diff options
Diffstat (limited to 'memfd/fuse_test.c')
-rw-r--r-- | memfd/fuse_test.c | 311 |
1 files changed, 0 insertions, 311 deletions
diff --git a/memfd/fuse_test.c b/memfd/fuse_test.c deleted file mode 100644 index 67908b1..0000000 --- a/memfd/fuse_test.c +++ /dev/null @@ -1,311 +0,0 @@ -/* - * memfd GUP test-case - * This tests memfd interactions with get_user_pages(). We require the - * fuse_mnt.c program to provide a fake direct-IO FUSE mount-point for us. This - * file-system delays _all_ reads by 1s and forces direct-IO. This means, any - * read() on files in that file-system will pin the receive-buffer pages for at - * least 1s via get_user_pages(). - * - * We use this trick to race ADD_SEALS against a write on a memfd object. The - * ADD_SEALS must fail if the memfd pages are still pinned. Note that we use - * the read() syscall with our memory-mapped memfd object as receive buffer to - * force the kernel to write into our memfd object. - */ - -#define _GNU_SOURCE -#define __EXPORTED_HEADERS__ - -#include <errno.h> -#include <inttypes.h> -#include <limits.h> -#include <linux/falloc.h> -#include <linux/fcntl.h> -#include <linux/memfd.h> -#include <sched.h> -#include <stdio.h> -#include <stdlib.h> -#include <signal.h> -#include <string.h> -#include <sys/mman.h> -#include <sys/stat.h> -#include <sys/syscall.h> -#include <sys/wait.h> -#include <unistd.h> - -#define MFD_DEF_SIZE 8192 -#define STACK_SIZE 65535 - -static int sys_memfd_create(const char *name, - unsigned int flags) -{ - return syscall(__NR_memfd_create, name, flags); -} - -static int mfd_assert_new(const char *name, loff_t sz, unsigned int flags) -{ - int r, fd; - - fd = sys_memfd_create(name, flags); - if (fd < 0) { - printf("memfd_create(\"%s\", %u) failed: %m\n", - name, flags); - abort(); - } - - r = ftruncate(fd, sz); - if (r < 0) { - printf("ftruncate(%llu) failed: %m\n", (unsigned long long)sz); - abort(); - } - - return fd; -} - -static __u64 mfd_assert_get_seals(int fd) -{ - long r; - - r = fcntl(fd, F_GET_SEALS); - if (r < 0) { - printf("GET_SEALS(%d) failed: %m\n", fd); - abort(); - } - - return r; -} - -static void mfd_assert_has_seals(int fd, __u64 seals) -{ - __u64 s; - - s = mfd_assert_get_seals(fd); - if (s != seals) { - printf("%llu != %llu = GET_SEALS(%d)\n", - (unsigned long long)seals, (unsigned long long)s, fd); - abort(); - } -} - -static void mfd_assert_add_seals(int fd, __u64 seals) -{ - long r; - __u64 s; - - s = mfd_assert_get_seals(fd); - r = fcntl(fd, F_ADD_SEALS, seals); - if (r < 0) { - printf("ADD_SEALS(%d, %llu -> %llu) failed: %m\n", - fd, (unsigned long long)s, (unsigned long long)seals); - abort(); - } -} - -static int mfd_busy_add_seals(int fd, __u64 seals) -{ - long r; - __u64 s; - - r = fcntl(fd, F_GET_SEALS); - if (r < 0) - s = 0; - else - s = r; - - r = fcntl(fd, F_ADD_SEALS, seals); - if (r < 0 && errno != EBUSY) { - printf("ADD_SEALS(%d, %llu -> %llu) didn't fail as expected with EBUSY: %m\n", - fd, (unsigned long long)s, (unsigned long long)seals); - abort(); - } - - return r; -} - -static void *mfd_assert_mmap_shared(int fd) -{ - void *p; - - p = mmap(NULL, - MFD_DEF_SIZE, - PROT_READ | PROT_WRITE, - MAP_SHARED, - fd, - 0); - if (p == MAP_FAILED) { - printf("mmap() failed: %m\n"); - abort(); - } - - return p; -} - -static void *mfd_assert_mmap_private(int fd) -{ - void *p; - - p = mmap(NULL, - MFD_DEF_SIZE, - PROT_READ | PROT_WRITE, - MAP_PRIVATE, - fd, - 0); - if (p == MAP_FAILED) { - printf("mmap() failed: %m\n"); - abort(); - } - - return p; -} - -static int global_mfd = -1; -static void *global_p = NULL; - -static int sealing_thread_fn(void *arg) -{ - int sig, r; - - /* - * This thread first waits 200ms so any pending operation in the parent - * is correctly started. After that, it tries to seal @global_mfd as - * SEAL_WRITE. This _must_ fail as the parent thread has a read() into - * that memory mapped object still