process->saved_stack_pointer;
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current_process->saved_stack.address = malloc(current_process->saved_stack.length);
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memcpy(current_process->saved_stack.address, current_process->saved_stack_pointer, current_process->saved_stack.length);
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current_process->saved_memory.length = current_process->brk - current_process->memory;
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current_process->saved_memory.address = malloc(current_process->saved_memory.length);
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memcpy(current_process->saved_memory.address, current_process->memory, current_process->saved_memory.length);
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return 0; /* return as child */
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}
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int sys_execve(char* file_name, char** argv, char** envp, void, void, void)
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{
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if (current_process->forked) {
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struct process* new = calloc(1, sizeof(process));
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new->parent = current_process;
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current_process->forked = FALSE; /* fork was handled */
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current_process = new;
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}
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// else {
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// restore_stack(current_process->saved_stack); // FIXME
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// }
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FILE* file_in;
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file_in = fopen(file_name, "r");
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if (file_in == NULL) {
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return -1;
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}
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int rval;
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rval = load_elf(file_in, current_process);
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if (rval == 1) {
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return -1;
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}
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current_process->entry_point = entry_point(current_process->program.address);
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char** iter = argv;
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int argc;
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while(*iter != 0) {
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iter += sizeof(char *);
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argc += 1;
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}
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jump(current_process->entry_point, argc, argv, envp);
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}
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void sys_exit(unsigned value, void, void, void, void, void)
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{
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if (current_process->parent == NULL) {
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exit(value);
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}
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current_process->parent->child_exit_code = value;
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struct process* child = current_process;
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current_process = current_process->parent;
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// free(child); // FIXME
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memcpy(current_process->saved_stack_pointer, current_process->saved_stack.address, current_process->saved_stack.length);
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memcpy(current_process->memory, current_process->saved_memory.address, current_process->saved_memory.length);
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// free(current_process->saved_stack); // FIXME
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// free(current_process->saved_memory); // FIXME
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current_process->brk = current_process->saved_brk;
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current_process->saved_stack_pointer;
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/* Simulate return from sys_fork() */
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asm("mov_rsp,rax"
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"mov_rax, %1"
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"ret"
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);
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}
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int sys_wait4(int pid, int* status_ptr, int options)
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{
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*status_ptr = current_process->child_exit_code << 8;
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return 0;
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}
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int sys_getcwd(char* buf, int size, void, void, void, void)
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{
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return getcwd(buf, size);
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}
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int sys_chdir(char* path, void, void, void, void, void)
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{
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return chdir(path);
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}
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int sys_mkdir(char const* a, mode_t b, void, void, void, void)
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{
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return mkdir(a, b);
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}
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int sys_unlink(char* filename, void, void, void, void, void)
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{
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return unlink(filename);
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}
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void init_syscalls()
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{
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syscall_table = calloc(256, sizeof(void *));
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syscall_table[0] = sys_read;
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syscall_table[1] = sys_write;
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syscall_table[2] = sys_open;
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syscall_table[3] = sys_close;
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syscall_table[8] = sys_lseek;
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syscall_table[12] = sys_brk;
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syscall_table[21] = sys_access;
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syscall_table[57] = sys_fork;
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syscall_table[59] = sys_execve;
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syscall_table[60] = sys_exit;
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syscall_table[61] = sys_wait4;
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syscall_table[79] = sys_getcwd;
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syscall_table[80] = sys_chdir;
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syscall_table[83] = sys_mkdir;
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syscall_table[87] = sys_unlink;
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}
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void wrmsr(unsigned msr, int low, int high)
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{
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asm("lea_rcx,[rbp+DWORD] %-8"
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@ -77,7 +305,7 @@ ulong rdmsrl(unsigned msr)
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void _entry_syscall(long syscall, long arg1, long arg2, long arg3, long arg4, long arg5, long arg6)
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{
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FUNCTION *process_syscall = syscall_table[syscall];
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FUNCTION process_syscall = syscall_table[syscall];
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if(process_syscall != NULL) {
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return process_syscall(arg1, arg2, arg3, arg4, arg5, arg6);
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}
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@ -132,7 +360,7 @@ void entry_syscall()
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asm("jmp_rcx");
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}
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int main(int argc, char **argv, char **envp)
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int main(int argc, char** argv, char** envp)
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{
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if (argc < 2) {
