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/** @file usermem.c
*
* @brief userspace r/w functions.
*
* @author Hanjie Wu (hanjiew)
* @bug No functional bugs
*/
#include <stdlib.h>
#include <string.h>
#include <common_kern.h>
#include <x86/asm.h>
#include <x86/seg.h>
#include <mm.h>
#include <paging.h>
#include <pts.h>
#include <sched.h>
/**
* @brief try to read a byte from userspace
* @param addr address
* @param output output byte if successful
* @return 0 on success, jump to usermem_fail on failure
*/
int try_read(va_t addr, char* output);
/**
* @brief try to write a byte to userspace
* @param addr address
* @param c byte to write
* @return 0 on success, jump to usermem_fail on failure
*/
int try_write(va_t addr, char c);
/**
* @brief tell the calling function the r/w failed
* @return -1
*/
int usermem_fail();
/**
* @brief setup fault handler before r/w
* @return old fault handler
*/
static reg_t usermem_setup() {
thread_t* current = get_current();
reg_t old_eip0 = current->eip0;
current->eip0 = (reg_t)usermem_fail;
if (current->process->pv != NULL) {
set_gs(SEGSEL_PV_DS);
} else {
set_gs(SEGSEL_USER_DS);
}
return old_eip0;
}
/**
* @brief restore old fault handler
* @param old_eip0 old fault handler
*/
static void usermem_finish(reg_t old_eip0) {
get_current()->eip0 = old_eip0;
}
int copy_from_user(va_t addr, int size, void* buf) {
reg_t old_eip0 = usermem_setup();
int i, result = 0;
for (i = 0; i < size; i++) {
if (try_read(addr + i, (char*)buf + i) != 0) {
result = -1;
break;
}
}
usermem_finish(old_eip0);
return result;
}
int copy_to_user(va_t addr, int size, void* buf) {
reg_t old_eip0 = usermem_setup();
int i, result = 0;
for (i = 0; i < size; i++) {
if (try_write(addr + i, *((char*)buf + i)) != 0) {
result = -1;
break;
}
}
usermem_finish(old_eip0);
return result;
}
char* copy_string_from_user(va_t addr, int maxlen) {
reg_t old_eip0 = usermem_setup();
int len = 0, buflen = 3 * sizeof(int);
char* buf = malloc(buflen);
char c;
if (buf == NULL) {
goto read_string_finished;
}
while (1) {
if (len >= maxlen || try_read(addr + len, &c) != 0) {
free(buf);
buf = NULL;
break;
}
buf[len++] = c;
if (c == '\0') {
break;
}
if (len >= buflen) {
buflen <<= 1;
char* result = realloc(buf, buflen);
if (result == NULL) {
free(buf);
buf = NULL;
break;
}
buf = result;
}
}
read_string_finished:
usermem_finish(old_eip0);
return buf;
}
int print_buf_from_user(pts_t* pts, va_t addr, int len) {
reg_t old_eip0 = usermem_setup();
int i, result = 0;
char c;
for (i = 0; i < len; i++) {
if (try_read(addr + i, &c) != 0) {
result = -1;
break;
}
pts_putbyte(pts, c);
}
usermem_finish(old_eip0);
return result;
}
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