On Thu, Sep 15, 2022 at 8:04 PM Chao Peng <chao.p.peng@xxxxxxxxxxxxxxx> wrote:
>
> From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
>
> KVM can use memfd-provided memory for guest memory. For normal userspace
> accessible memory, KVM userspace (e.g. QEMU) mmaps the memfd into its
> virtual address space and then tells KVM to use the virtual address to
> setup the mapping in the secondary page table (e.g. EPT).
>
> With confidential computing technologies like Intel TDX, the
> memfd-provided memory may be encrypted with special key for special
> software domain (e.g. KVM guest) and is not expected to be directly
> accessed by userspace. Precisely, userspace access to such encrypted
> memory may lead to host crash so it should be prevented.
>
> This patch introduces userspace inaccessible memfd (created with
> MFD_INACCESSIBLE). Its memory is inaccessible from userspace through
> ordinary MMU access (e.g. read/write/mmap) but can be accessed via
> in-kernel interface so KVM can directly interact with core-mm without
> the need to map the memory into KVM userspace.
>
> It provides semantics required for KVM guest private(encrypted) memory
> support that a file descriptor with this flag set is going to be used as
> the source of guest memory in confidential computing environments such
> as Intel TDX/AMD SEV.
>
> KVM userspace is still in charge of the lifecycle of the memfd. It
> should pass the opened fd to KVM. KVM uses the kernel APIs newly added
> in this patch to obtain the physical memory address and then populate
> the secondary page table entries.
>
> The userspace inaccessible memfd can be fallocate-ed and hole-punched
> from userspace. When hole-punching happens, KVM can get notified through
> inaccessible_notifier it then gets chance to remove any mapped entries
> of the range in the secondary page tables.
>
> The userspace inaccessible memfd itself is implemented as a shim layer
> on top of real memory file systems like tmpfs/hugetlbfs but this patch
> only implemented tmpfs. The allocated memory is currently marked as
> unmovable and unevictable, this is required for current confidential
> usage. But in future this might be changed.
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> Signed-off-by: Chao Peng <chao.p.peng@xxxxxxxxxxxxxxx>
> ---
> include/linux/memfd.h | 24 ++++
> include/uapi/linux/magic.h | 1 +
> include/uapi/linux/memfd.h | 1 +
> mm/Makefile | 2 +-
> mm/memfd.c | 25 ++++-
> mm/memfd_inaccessible.c | 219 +++++++++++++++++++++++++++++++++++++
> 6 files changed, 270 insertions(+), 2 deletions(-)
> create mode 100644 mm/memfd_inaccessible.c
>
> diff --git a/include/linux/memfd.h b/include/linux/memfd.h
> index 4f1600413f91..334ddff08377 100644
> --- a/include/linux/memfd.h
> +++ b/include/linux/memfd.h
> @@ -3,6 +3,7 @@
> #define __LINUX_MEMFD_H
>
> #include <linux/file.h>
> +#include <linux/pfn_t.h>
>
> #ifdef CONFIG_MEMFD_CREATE
> extern long memfd_fcntl(struct file *file, unsigned int cmd, unsigned long arg);
> @@ -13,4 +14,27 @@ static inline long memfd_fcntl(struct file *f, unsigned int c, unsigned long a)
> }
> #endif
>
> +struct inaccessible_notifier;
> +
> +struct inaccessible_notifier_ops {
> + void (*invalidate)(struct inaccessible_notifier *notifier,
