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Detect volume down key combo for safe mode

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It is possible that a module is breaking the device so bad that zygote
cannot even be started. In this case, system_server cannot start and
detect the safe mode key combo, set the persist property, and reboot.

Also on old Android versions, the system directly goes to safe mode
after detecting a key combo without rebooting, defeating the purpose of
Magisk's safe mode protection if we only check for the persist property.

Directly adding key combo check natively in magiskd allows us to enter
Magisk safe mode before the system is even aware of it.
This commit is contained in:
topjohnwu
2020-05-19 04:53:16 -07:00
parent 3c04dab472
commit e02e46d0fc
4 changed files with 96 additions and 48 deletions
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57
native/jni/core/bootstages.cpp
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@@ -1,11 +1,7 @@
#include <sys/mount.h>
#include <sys/wait.h>
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <string.h>
#include <dirent.h>
#include <sys/sysmacros.h>
#include <linux/input.h>
#include <libgen.h>
#include <vector>
#include <string>
@@ -220,6 +216,53 @@ static void collect_logs(bool reset) {
});
}
#define test_bit(bit, array) (array[bit / 8] & (1 << (bit % 8)))
static bool check_key_combo() {
uint8_t bitmask[(KEY_MAX + 1) / 8];
vector<int> events;
constexpr char name[] = "/dev/.ev";
// First collect candidate events that accepts volume down
for (int minor = 64; minor < 96; ++minor) {
if (xmknod(name, S_IFCHR | 0444, makedev(13, minor)))
continue;
int fd = open(name, O_RDONLY | O_CLOEXEC);
unlink(name);
if (fd < 0)
continue;
memset(bitmask, 0, sizeof(bitmask));
ioctl(fd, EVIOCGBIT(EV_KEY, sizeof(bitmask)), bitmask);
if (test_bit(KEY_VOLUMEDOWN, bitmask))
events.push_back(fd);
else
close(fd);
}
if (events.empty())
return false;
run_finally fin([&]{ std::for_each(events.begin(), events.end(), close); });
// Check if volume down key is held continuously for more than 3 seconds
for (int i = 0; i < 300; ++i) {
bool pressed = false;
for (const int &fd : events) {
memset(bitmask, 0, sizeof(bitmask));
ioctl(fd, EVIOCGKEY(sizeof(bitmask)), bitmask);
if (test_bit(KEY_VOLUMEDOWN, bitmask)) {
pressed = true;
break;
}
}
if (!pressed)
return false;
// Check every 10ms
usleep(10000);
}
LOGD("KEY_VOLUMEDOWN detected: enter safe mode\n");
return true;
}
/****************
* Entry points *
****************/
@@ -260,7 +303,7 @@ void post_fs_data(int client) {
goto unblock_init;
}
if (getprop("persist.sys.safemode", true) == "1") {
if (getprop("persist.sys.safemode", true) == "1" || check_key_combo()) {
safe_mode = true;
// Disable all modules and magiskhide so next boot will be clean
foreach_modules("disable");