add yoga-bios-unlock code

.gitignore

@@ -0,0 +1 @@
+/yoga-bios-unlock

Makefile

@@ -0,0 +1,5 @@
+yoga-unlock:
+	${CC} -o ./yoga-bios-unlock ./src/yoga-bios-unlock.c -O2 -Wall
+
+clean:
+	rm ./yoga-bios-unlock

README.md

@@ -0,0 +1,24 @@
+# yoga-bios-unlock
+
+Based on FlyGoat's work to unlock the BIOS advanced menu documented [here](https://zhuanlan.zhihu.com/p/184982689)
+I wrote that tool to unlock my yoga laptop without using a proprietary software which is only available for Windows.
+
+I'd like to thank FlyGoat a lot for giving me the right direction on how to translate his guide into low-level functions
+provided by glibc.
+
+This tool will unlock the advanced menu in your Lenovo Yoga Slim 7 14ARE05.
+
+## Disclaimer
+
+This tool may eat your cat, burn your house or do anything else beside the expected task.
+So use it at your own risk and be aware that you're playing around with your BIOS which may end in a bricked device.
+
+> Since I am still waiting for the arrival of my Yoga laptop this is quiet untested!
+
+## Usage
+
+    git clone https://github.com/esno/yoga-bios-unlock.git
+    cd ./yoga-bios-unlock
+    make
+
+    su -c ./yoga-bios-unlock

src/yoga-bios-unlock.c

@@ -0,0 +1,121 @@
+#include <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+#include <sys/io.h>
+#include <sys/types.h>
+
+#define __DMI_PATH "/sys/class/dmi/id"
+
+#define __BIOS_VENDOR "LENOVO"
+#define __BIOS_VERSION "DMCN32WW"
+
+#define __BOARD_NAME "LNVNB161216"
+#define __BOARD_VENDOR "LENOVO"
+#define __BOARD_VERSION "SDK0J40709 WIN"
+
+#define __CHASSIS_VERSION "Yoga Slim 7 14ARE05"
+
+int check_dmi(const char *file, const char *value);
+int is_yoga(void);
+int read_sysfs(const char *file, char *buffer, int n);
+
+int check_dmi(const char *file, const char *value) {
+  int l = 128;
+  char buffer[l];
+
+  memset(buffer, 0, 128);
+  if (read_sysfs(file, buffer, l) < 0) {
+    fprintf(stderr, "cannot read /sys/class/dmi/id/%s\n", file);
+    return -1;
+  }
+
+  if (strcmp(value, buffer) != 0) {
+    fprintf(stderr, "%s does not match (expected: %s / got: %s)\n", file, value, buffer);
+    return -1;
+  }
+
+  return 0;
+}
+
+int is_yoga(void) {
+  int rc = 0;
+
+  if (check_dmi("bios_vendor", __BIOS_VENDOR) < 0)
+    rc = -1;
+  if (check_dmi("bios_version", __BIOS_VERSION) < 0)
+    rc = -2;
+  if (check_dmi("board_name", __BOARD_NAME) < 0)
+    rc = -3;
+  if (check_dmi("board_vendor", __BOARD_VENDOR) < 0)
+    rc = -4;
+  if (check_dmi("board_version", __BOARD_VERSION) < 0)
+    rc = -5;
+  if (check_dmi("chassis_version", __CHASSIS_VERSION) < 0)
+    rc = -6;
+
+  return rc;
+}
+
+int read_sysfs(const char *file, char *buffer, int n) {
+  int l = strlen(__DMI_PATH) + strlen(file) + 2;
+  char filename[l];
+  FILE *fd;
+  int c;
+
+  memset(filename, 0, l);
+  snprintf(filename, l, "%s/%s", __DMI_PATH, file);
+  fd = fopen(filename, "r");
+  if (fd == NULL)
+    return -1;
+
+  if ((c = fread(buffer, 1, n, fd)) < 0) {
+    if (feof(fd) == 0) {
+      fclose(fd);
+      return -2;
+    }
+  }
+
+  buffer[c - 1] = '\0';
+  fclose(fd);
+  return 0;
+}
+
+int main(int argc, const char **argv) {
+  char ack;
+
+  if (is_yoga() < 0) {
+    fprintf(stderr, "wrong device, aborting!\n");
+    return EXIT_FAILURE;
+  }
+
+  if (geteuid() != 0) {
+    fprintf(stderr, "Requires root privileges!\n");
+    return EXIT_FAILURE;
+  }
+
+  fprintf(stdout, "WARNING: use at your own risk!\n");
+  fprintf(stdout, "Agree? (y/Y) ");
+  scanf("%1s", &ack);
+  if (ack != 'y' && ack != 'Y') {
+    fprintf(stdout, "nothing to do here\n");
+    return EXIT_SUCCESS;
+  }
+
+  if (iopl(3) < 0) {
+    fprintf(stderr, "Can't set I/O privilege level (%s)\n", strerror(errno));
+    return EXIT_FAILURE;
+  }
+
+  if (ioperm(0x72, 2, 1) < 0) {
+    fprintf(stderr, "Can't set I/O permission (%s)\n", strerror(errno));
+    return EXIT_FAILURE;
+  }
+
+  outb_p(0xf7, 0x72);
+  outb_p(0x77, 0x73);
+
+  return EXIT_SUCCESS;
+}