Author | Tokens | Token Proportion | Commits | Commit Proportion |
---|---|---|---|---|
David Herrmann | 965 | 90.61% | 1 | 12.50% |
Marc-André Lureau | 93 | 8.73% | 2 | 25.00% |
Jeff Xu | 3 | 0.28% | 1 | 12.50% |
Greg Kroah-Hartman | 1 | 0.09% | 1 | 12.50% |
Orson Zhai | 1 | 0.09% | 1 | 12.50% |
Michael Ellerman | 1 | 0.09% | 1 | 12.50% |
Saurav Shah | 1 | 0.09% | 1 | 12.50% |
Total | 1065 | 8 |
// SPDX-License-Identifier: GPL-2.0 /* * 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 <fcntl.h> #include <linux/memfd.h> #include <linux/types.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> #include "common.h" #define MFD_DEF_SIZE 8192 #define STACK_SIZE 65536 static size_t mfd_def_size = MFD_DEF_SIZE; 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) { char *zero; 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(); } if (argc >= 3) { if (!strcmp(argv[2], "hugetlbfs")) { unsigned long hpage_size = default_huge_page_size(); if (!hpage_size) { printf("Unable to determine huge page size\n"); abort(); } hugetlbfs_test = 1; mfd_def_size = hpage_size * 2; } else { printf("Unknown option: %s\n", argv[2]); abort(); } } zero = calloc(sizeof(*zero), mfd_def_size); /* 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 successful * 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"); free(zero); return 0; }
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