> + pgoff_t start, pgoff_t end);
> +};
> +
> +struct inaccessible_notifier {
> + struct list_head list;
> + const struct inaccessible_notifier_ops *ops;
> +};
> +
> +void inaccessible_register_notifier(struct file *file,
> + struct inaccessible_notifier *notifier);
> +void inaccessible_unregister_notifier(struct file *file,
> + struct inaccessible_notifier *notifier);
> +
> +int inaccessible_get_pfn(struct file *file, pgoff_t offset, pfn_t *pfn,
> + int *order);
> +void inaccessible_put_pfn(struct file *file, pfn_t pfn);
> +
> +struct file *memfd_mkinaccessible(struct file *memfd);
> +
> #endif /* __LINUX_MEMFD_H */
> diff --git a/include/uapi/linux/magic.h b/include/uapi/linux/magic.h
> index 6325d1d0e90f..9d066be3d7e8 100644
> --- a/include/uapi/linux/magic.h
> +++ b/include/uapi/linux/magic.h
> @@ -101,5 +101,6 @@
> #define DMA_BUF_MAGIC 0x444d4142 /* "DMAB" */
> #define DEVMEM_MAGIC 0x454d444d /* "DMEM" */
> #define SECRETMEM_MAGIC 0x5345434d /* "SECM" */
> +#define INACCESSIBLE_MAGIC 0x494e4143 /* "INAC" */
>
> #endif /* __LINUX_MAGIC_H__ */
> diff --git a/include/uapi/linux/memfd.h b/include/uapi/linux/memfd.h
> index 7a8a26751c23..48750474b904 100644
> --- a/include/uapi/linux/memfd.h
> +++ b/include/uapi/linux/memfd.h
> @@ -8,6 +8,7 @@
> #define MFD_CLOEXEC 0x0001U
> #define MFD_ALLOW_SEALING 0x0002U
> #define MFD_HUGETLB 0x0004U
> +#define MFD_INACCESSIBLE 0x0008U
>
> /*
> * Huge page size encoding when MFD_HUGETLB is specified, and a huge page
> diff --git a/mm/Makefile b/mm/Makefile
> index 9a564f836403..f82e5d4b4388 100644
> --- a/mm/Makefile
> +++ b/mm/Makefile
> @@ -126,7 +126,7 @@ obj-$(CONFIG_HARDENED_USERCOPY) += usercopy.o
> obj-$(CONFIG_PERCPU_STATS) += percpu-stats.o
> obj-$(CONFIG_ZONE_DEVICE) += memremap.o
> obj-$(CONFIG_HMM_MIRROR) += hmm.o
> -obj-$(CONFIG_MEMFD_CREATE) += memfd.o
> +obj-$(CONFIG_MEMFD_CREATE) += memfd.o memfd_inaccessible.o
> obj-$(CONFIG_MAPPING_DIRTY_HELPERS) += mapping_dirty_helpers.o
> obj-$(CONFIG_PTDUMP_CORE) += ptdump.o
> obj-$(CONFIG_PAGE_REPORTING) += page_reporting.o
> diff --git a/mm/memfd.c b/mm/memfd.c
> index 08f5f8304746..1853a90f49ff 100644
> --- a/mm/memfd.c
> +++ b/mm/memfd.c
> @@ -261,7 +261,8 @@ 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_ALL_FLAGS (MFD_CLOEXEC | MFD_ALLOW_SEALING | MFD_HUGETLB | \
> + MFD_INACCESSIBLE)
>
> SYSCALL_DEFINE2(memfd_create,
> const char __user *, uname,
> @@ -283,6 +284,14 @@ SYSCALL_DEFINE2(memfd_create,
> return -EINVAL;
> }
>
> + /* Disallow sealing when MFD_INACCESSIBLE is set. */
> + if ((flags & MFD_INACCESSIBLE) && (flags & MFD_ALLOW_SEALING))
> + return -EINVAL;
> +
> + /* TODO: add hugetlb support */
> + if ((flags & MFD_INACCESSIBLE) && (flags & MFD_HUGETLB))
> + return -EINVAL;
> +
> /* length includes terminating zero */
> len = strnlen_user(uname, MFD_NAME_MAX_LEN + 1);
> if (len <= 0)
> @@ -331,10 +340,24 @@ SYSCALL_DEFINE2(memfd_create,
> *file_seals &= ~F_SEAL_SEAL;
> }
>
> + if (flags & MFD_INACCESSIBLE) {
> + struct file *inaccessible_file;
> +
> + inaccessible_file = memfd_mkinaccessible(file);
> + if (IS_ERR(inaccessible_file)) {
> + error = PTR_ERR(inaccessible_file);
> + goto err_file;
> + }
> +
> + file = inaccessible_file;
> + }
> +
> fd_install(fd, file);