ongoing. - * We then wait one more second and try sealing again. This time it - * must succeed as there shouldn't be anyone else pinning the pages. - */ - - /* wait 200ms for FUSE-request to be active */ - usleep(200000); - - /* unmount mapping before sealing to avoid i_mmap_writable failures */ - munmap(global_p, MFD_DEF_SIZE); - - /* Try sealing the global file; expect EBUSY or success. Current - * kernels will never succeed, but in the future, kernels might - * implement page-replacements or other fancy ways to avoid racing - * writes. */ - r = mfd_busy_add_seals(global_mfd, F_SEAL_WRITE); - if (r >= 0) { - printf("HURRAY! This kernel fixed GUP races!\n"); - } else { - /* wait 1s more so the FUSE-request is done */ - sleep(1); - - /* try sealing the global file again */ - mfd_assert_add_seals(global_mfd, F_SEAL_WRITE); - } - - return 0; -} - -static pid_t spawn_sealing_thread(void) -{ - uint8_t *stack; - pid_t pid; - - stack = malloc(STACK_SIZE); - if (!stack) { - printf("malloc(STACK_SIZE) failed: %m\n"); - abort(); - } - - pid = clone(sealing_thread_fn, - stack + STACK_SIZE, - SIGCHLD | CLONE_FILES | CLONE_FS | CLONE_VM, - NULL); - if (pid < 0) { - printf("clone() failed: %m\n"); - abort(); - } - - return pid; -} - -static void join_sealing_thread(pid_t pid) -{ - waitpid(pid, NULL, 0); -} - -int main(int argc, char **argv) -{ - static const char zero[MFD_DEF_SIZE]; - int fd, mfd, r; - void *p; - int was_sealed; - pid_t pid; - - if (argc < 2) { - printf("error: please pass path to file in fuse_mnt mount-point\n"); - abort(); - } - - /* open FUSE memfd file for GUP testing */ - printf("opening: %s\n", argv[1]); - fd = open(argv[1], O_RDONLY | O_CLOEXEC); - if (fd < 0) { - printf("cannot open(\"%s\"): %m\n", argv[1]); - abort(); - } - - /* create new memfd-object */ - mfd = mfd_assert_new("kern_memfd_fuse", - MFD_DEF_SIZE, - MFD_CLOEXEC | MFD_ALLOW_SEALING); - - /* mmap memfd-object for writing */ - p = mfd_assert_mmap_shared(mfd); - - /* pass mfd+mapping to a separate sealing-thread which tries to seal - * the memfd objects with SEAL_WRITE while we write into it */ - global_mfd = mfd; - global_p = p; - pid = spawn_sealing_thread(); - - /* Use read() on the FUSE file to read into our memory-mapped memfd - * object. This races the other thread which tries to seal the - * memfd-object. - * If @fd is on the memfd-fake-FUSE-FS, the read() is delayed by 1s. - * This guarantees that the receive-buffer is pinned for 1s until the - * data is written into it. The racing ADD_SEALS should thus fail as - * the pages are still pinned. */ - r = read(fd, p, MFD_DEF_SIZE); - if (r < 0) { - printf("read() failed: %m\n"); - abort(); - } else if (!r) { - printf("unexpected EOF on read()\n"); - abort(); - } - - was_sealed = mfd_assert_get_seals(mfd) & F_SEAL_WRITE; - - /* Wait for sealing-thread to finish and verify that it - * successfully sealed the file after the second try. */ - join_sealing_thread(pid); - mfd_assert_has_seals(mfd, F_SEAL_WRITE); - - /* *IF* the memfd-object was sealed at the time our read() returned, - * then the kernel did a page-replacement or canceled the read() (or - * whatever magic it did..). In that case, the memfd object is still - * all zero. - * In case the memfd-object was *not* sealed, the read() was successfull - * and the memfd object must *not* be all zero. - * Note that in real scenarios, there might be a mixture of both, but - * in this test-cases, we have explicit 200ms delays which should be - * enough to avoid any in-flight writes. */ - - p = mfd_assert_mmap_private(mfd); - if (was_sealed && memcmp(p, zero, MFD_DEF_SIZE)) { - printf("memfd sealed during read() but data not discarded\n"); - abort(); - } else if (!was_sealed && !memcmp(p, zero, MFD_DEF_SIZE)) { - printf("memfd sealed after read() but data discarded\n"); - abort(); - } - - close(mfd); - close(fd); - - printf("fuse: DONE\n"); - - return 0; -} |