331 lines
7.5 KiB
C
331 lines
7.5 KiB
C
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// SPDX-License-Identifier: GPL-2.0
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/*
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* memfd GUP test-case
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* This tests memfd interactions with get_user_pages(). We require the
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* fuse_mnt.c program to provide a fake direct-IO FUSE mount-point for us. This
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* file-system delays _all_ reads by 1s and forces direct-IO. This means, any
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* read() on files in that file-system will pin the receive-buffer pages for at
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* least 1s via get_user_pages().
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*
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* We use this trick to race ADD_SEALS against a write on a memfd object. The
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* ADD_SEALS must fail if the memfd pages are still pinned. Note that we use
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* the read() syscall with our memory-mapped memfd object as receive buffer to
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* force the kernel to write into our memfd object.
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*/
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#define _GNU_SOURCE
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#define __EXPORTED_HEADERS__
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#include <errno.h>
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#include <inttypes.h>
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#include <limits.h>
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#include <linux/falloc.h>
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#include <linux/fcntl.h>
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#include <linux/memfd.h>
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#include <sched.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <signal.h>
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#include <string.h>
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#include <sys/mman.h>
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#include <sys/stat.h>
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#include <sys/syscall.h>
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#include <sys/wait.h>
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#include <unistd.h>
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#include "common.h"
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#define MFD_DEF_SIZE 8192
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#define STACK_SIZE 65536
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static size_t mfd_def_size = MFD_DEF_SIZE;
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static int mfd_assert_new(const char *name, loff_t sz, unsigned int flags)
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{
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int r, fd;
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fd = sys_memfd_create(name, flags);
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if (fd < 0) {
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printf("memfd_create(\"%s\", %u) failed: %m\n",
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name, flags);
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abort();
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}
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r = ftruncate(fd, sz);
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if (r < 0) {
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printf("ftruncate(%llu) failed: %m\n", (unsigned long long)sz);
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abort();
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}
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return fd;
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}
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static __u64 mfd_assert_get_seals(int fd)
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{
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long r;
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r = fcntl(fd, F_GET_SEALS);
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if (r < 0) {
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printf("GET_SEALS(%d) failed: %m\n", fd);
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abort();
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}
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return r;
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}
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static void mfd_assert_has_seals(int fd, __u64 seals)
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{
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__u64 s;
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s = mfd_assert_get_seals(fd);
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if (s != seals) {
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printf("%llu != %llu = GET_SEALS(%d)\n",
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(unsigned long long)seals, (unsigned long long)s, fd);
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abort();
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}
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}
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static void mfd_assert_add_seals(int fd, __u64 seals)
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{
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long r;
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__u64 s;
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s = mfd_assert_get_seals(fd);
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r = fcntl(fd, F_ADD_SEALS, seals);
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if (r < 0) {
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printf("ADD_SEALS(%d, %llu -> %llu) failed: %m\n",
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fd, (unsigned long long)s, (unsigned long long)seals);
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abort();
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}
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}
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static int mfd_busy_add_seals(int fd, __u64 seals)
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{
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long r;
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__u64 s;
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r = fcntl(fd, F_GET_SEALS);
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if (r < 0)
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s = 0;
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else
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s = r;
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r = fcntl(fd, F_ADD_SEALS, seals);
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if (r < 0 && errno != EBUSY) {
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printf("ADD_SEALS(%d, %llu -> %llu) didn't fail as expected with EBUSY: %m\n",
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fd, (unsigned long long)s, (unsigned long long)seals);
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abort();
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}
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return r;
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}
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static void *mfd_assert_mmap_shared(int fd)
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{
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void *p;
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p = mmap(NULL,
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mfd_def_size,
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PROT_READ | PROT_WRITE,
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MAP_SHARED,
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fd,
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0);
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if (p == MAP_FAILED) {
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printf("mmap() failed: %m\n");
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abort();
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}
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return p;
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}
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static void *mfd_assert_mmap_private(int fd)
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{
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void *p;
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p = mmap(NULL,
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mfd_def_size,
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PROT_READ | PROT_WRITE,
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MAP_PRIVATE,
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fd,
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0);
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if (p == MAP_FAILED) {
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printf("mmap() failed: %m\n");
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abort();
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}
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return p;
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}
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static int global_mfd = -1;
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static void *global_p = NULL;
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static int sealing_thread_fn(void *arg)
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{
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int sig, r;
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/*
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* This thread first waits 200ms so any pending operation in the parent
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* is correctly started. After that, it tries to seal @global_mfd as
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* SEAL_WRITE. This _must_ fail as the parent thread has a read() into
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* that memory mapped object still ongoing.
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* We then wait one more second and try sealing again. This time it
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* must succeed as there shouldn't be anyone else pinning the pages.
