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https://github.com/Droid-Deck/DroidDeck.git
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maxjivi05
8a6877423e
Every Electron AppImage hung without a window or crashed at its first page. Four causes, each enough on its own: - The session preload's hooks found the real functions with dlsym(RTLD_NEXT). Before glibc 2.34 a thread's first dlsym callocs, and Chromium's PartitionAlloc calls syscall() from inside its first malloc: the allocator waited for itself. On older glibc (the x86 runtime's 2.31) next.c now walks the libraries after the preload with no allocation and picks each function's default version, as glibc 2.36 does; the old lookup handed realpath() and posix_spawn() their compat versions, and realpath(path, NULL) failed. arm64 keeps dlsym. - libpci's sysfs backend exits when /sys/bus/pci/devices is listable but a device's files are not (a RedMagic's PCIe root port), taking every Chromium GPU process with it. An empty directory is bound over it on devices where that happens. - FEX_OUTPUTLOG=stderr made FEX log to its own duplicate of descriptor 2. Chromium dup2()s its IPC socket onto that low number in each child it starts, then lists /proc/self/fd, which FEX logs into the socket. Empty, FEX writes to descriptor 2 itself. - The tracer preload served every /proc/<pid>/status as a memfd, which is open for writing. Chromium hands each renderer its status as a read-only file and checks that it is one. Only a process's own status (pid, tid, self, thread-self) is rewritten now.
68 lines
2.3 KiB
C
68 lines
2.3 KiB
C
/*
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* noexec.c: FEX runs an x86 program and its libraries where they lie, on noexec shared storage too.
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* FEX maps them with the guest's PROT_EXEC, which the kernel refuses for a file on a noexec mount,
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* but it never runs those pages itself - it runs its own translation of them - so a mapping or an
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* mprotect refused for that alone is made without PROT_EXEC. Only in FEX's own processes.
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*/
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#define _GNU_SOURCE
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#include <dlfcn.h>
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#include <errno.h>
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#include <string.h>
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#include <sys/mman.h>
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#include <sys/statvfs.h>
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#include <unistd.h>
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__attribute__((visibility("hidden"))) void *bl_next(const char *name);
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/* NOEXEC_TEST: tools/tests builds it for the host. */
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#if defined(__aarch64__) || defined(NOEXEC_TEST)
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static int in_fex(void) {
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static int known = -1;
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if (known < 0) {
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char exe[512];
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ssize_t n = readlink("/proc/self/exe", exe, sizeof exe - 1);
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exe[n > 0 ? n : 0] = 0;
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const char *name = strrchr(exe, '/');
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name = name ? name + 1 : exe;
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known = !strcmp(name, "FEX") || !strcmp(name, "FEXInterpreter") || !strcmp(name, "FEXLoader");
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}
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return known;
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}
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/* After an mmap failed (fsync.c's mmap asks): whether to map it again without PROT_EXEC. */
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__attribute__((visibility("hidden"))) int bl_noexec_retry(int prot, int flags, int fd) {
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int error = errno;
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struct statvfs vfs;
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int retry = (error == EACCES || error == EPERM) && (prot & PROT_EXEC) && fd >= 0 && !(flags & MAP_ANONYMOUS) &&
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in_fex() && fstatvfs(fd, &vfs) == 0 && (vfs.f_flag & ST_NOEXEC);
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errno = error;
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return retry;
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}
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static int (*real_mprotect)(void *, size_t, int);
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/* Looked up before anything runs: Wine calls mprotect from its signal handlers, where dlsym is unsafe. */
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__attribute__((constructor)) static void noexec_init(void) {
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real_mprotect = (int (*)(void *, size_t, int))bl_next("mprotect");
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}
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int mprotect(void *addr, size_t len, int prot) {
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if (!real_mprotect) noexec_init();
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int result = real_mprotect(addr, len, prot);
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if (result && errno == EACCES && (prot & PROT_EXEC) && in_fex()) {
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result = real_mprotect(addr, len, prot & ~PROT_EXEC);
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if (result) errno = EACCES;
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}
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return result;
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}
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#else
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__attribute__((visibility("hidden"))) int bl_noexec_retry(int prot, int flags, int fd) {
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(void)prot, (void)flags, (void)fd;
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return 0;
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}
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#endif
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