/* * memfd.c * * Copyright (c) 2015 Red Hat, Inc. * * QEMU library functions on POSIX which are shared between QEMU and * the QEMU tools. * * Permission is hereby granted, free of charge, to any person obtaining a copy * of this software and associated documentation files (the "Software"), to deal * in the Software without restriction, including without limitation the rights * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell * copies of the Software, and to permit persons to whom the Software is * furnished to do so, subject to the following conditions: * * The above copyright notice and this permission notice shall be included in * all copies or substantial portions of the Software. * * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN * THE SOFTWARE. */ #include "qemu/osdep.h" #include "qapi/error.h" #include "qemu/memfd.h" #include "qemu/host-utils.h" #if defined CONFIG_LINUX && !defined CONFIG_MEMFD #include <sys/syscall.h> #include <asm/unistd.h> static int memfd_create(const char *name, unsigned int flags) { #ifdef __NR_memfd_create return syscall(__NR_memfd_create, name, flags); #else errno = ENOSYS; return -1; #endif } #endif int qemu_memfd_create(const char *name, size_t size, bool hugetlb, uint64_t hugetlbsize, unsigned int seals, Error **errp) { int htsize = hugetlbsize ? ctz64(hugetlbsize) : 0; if (htsize && 1ULL << htsize != hugetlbsize) { error_setg(errp, "Hugepage size must be a power of 2"); return -1; } htsize = htsize << MFD_HUGE_SHIFT; #ifdef CONFIG_LINUX int mfd = -1; unsigned int flags = MFD_CLOEXEC; if (seals) { flags |= MFD_ALLOW_SEALING; } if (hugetlb) { flags |= MFD_HUGETLB; flags |= htsize; } mfd = memfd_create(name, flags); if (mfd < 0) { error_setg_errno(errp, errno, "failed to create memfd with flags 0x%x", flags); goto err; } if (ftruncate(mfd, size) == -1) { error_setg_errno(errp, errno, "failed to resize memfd to %zu", size); goto err; } if (seals && fcntl(mfd, F_ADD_SEALS, seals) == -1) { error_setg_errno(errp, errno, "failed to add seals 0x%x", seals); goto err; } return mfd; err: if (mfd >= 0) { close(mfd); } #else error_setg_errno(errp, ENOSYS, "failed to create memfd"); #endif return -1; } /* * This is a best-effort helper for shared memory allocation, with * optional sealing. The helper will do his best to allocate using * memfd with sealing, but may fallback on other methods without * sealing. */ void *qemu_memfd_alloc(const char *name, size_t size, unsigned int seals, int *fd, Error **errp) { void *ptr; int mfd = qemu_memfd_create(name, size, false, 0, seals, NULL); /* some systems have memfd without sealing */ if (mfd == -1) { mfd = qemu_memfd_create(name, size, false, 0, 0, NULL); } if (mfd == -1) { const char *tmpdir = g_get_tmp_dir(); gchar *fname; fname = g_strdup_printf("%s/memfd-XXXXXX", tmpdir); mfd = mkstemp(fname); unlink(fname); g_free(fname); if (mfd == -1 || ftruncate(mfd, size) == -1) { goto err; } } ptr = mmap(0, size, PROT_READ | PROT_WRITE, MAP_SHARED, mfd, 0); if (ptr == MAP_FAILED) { goto err; } *fd = mfd; return ptr; err: error_setg_errno(errp, errno, "failed to allocate shared memory"); if (mfd >= 0) { close(mfd); } return NULL; } void qemu_memfd_free(void *ptr, size_t size, int fd) { if (ptr) { munmap(ptr, size); } if (fd != -1) { close(fd); } } enum { MEMFD_KO, MEMFD_OK, MEMFD_TODO }; /** * qemu_memfd_alloc_check(): * * Check if qemu_memfd_alloc() can allocate, including using a * fallback implementation when host doesn't support memfd. */ bool qemu_memfd_alloc_check(void) { static int memfd_check = MEMFD_TODO; if (memfd_check == MEMFD_TODO) { int fd; void *ptr; fd = -1; ptr = qemu_memfd_alloc("test", 4096, 0, &fd, NULL); memfd_check = ptr ? MEMFD_OK : MEMFD_KO; qemu_memfd_free(ptr, 4096, fd); } return memfd_check == MEMFD_OK; } /** * qemu_memfd_check(): * * Check if host supports memfd. */ bool qemu_memfd_check(unsigned int flags) { #ifdef CONFIG_LINUX int mfd = memfd_create("test", flags | MFD_CLOEXEC); if (mfd >= 0) { close(mfd); return true; } #endif return false; }