On Mon, Jul 06, 2020 at 08:20:49PM +0300, Mike Rapoport wrote: > From: Mike Rapoport <[email protected]> > > Extend memfd_create() system call with the ability to create memory areas > visible only in the context of the owning process and not mapped not only > to other processes but in the kernel page tables as well. > > The user will create a file descriptor using the memfd_create system call. > The user than has to use ioctl() to define the desired protection mode for > the memory associated with that file descriptor and only when the mode is > set it is possible to mmap() the memory. For instance, the following > exapmple will create an uncached mapping (error handling is omitted): > > fd = memfd_create("secret", MFD_SECRET);
I'm not convinced that it belong to memfd. You don't share anything with memfd, but the syscall. > ioctl(fd, MFD_SECRET_UNCACHED); > ftruncate(fd. MAP_SIZE); Mix of tabs and spaces? > ptr = mmap(NULL, MAP_SIZE, PROT_READ | PROT_WRITE, MAP_SHARED, > fd, 0); > > Signed-off-by: Mike Rapoport <[email protected]> > --- > include/linux/memfd.h | 9 ++ > include/uapi/linux/magic.h | 1 + > include/uapi/linux/memfd.h | 6 + > mm/Kconfig | 3 + > mm/Makefile | 1 + > mm/memfd.c | 10 +- > mm/secretmem.c | 247 +++++++++++++++++++++++++++++++++++++ > 7 files changed, 275 insertions(+), 2 deletions(-) > create mode 100644 mm/secretmem.c > > diff --git a/include/linux/memfd.h b/include/linux/memfd.h > index 4f1600413f91..d3ca7285f51a 100644 > --- a/include/linux/memfd.h > +++ b/include/linux/memfd.h > @@ -13,4 +13,13 @@ static inline long memfd_fcntl(struct file *f, unsigned > int c, unsigned long a) > } > #endif > > +#ifdef CONFIG_MEMFD_SECRETMEM > +extern struct file *secretmem_file_create(const char *name, unsigned int > flags); > +#else > +static inline struct file *secretmem_file_create(const char *name, unsigned > int flags) > +{ > + return ERR_PTR(-EINVAL); > +} > +#endif > + > #endif /* __LINUX_MEMFD_H */ > diff --git a/include/uapi/linux/magic.h b/include/uapi/linux/magic.h > index f3956fc11de6..35687dcb1a42 100644 > --- a/include/uapi/linux/magic.h > +++ b/include/uapi/linux/magic.h > @@ -97,5 +97,6 @@ > #define DEVMEM_MAGIC 0x454d444d /* "DMEM" */ > #define Z3FOLD_MAGIC 0x33 > #define PPC_CMM_MAGIC 0xc7571590 > +#define SECRETMEM_MAGIC 0x5345434d /* "SECM" */ > > #endif /* __LINUX_MAGIC_H__ */ > diff --git a/include/uapi/linux/memfd.h b/include/uapi/linux/memfd.h > index 7a8a26751c23..3320a79b638d 100644 > --- a/include/uapi/linux/memfd.h > +++ b/include/uapi/linux/memfd.h > @@ -8,6 +8,12 @@ > #define MFD_CLOEXEC 0x0001U > #define MFD_ALLOW_SEALING 0x0002U > #define MFD_HUGETLB 0x0004U > +#define MFD_SECRET 0x0008U > + > +/* ioctls for secret memory */ > +#define MFD_SECRET_IOCTL '-' > +#define MFD_SECRET_EXCLUSIVE _IOW(MFD_SECRET_IOCTL, 0x13, unsigned long) > +#define MFD_SECRET_UNCACHED _IOW(MFD_SECRET_IOCTL, 0x14, unsigned long) > > /* > * Huge page size encoding when MFD_HUGETLB is specified, and a huge page > diff --git a/mm/Kconfig b/mm/Kconfig > index f2104cc0d35c..20dfcc54cc7a 100644 > --- a/mm/Kconfig > +++ b/mm/Kconfig > @@ -872,4 +872,7 @@ config ARCH_HAS_HUGEPD > config MAPPING_DIRTY_HELPERS > bool > > +config MEMFD_SECRETMEM > + def_bool MEMFD_CREATE && ARCH_HAS_SET_DIRECT_MAP > + > endmenu > diff --git a/mm/Makefile b/mm/Makefile > index 6e9d46b2efc9..a9459c8a655a 100644 > --- a/mm/Makefile > +++ b/mm/Makefile > @@ -121,3 +121,4 @@ obj-$(CONFIG_MEMFD_CREATE) += memfd.o > obj-$(CONFIG_MAPPING_DIRTY_HELPERS) += mapping_dirty_helpers.o > obj-$(CONFIG_PTDUMP_CORE) += ptdump.o > obj-$(CONFIG_PAGE_REPORTING) += page_reporting.o > +obj-$(CONFIG_MEMFD_SECRETMEM) += secretmem.o > diff --git a/mm/memfd.c b/mm/memfd.c > index 2647c898990c..3e1cc37e0389 100644 > --- a/mm/memfd.c > +++ b/mm/memfd.c > @@ -245,7 +245,8 @@ long memfd_fcntl(struct file *file, unsigned int cmd, > unsigned long arg) > #define MFD_NAME_PREFIX_LEN (sizeof(MFD_NAME_PREFIX) - 1) > #define MFD_NAME_MAX_LEN (NAME_MAX - MFD_NAME_PREFIX_LEN) > > -#define MFD_ALL_FLAGS (MFD_CLOEXEC | MFD_ALLOW_SEALING | MFD_HUGETLB) > +#define MFD_SECRET_MASK (MFD_CLOEXEC | MFD_SECRET) > +#define MFD_ALL_FLAGS (MFD_CLOEXEC | MFD_ALLOW_SEALING | MFD_HUGETLB | > MFD_SECRET) > > SYSCALL_DEFINE2(memfd_create, > const char __user *, uname, > @@ -257,6 +258,9 @@ SYSCALL_DEFINE2(memfd_create, > char *name; > long len; > > + if (flags & ~(unsigned int)MFD_SECRET_MASK) > + return -EINVAL; > + Didn't you just broke MFD_ALLOW_SEALING and MFD_HUGETLB with this? I guess the check has to be under 'if (flags & MFD_SECRET) {' check, no? And (unsigned int) case looks redundant to me. > if (!(flags & MFD_HUGETLB)) { > if (flags & ~(unsigned int)MFD_ALL_FLAGS) > return -EINVAL; > @@ -296,7 +300,9 @@ SYSCALL_DEFINE2(memfd_create, > goto err_name; > } > > - if (flags & MFD_HUGETLB) { > + if (flags & MFD_SECRET) { > + file = secretmem_file_create(name, flags); > + } else if (flags & MFD_HUGETLB) { > struct user_struct *user = NULL; > > file = hugetlb_file_setup(name, 0, VM_NORESERVE, &user, > diff --git a/mm/secretmem.c b/mm/secretmem.c > new file mode 100644 > index 000000000000..df8f8c958cc2 > --- /dev/null > +++ b/mm/secretmem.c > @@ -0,0 +1,247 @@ > +// SPDX-License-Identifier: GPL-2.0 > +#include <linux/mm.h> > +#include <linux/fs.h> > +#include <linux/mount.h> > +#include <linux/memfd.h> > +#include <linux/printk.h> > +#include <linux/pagemap.h> > +#include <linux/pseudo_fs.h> > +#include <linux/set_memory.h> > +#include <linux/sched/signal.h> > + > +#include <uapi/linux/memfd.h> > +#include <uapi/linux/magic.h> > + > +#include <asm/tlbflush.h> > + > +#include "internal.h" > + > +#undef pr_fmt > +#define pr_fmt(fmt) "secretmem: " fmt > + > +#define SECRETMEM_EXCLUSIVE 0x1 > +#define SECRETMEM_UNCACHED 0x2 > + > +struct secretmem_ctx { > + unsigned int mode; > +}; > + > +static struct page *secretmem_alloc_page(gfp_t gfp) > +{ > + /* > + * FIXME: use a cache of large pages to reduce the direct map > + * fragmentation > + */ > + return alloc_page(gfp); > +} > + > +static vm_fault_t secretmem_fault(struct vm_fault *vmf) > +{ > + struct address_space *mapping = vmf->vma->vm_file->f_mapping; > + struct inode *inode = file_inode(vmf->vma->vm_file); > + pgoff_t offset = vmf->pgoff; > + unsigned long addr; > + struct page *page; > + int ret = 0; > + > + if (((loff_t)vmf->pgoff << PAGE_SHIFT) >= i_size_read(inode)) > + return vmf_error(-EINVAL); > + > + page = find_get_entry(mapping, offset); > + if (!page) { > + page = secretmem_alloc_page(vmf->gfp_mask); > + if (!page) > + return vmf_error(-ENOMEM); > + > + ret = add_to_page_cache_lru(page, mapping, offset, > vmf->gfp_mask); > + if (unlikely(ret)) > + goto err_put_page; What the reason to add it to LRU? These pages never evictable. Do we have some PageLRU() check that needs to be satisfied or what? > + > + ret = set_direct_map_invalid_noflush(page); > + if (ret) > + goto err_del_page_cache; > + > + addr = (unsigned long)page_address(page); > + flush_tlb_kernel_range(addr, addr + PAGE_SIZE); > + > + __SetPageUptodate(page); > + > + ret = VM_FAULT_LOCKED; > + } > + > + vmf->page = page; > + return ret; > + > +err_del_page_cache: > + delete_from_page_cache(page); > +err_put_page: > + put_page(page); > + return vmf_error(ret); > +} > + > +static const struct vm_operations_struct secretmem_vm_ops = { > + .fault = secretmem_fault, > +}; > + > +static int secretmem_mmap(struct file *file, struct vm_area_struct *vma) > +{ > + struct secretmem_ctx *ctx = file->private_data; > + unsigned long mode = ctx->mode; > + unsigned long len = vma->vm_end - vma->vm_start; > + > + if (!mode) > + return -EINVAL; > + > + if (mlock_future_check(vma->vm_mm, vma->vm_flags | VM_LOCKED, len)) > + return -EAGAIN; > + > + switch (mode) { > + case SECRETMEM_UNCACHED: > + vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot); > + fallthrough; > + case SECRETMEM_EXCLUSIVE: > + vma->vm_ops = &secretmem_vm_ops; > + break; > + default: > + return -EINVAL; > + } > + > + vma->vm_flags |= VM_LOCKED; > + > + return 0; > +} > + > +static long secretmem_ioctl(struct file *file, unsigned cmd, unsigned long > arg) > +{ > + struct secretmem_ctx *ctx = file->private_data; > + unsigned long mode = ctx->mode; > + > + if (mode) > + return -EINVAL; > + > + switch (cmd) { > + case MFD_SECRET_EXCLUSIVE: > + mode = SECRETMEM_EXCLUSIVE; > + break; > + case MFD_SECRET_UNCACHED: > + mode = SECRETMEM_UNCACHED; > + break; > + default: > + return -EINVAL; > + } > + > + ctx->mode = mode; > + > + return 0; > +} > + > +const struct file_operations secretmem_fops = { > + .mmap = secretmem_mmap, > + .unlocked_ioctl = secretmem_ioctl, > + .compat_ioctl = secretmem_ioctl, > +}; > + > +static bool secretmem_isolate_page(struct page *page, isolate_mode_t mode) > +{ > + return false; > +} > + > +static int secretmem_migratepage(struct address_space *mapping, > + struct page *newpage, struct page *page, > + enum migrate_mode mode) > +{ > + return -EBUSY; > +} > + > +static void secretmem_freepage(struct page *page) > +{ > + set_direct_map_default_noflush(page); > +} > + > +static const struct address_space_operations secretmem_aops = { > + .freepage = secretmem_freepage, > + .migratepage = secretmem_migratepage, > + .isolate_page = secretmem_isolate_page, > +}; > + > +static struct vfsmount *secretmem_mnt; > + > +struct file *secretmem_file_create(const char *name, unsigned int flags) > +{ > + struct inode *inode = alloc_anon_inode(secretmem_mnt->mnt_sb); > + struct file *file = ERR_PTR(-ENOMEM); > + struct secretmem_ctx *ctx; > + > + if (IS_ERR(inode)) > + return ERR_CAST(inode); > + > + ctx = kzalloc(sizeof(*ctx), GFP_KERNEL); > + if (!ctx) > + goto err_free_inode; > + > + file = alloc_file_pseudo(inode, secretmem_mnt, "secretmem", > + O_RDWR, &secretmem_fops); > + if (IS_ERR(file)) > + goto err_free_ctx; > + > + mapping_set_unevictable(inode->i_mapping); > + > + inode->i_mapping->private_data = ctx; > + inode->i_mapping->a_ops = &secretmem_aops; > + > + /* pretend we are a normal file with zero size */ > + inode->i_mode |= S_IFREG; > + inode->i_size = 0; > + > + file->private_data = ctx; > + > + return file; > + > +err_free_ctx: > + kfree(ctx); > +err_free_inode: > + iput(inode); > + return file; > +} > + > +static void secretmem_evict_inode(struct inode *inode) > +{ > + struct secretmem_ctx *ctx = inode->i_private; > + > + truncate_inode_pages_final(&inode->i_data); > + clear_inode(inode); > + kfree(ctx); > +} > + > +static const struct super_operations secretmem_super_ops = { > + .evict_inode = secretmem_evict_inode, > +}; > + > +static int secretmem_init_fs_context(struct fs_context *fc) > +{ > + struct pseudo_fs_context *ctx = init_pseudo(fc, SECRETMEM_MAGIC); > + > + if (!ctx) > + return -ENOMEM; > + ctx->ops = &secretmem_super_ops; > + > + return 0; > +} > + > +static struct file_system_type secretmem_fs = { > + .name = "secretmem", > + .init_fs_context = secretmem_init_fs_context, > + .kill_sb = kill_anon_super, > +}; > + > +static int secretmem_init(void) > +{ > + int ret = 0; > + > + secretmem_mnt = kern_mount(&secretmem_fs); > + if (IS_ERR(secretmem_mnt)) > + ret = PTR_ERR(secretmem_mnt); > + > + return ret; > +} > +fs_initcall(secretmem_init); > -- > 2.26.2 > -- Kirill A. Shutemov