> kfree(name);
> return fd;
>
> +err_file:
> + fput(file);
> err_fd:
> put_unused_fd(fd);
> err_name:
> diff --git a/mm/memfd_inaccessible.c b/mm/memfd_inaccessible.c
> new file mode 100644
> index 000000000000..2d33cbdd9282
> --- /dev/null
> +++ b/mm/memfd_inaccessible.c
> @@ -0,0 +1,219 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#include "linux/sbitmap.h"
> +#include <linux/memfd.h>
> +#include <linux/pagemap.h>
> +#include <linux/pseudo_fs.h>
> +#include <linux/shmem_fs.h>
> +#include <uapi/linux/falloc.h>
> +#include <uapi/linux/magic.h>
> +
> +struct inaccessible_data {
> + struct mutex lock;
> + struct file *memfd;
> + struct list_head notifiers;
> +};
> +
> +static void inaccessible_notifier_invalidate(struct inaccessible_data *data,
> + pgoff_t start, pgoff_t end)
> +{
> + struct inaccessible_notifier *notifier;
> +
> + mutex_lock(&data->lock);
> + list_for_each_entry(notifier, &data->notifiers, list) {
> + notifier->ops->invalidate(notifier, start, end);
> + }
> + mutex_unlock(&data->lock);
> +}
> +
> +static int inaccessible_release(struct inode *inode, struct file *file)
> +{
> + struct inaccessible_data *data = inode->i_mapping->private_data;
> +
> + fput(data->memfd);
> + kfree(data);
> + return 0;
> +}
> +
> +static long inaccessible_fallocate(struct file *file, int mode,
> + loff_t offset, loff_t len)
> +{
> + struct inaccessible_data *data = file->f_mapping->private_data;
> + struct file *memfd = data->memfd;
> + int ret;
> +
> + if (mode & FALLOC_FL_PUNCH_HOLE) {
> + if (!PAGE_ALIGNED(offset) || !PAGE_ALIGNED(len))
> + return -EINVAL;
> + }
> +
> + ret = memfd->f_op->fallocate(memfd, mode, offset, len);
> + inaccessible_notifier_invalidate(data, offset, offset + len);
> + return ret;
> +}
> +
> +static const struct file_operations inaccessible_fops = {
> + .release = inaccessible_release,
> + .fallocate = inaccessible_fallocate,
> +};
> +
> +static int inaccessible_getattr(struct user_namespace *mnt_userns,
> + const struct path *path, struct kstat *stat,
> + u32 request_mask, unsigned int query_flags)
> +{
> + struct inode *inode = d_inode(path->dentry);
> + struct inaccessible_data *data = inode->i_mapping->private_data;
> + struct file *memfd = data->memfd;
> +
> + return memfd->f_inode->i_op->getattr(mnt_userns, path, stat,
> + request_mask, query_flags);
> +}
> +
> +static int inaccessible_setattr(struct user_namespace *mnt_userns,
> + struct dentry *dentry, struct iattr *attr)
> +{
> + struct inode *inode = d_inode(dentry);
> + struct inaccessible_data *data = inode->i_mapping->private_data;
> + struct file *memfd = data->memfd;
> + int ret;
> +
> + if (attr->ia_valid & ATTR_SIZE) {
> + if (memfd->f_inode->i_size)
> + return -EPERM;
> +
> + if (!PAGE_ALIGNED(attr->ia_size))
> + return -EINVAL;
> + }
> +
> + ret = memfd->f_inode->i_op->setattr(mnt_userns,
> + file_dentry(memfd), attr);
> + return ret;
> +}
> +
> +static const struct inode_operations inaccessible_iops = {
> + .getattr = inaccessible_getattr,
> + .setattr = inaccessible_setattr,
> +};
> +
> +static int inaccessible_init_fs_context(struct fs_context *fc)
> +{
> + if (!init_pseudo(fc, INACCESSIBLE_MAGIC))
> + return -ENOMEM;
> +
> + fc->s_iflags |= SB_I_NOEXEC;
> + return 0;
> +}
> +
