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131ba72ee5
Hiding it from the whole x86 web helper got it past tier0 (message loop, BrowserCreated) but then Chromium trapped on the status descriptor it opened itself, now a memfd copy - which is the other reason the shim leaves the web helper alone. With BL_WEBHELPER_HIDE_TRACER=1 only opens called from libtier0_s.so get the copy; Chromium's get procfs.
104 lines
4.2 KiB
C
104 lines
4.2 KiB
C
/*
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* Ported from WinNative (maxjivi05, feature/wayland-gamescope, 2026-09-18/19), GPL-3.0, with names
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* changed to this project's. The reasoning below is the original author's.
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*
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* The adjustments a session's opens need.
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*
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* O_NOATIME on the game library: the user's games are bound in from shared storage, which Android
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* serves over FUSE with every file owned by its media provider rather than by the app. O_NOATIME
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* is reserved for a file's owner, so the kernel refuses such an open outright with EPERM. The
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* Steam client opens every content file it reads that way, and treats the refusal as the file
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* being unreadable or missing: a validation reports corrupt or missing files and an update is
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* cancelled. The flag only asks the filesystem to skip an access-time update; the open is retried
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* without it. Every other refusal is passed through untouched, and a file the process may open
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* with the flag still is.
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*
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* The kernel's trace marker: tracefs is world-writable here, so the client's tier0 opens
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* /sys/kernel/tracing/trace_marker at startup - three times over, once per module that profiles -
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* and writes a "[%s] tgid=%d begin_ctx=%lld" line for every scope it enters. Nothing in the
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* session reads those markers, and they are one more thing that can land in the wrong file when
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* a descriptor number changes hands (tracer.c has the cause). They have been found appended to an
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* app manifest, which the client then cannot parse, to a download's state file, and to content
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* chunks, which it quarantines as corrupt. Refused the descriptor, tier0 writes nothing at all and
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* has nothing to lose.
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*
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* A process status is served without the container's tracer in it; see tracer.c.
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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 <fcntl.h>
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#include <stdarg.h>
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#include <stddef.h>
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#include <string.h>
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#include <sys/types.h>
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int bl_status_without_tracer(const char *path, int flags, const void *caller) __attribute__((visibility("hidden")));
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int bl_writable_retry(int dirfd, const char *path, int flags) __attribute__((visibility("hidden")));
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static int retry_without_noatime(int fd, int flags) {
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return fd < 0 && errno == EPERM && (flags & O_NOATIME);
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}
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/* Both spellings tier0 tries, the debugfs one first. */
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static int is_trace_marker(const char *path) {
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return path != NULL
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&& (strcmp(path, "/sys/kernel/tracing/trace_marker") == 0
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|| strcmp(path, "/sys/kernel/debug/tracing/trace_marker") == 0);
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}
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int open(const char *path, int flags, ...) {
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static int (*real_open)(const char *, int, ...);
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va_list ap;
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mode_t mode;
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int fd;
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va_start(ap, flags);
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mode = va_arg(ap, mode_t);
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va_end(ap);
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if (is_trace_marker(path)) {
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errno = EACCES;
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return -1;
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}
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if ((fd = bl_status_without_tracer(path, flags, __builtin_return_address(0))) >= 0) return fd;
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if (real_open == NULL) real_open = dlsym(RTLD_NEXT, "open");
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if (real_open == NULL) {
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errno = ENOSYS;
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return -1;
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}
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fd = real_open(path, flags, mode);
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if (retry_without_noatime(fd, flags)) fd = real_open(path, flags & ~O_NOATIME, mode);
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/* A read-only file the Steam client rewrites (perms.c). */
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if (fd < 0 && bl_writable_retry(AT_FDCWD, path, flags)) fd = real_open(path, flags & ~O_NOATIME, mode);
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return fd;
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}
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int openat(int dirfd, const char *path, int flags, ...) {
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static int (*real_openat)(int, const char *, int, ...);
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va_list ap;
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mode_t mode;
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int fd;
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va_start(ap, flags);
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mode = va_arg(ap, mode_t);
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va_end(ap);
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if (is_trace_marker(path)) {
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errno = EACCES;
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return -1;
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}
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if ((fd = bl_status_without_tracer(path, flags, __builtin_return_address(0))) >= 0) return fd;
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if (real_openat == NULL) real_openat = dlsym(RTLD_NEXT, "openat");
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if (real_openat == NULL) {
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errno = ENOSYS;
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return -1;
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}
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fd = real_openat(dirfd, path, flags, mode);
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if (retry_without_noatime(fd, flags)) fd = real_openat(dirfd, path, flags & ~O_NOATIME, mode);
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if (fd < 0 && bl_writable_retry(dirfd, path, flags)) fd = real_openat(dirfd, path, flags & ~O_NOATIME, mode);
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return fd;
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}
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/* The runtime is 64-bit, so the large-file names are the same calls. */
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int open64(const char *path, int flags, ...) __attribute__((alias("open")));
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int openat64(int dirfd, const char *path, int flags, ...) __attribute__((alias("openat")));
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