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fputs("Usage: ", stderr);
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@ -141,29 +369,22 @@ int main(int argc, char **argv, char **envp)
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exit(1);
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}
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FILE *file_in = fopen(argv[1], "r");
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FILE* file_in = fopen(argv[1], "r");
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if (file_in == NULL) {
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fputs("Error opening input file.\n", stderr);
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exit(2);
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}
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/* Load binary into memory */
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int file_size = fseek(file_in, 0, SEEK_END);
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char *file_data = calloc(file_size + 0x1000); /* Allocate extra space in case application tries to use it */
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rewind(file_in);
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fread(file_data, 1, file_size, file_in);
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fclose(file_in);
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current_process = calloc(1, sizeof(process));
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if ((file_data[0] != 0x7F) || (file_data[1] != 'E') ||
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(file_data[2] != 'L') || (file_data[3] != 'F')) {
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/* Load binary into memory */
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int rval = load_elf(file_in, current_process);
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if (rval == 1) {
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fputs("ELF magic header was not found.\n", stderr);
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exit(3);
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}
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int entry_point = extract_field(file_data, 24, 8);
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int header_table = extract_field(file_data, 32, 8);
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int base_address = extract_field(file_data, header_table + 0x10, 8);
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void *start_address = entry_point - base_address + file_data;
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current_process->entry_point = entry_point(current_process->program.address);
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ulong msr_efer = rdmsrl(MSR_EFER);
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msr_efer |= 1; /* Enable syscalls */
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@ -175,7 +396,7 @@ int main(int argc, char **argv, char **envp)
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wrmsrl(MSR_LSTAR, entry_syscall);
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init_syscalls();
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jump(start_address, argc - 1, argv, envp);
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jump(current_process->entry_point, argc - 1, argv, envp);
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return 1;
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}
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@ -1,97 +0,0 @@
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/*
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* SPDX-FileCopyrightText: 2023 Andrius Štikonas <andrius@stikonas.eu>
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*
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* SPDX-License-Identifier: GPL-3.0-or-later
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*/
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void *syscall_table;
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void *_brk;
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int sys_read(int fd, char* buf, unsigned count, void, void, void)
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{
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return read(fd, buf, count);
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}
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int sys_write(int fd, char* buf, unsigned count, void, void, void)
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{
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return write(fd, buf, count);
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}
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int sys_open(char* name, int flag, int mode, void, void, void)
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{
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return open(name, flag, mode);
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}
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int sys_close(int fd, void, void, void, void, void)
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{
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return close(fd);
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}
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int sys_lseek(int fd, int offset, int whence, void, void, void)
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{
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return lseek(fd, offset, whence);
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}
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int sys_access(char* pathname, int mode, void, void, void, void)
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{
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return access(pathname, mode);
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}
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int sys_brk(void* addr, void, void, void, void, void)
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{
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if (_brk == NULL) {
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_brk = calloc(1, 128 * 1024 * 1024);
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if (_brk == NULL) {
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return addr;
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}
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}
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if (addr == NULL) {
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return _brk;
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}
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else {
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_brk = addr;
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return _brk;
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}
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}
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void sys_exit(unsigned value, void, void, void, void, void)
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{
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exit(value);
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}
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int sys_getcwd(char* buf, int size, void, void, void, void)
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{
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return getcwd(buf, size);
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}
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int sys_chdir(char* path, void, void, void, void, void)
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{
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return chdir(path);
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}
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int sys_mkdir(char const* a, mode_t b, void, void, void, void)
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{
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return mkdir(a, b);
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}
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int sys_unlink(char* filename, void, void, void, void, void)
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{
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return unlink(filename);
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}
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void init_syscalls()
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{
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syscall_table = calloc(256, sizeof(void*));
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syscall_table[0] = sys_read;
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syscall_table[1] = sys_write;
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syscall_table[2] = sys_open;
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syscall_table[3] = sys_close;
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syscall_table[8] = sys_lseek;
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syscall_table[12] = sys_brk;
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syscall_table[21] = sys_access;
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syscall_table[60] = sys_exit;
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syscall_table[79] = sys_getcwd;
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syscall_table[80] = sys_chdir;
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syscall_table[83] = sys_mkdir;
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syscall_table[87] = sys_unlink;
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}
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