> +static struct file_system_type inaccessible_fs = {
> + .owner = THIS_MODULE,
> + .name = "[inaccessible]",
> + .init_fs_context = inaccessible_init_fs_context,
> + .kill_sb = kill_anon_super,
> +};
> +
> +static struct vfsmount *inaccessible_mnt;
> +
> +static __init int inaccessible_init(void)
> +{
> + inaccessible_mnt = kern_mount(&inaccessible_fs);
> + if (IS_ERR(inaccessible_mnt))
> + return PTR_ERR(inaccessible_mnt);
> + return 0;
> +}
> +fs_initcall(inaccessible_init);
> +
> +struct file *memfd_mkinaccessible(struct file *memfd)
> +{
> + struct inaccessible_data *data;
> + struct address_space *mapping;
> + struct inode *inode;
> + struct file *file;
> +
> + data = kzalloc(sizeof(*data), GFP_KERNEL);
> + if (!data)
> + return ERR_PTR(-ENOMEM);
> +
> + data->memfd = memfd;
> + mutex_init(&data->lock);
> + INIT_LIST_HEAD(&data->notifiers);
> +
> + inode = alloc_anon_inode(inaccessible_mnt->mnt_sb);
> + if (IS_ERR(inode)) {
> + kfree(data);
> + return ERR_CAST(inode);
> + }
> +
> + inode->i_mode |= S_IFREG;
> + inode->i_op = &inaccessible_iops;
> + inode->i_mapping->private_data = data;
> +
> + file = alloc_file_pseudo(inode, inaccessible_mnt,
> + "[memfd:inaccessible]", O_RDWR,
> + &inaccessible_fops);
> + if (IS_ERR(file)) {
> + iput(inode);
> + kfree(data);
> + }
> +
> + file->f_flags |= O_LARGEFILE;
> +
> + mapping = memfd->f_mapping;
> + mapping_set_unevictable(mapping);
> + mapping_set_gfp_mask(mapping,
> + mapping_gfp_mask(mapping) & ~__GFP_MOVABLE);
> +
> + return file;
> +}
> +
> +void inaccessible_register_notifier(struct file *file,
> + struct inaccessible_notifier *notifier)
> +{
> + struct inaccessible_data *data = file->f_mapping->private_data;
> +
> + mutex_lock(&data->lock);
> + list_add(¬ifier->list, &data->notifiers);
> + mutex_unlock(&data->lock);
> +}
> +EXPORT_SYMBOL_GPL(inaccessible_register_notifier);
> +
> +void inaccessible_unregister_notifier(struct file *file,
> + struct inaccessible_notifier *notifier)
> +{
> + struct inaccessible_data *data = file->f_mapping->private_data;
> +
> + mutex_lock(&data->lock);
> + list_del(¬ifier->list);
> + mutex_unlock(&data->lock);
> +}
> +EXPORT_SYMBOL_GPL(inaccessible_unregister_notifier);
> +
> +int inaccessible_get_pfn(struct file *file, pgoff_t offset, pfn_t *pfn,
> + int *order)
> +{
> + struct inaccessible_data *data = file->f_mapping->private_data;
> + struct file *memfd = data->memfd;
> + struct page *page;
> + int ret;
> +
> + ret = shmem_getpage(file_inode(memfd), offset, &page, SGP_WRITE);
> + if (ret)
> + return ret;
> +
> + *pfn = page_to_pfn_t(page);
> + *order = thp_order(compound_head(page));
> + SetPageUptodate(page);
> + unlock_page(page);
> +
> + return 0;
> +}
> +EXPORT_SYMBOL_GPL(inaccessible_get_pfn);
> +
> +void inaccessible_put_pfn(struct file *file, pfn_t pfn)
> +{
> + struct page *page = pfn_t_to_page(pfn);
> +
> + if (WARN_ON_ONCE(!page))
> + return;
> +
> + put_page(page);
> +}
> +EXPORT_SYMBOL_GPL(inaccessible_put_pfn);
> --
> 2.25.1
>
In the context of userspace inaccessible memfd, what would be a
suggested way to enforce NUMA memory policy for physical memory
allocation? mbind[1] won't work here in absence of virtual address
range.
[1] https://github.com/chao-p/qemu/blob/privmem-v8/backends/hostmem.c#L382