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*/
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/* wait 200ms for FUSE-request to be active */
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usleep(200000);
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/* unmount mapping before sealing to avoid i_mmap_writable failures */
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munmap(global_p, mfd_def_size);
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/* Try sealing the global file; expect EBUSY or success. Current
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* kernels will never succeed, but in the future, kernels might
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* implement page-replacements or other fancy ways to avoid racing
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* writes. */
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r = mfd_busy_add_seals(global_mfd, F_SEAL_WRITE);
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if (r >= 0) {
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printf("HURRAY! This kernel fixed GUP races!\n");
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} else {
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/* wait 1s more so the FUSE-request is done */
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sleep(1);
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/* try sealing the global file again */
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mfd_assert_add_seals(global_mfd, F_SEAL_WRITE);
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}
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return 0;
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}
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static pid_t spawn_sealing_thread(void)
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{
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uint8_t *stack;
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pid_t pid;
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stack = malloc(STACK_SIZE);
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if (!stack) {
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printf("malloc(STACK_SIZE) failed: %m\n");
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abort();
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}
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pid = clone(sealing_thread_fn,
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stack + STACK_SIZE,
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SIGCHLD | CLONE_FILES | CLONE_FS | CLONE_VM,
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NULL);
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if (pid < 0) {
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printf("clone() failed: %m\n");
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abort();
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}
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return pid;
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}
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static void join_sealing_thread(pid_t pid)
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{
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waitpid(pid, NULL, 0);
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}
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int main(int argc, char **argv)
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{
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char *zero;
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int fd, mfd, r;
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void *p;
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int was_sealed;
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pid_t pid;
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if (argc < 2) {
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printf("error: please pass path to file in fuse_mnt mount-point\n");
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abort();
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}
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if (argc >= 3) {
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if (!strcmp(argv[2], "hugetlbfs")) {
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unsigned long hpage_size = default_huge_page_size();
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if (!hpage_size) {
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printf("Unable to determine huge page size\n");
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abort();
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}
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hugetlbfs_test = 1;
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mfd_def_size = hpage_size * 2;
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} else {
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printf("Unknown option: %s\n", argv[2]);
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abort();
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}
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}
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zero = calloc(sizeof(*zero), mfd_def_size);
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/* open FUSE memfd file for GUP testing */
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printf("opening: %s\n", argv[1]);
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fd = open(argv[1], O_RDONLY | O_CLOEXEC);
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if (fd < 0) {
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printf("cannot open(\"%s\"): %m\n", argv[1]);
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abort();
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}
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/* create new memfd-object */
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mfd = mfd_assert_new("kern_memfd_fuse",
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mfd_def_size,
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MFD_CLOEXEC | MFD_ALLOW_SEALING);
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/* mmap memfd-object for writing */
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p = mfd_assert_mmap_shared(mfd);
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/* pass mfd+mapping to a separate sealing-thread which tries to seal
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* the memfd objects with SEAL_WRITE while we write into it */
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global_mfd = mfd;
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global_p = p;
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pid = spawn_sealing_thread();
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/* Use read() on the FUSE file to read into our memory-mapped memfd
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* object. This races the other thread which tries to seal the
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* memfd-object.
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* If @fd is on the memfd-fake-FUSE-FS, the read() is delayed by 1s.
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* This guarantees that the receive-buffer is pinned for 1s until the
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* data is written into it. The racing ADD_SEALS should thus fail as
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* the pages are still pinned. */
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r = read(fd, p, mfd_def_size);
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if (r < 0) {
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printf("read() failed: %m\n");
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abort();
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} else if (!r) {
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printf("unexpected EOF on read()\n");
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abort();
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}
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was_sealed = mfd_assert_get_seals(mfd) & F_SEAL_WRITE;
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/* Wait for sealing-thread to finish and verify that it
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* successfully sealed the file after the second try. */
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join_sealing_thread(pid);
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mfd_assert_has_seals(mfd, F_SEAL_WRITE);
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/* *IF* the memfd-object was sealed at the time our read() returned,
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* then the kernel did a page-replacement or canceled the read() (or
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* whatever magic it did..). In that case, the memfd object is still
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* all zero.
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* In case the memfd-object was *not* sealed, the read() was successfull
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* and the memfd object must *not* be all zero.
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* Note that in real scenarios, there might be a mixture of both, but
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* in this test-cases, we have explicit 200ms delays which should be
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* enough to avoid any in-flight writes. */
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p = mfd_assert_mmap_private(mfd);
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if (was_sealed && memcmp(p, zero, mfd_def_size)) {
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printf("memfd sealed during read() but data not discarded\n");
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abort();
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} else if (!was_sealed && !memcmp(p, zero, mfd_def_size)) {
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printf("memfd sealed after read() but data discarded\n");
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abort();
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}
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close(mfd);
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close(fd);
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printf("fuse: DONE\n");
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free(zero);
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return 0;
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}
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