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MaxsTechReview
f27d0b006f
Wine asks for userfaultfd with the i386 syscall number on arm64, so it never gets one and falls back to mprotect and a SIGSEGV per first write, which under proot is a ptrace stop each time. libblsession hands it the real userfaultfd and, where Android refuses the PAGEMAP_SCAN ioctl, answers it from /proc/self/pagemap and UFFDIO_WRITEPROTECT.
114 lines
3.9 KiB
C
114 lines
3.9 KiB
C
#define _GNU_SOURCE
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#include <errno.h>
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#include <fcntl.h>
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#include <linux/fs.h>
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#include <linux/userfaultfd.h>
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#include <stdint.h>
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#include <sys/ioctl.h>
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#include <sys/syscall.h>
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#include <unistd.h>
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#define WINE_ARM64_USERFAULTFD 374
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#define PM_UFFD_WP (1ULL << 57)
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#define PM_SWAP (1ULL << 62)
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#define PM_PRESENT (1ULL << 63)
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#if defined(PAGEMAP_SCAN) && defined(UFFD_USER_MODE_ONLY)
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static int ww_uffd = -1;
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static int scan_blocked;
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#endif
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__attribute__((visibility("hidden"))) int bl_writewatch_syscall(long number, const long *args, long (*real)(long, ...), long *rc) {
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#if defined(__aarch64__) && defined(PAGEMAP_SCAN) && defined(UFFD_USER_MODE_ONLY)
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if (number != WINE_ARM64_USERFAULTFD || (args[0] & ~(long)(O_CLOEXEC | O_NONBLOCK | UFFD_USER_MODE_ONLY))) return 0;
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*rc = real(SYS_userfaultfd, args[0]);
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if (*rc >= 0) __atomic_store_n(&ww_uffd, (int)*rc, __ATOMIC_RELEASE);
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return 1;
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#else
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(void)number;
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(void)args;
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(void)real;
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(void)rc;
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return 0;
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#endif
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}
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#if defined(PAGEMAP_SCAN) && defined(UFFD_USER_MODE_ONLY)
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static int protect(int uffd, uint64_t start, uint64_t end) {
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if (start == end) return 0;
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struct uffdio_writeprotect wp = { .range = { start, end - start }, .mode = UFFDIO_WRITEPROTECT_MODE_WP };
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return ioctl(uffd, UFFDIO_WRITEPROTECT, &wp);
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}
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static long emulate_scan(int fd, int uffd, struct pm_scan_arg *a) {
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uint64_t page = (uint64_t)getpagesize();
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if (a->size < sizeof(*a) || (a->flags & ~(uint64_t)PM_SCAN_WP_MATCHING) || a->category_inverted || a->category_anyof_mask
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|| a->category_mask != PAGE_IS_WRITTEN || (a->return_mask & ~(uint64_t)PAGE_IS_WRITTEN) || a->end < a->start
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|| ((a->start | a->end) & (page - 1)) || (a->vec_len && !a->vec)) {
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errno = EINVAL;
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return -1;
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}
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struct page_region *vec = (struct page_region *)(uintptr_t)a->vec;
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uint64_t regions = 0, pages = 0, addr = a->start, wp_start = 0, wp_end = 0;
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uint64_t entries[512];
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int wp = (a->flags & PM_SCAN_WP_MATCHING) != 0;
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while (addr < a->end) {
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uint64_t want = (a->end - addr) / page;
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if (want > 512) want = 512;
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ssize_t got = pread(fd, entries, want * sizeof(entries[0]), (off_t)(addr / page * sizeof(entries[0])));
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if (got < 0) return -1;
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if (got == 0) break;
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for (uint64_t i = 0; i < (uint64_t)got / sizeof(entries[0]); i++, addr += page) {
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uint64_t e = entries[i];
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if (!(e & (PM_PRESENT | PM_SWAP)) || (e & PM_UFFD_WP)) continue;
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if (a->max_pages && pages >= a->max_pages) goto done;
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if (a->vec_len) {
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if (regions && vec[regions - 1].end == addr) {
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vec[regions - 1].end += page;
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} else {
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if (regions == a->vec_len) goto done;
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vec[regions].start = addr;
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vec[regions].end = addr + page;
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vec[regions].categories = PAGE_IS_WRITTEN & a->return_mask;
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regions++;
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}
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}
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pages++;
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if (!wp) continue;
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if (wp_end != addr) {
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if (protect(uffd, wp_start, wp_end) < 0) return -1;
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wp_start = addr;
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}
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wp_end = addr + page;
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}
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}
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done:
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if (wp && protect(uffd, wp_start, wp_end) < 0) return -1;
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a->walk_end = addr < a->end ? addr : a->end;
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return (long)regions;
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}
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#endif
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__attribute__((visibility("hidden"))) int bl_writewatch_ioctl(int (*real)(int, unsigned long, void *), int fd, unsigned long request,
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void *arg, int *rc) {
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#if defined(PAGEMAP_SCAN) && defined(UFFD_USER_MODE_ONLY)
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if (request != PAGEMAP_SCAN) return 0;
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int uffd = __atomic_load_n(&ww_uffd, __ATOMIC_ACQUIRE);
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if (uffd < 0) return 0;
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if (!__atomic_load_n(&scan_blocked, __ATOMIC_RELAXED)) {
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*rc = real(fd, request, arg);
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if (*rc >= 0 || errno != EACCES) return 1;
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__atomic_store_n(&scan_blocked, 1, __ATOMIC_RELAXED);
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}
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*rc = (int)emulate_scan(fd, uffd, (struct pm_scan_arg *)arg);
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return 1;
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#else
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(void)real;
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(void)fd;
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(void)request;
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(void)arg;
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(void)rc;
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return 0;
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#endif
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}
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