Date:   Thu, 11 Nov 2021 22:13:40 +0800
From:   Chao Peng <chao.p.peng@...ux.intel.com>
To:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
        qemu-devel@...gnu.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H . Peter Anvin" <hpa@...or.com>,
        Hugh Dickins <hughd@...gle.com>,
        Jeff Layton <jlayton@...nel.org>,
        "J . Bruce Fields" <bfields@...ldses.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Yu Zhang <yu.c.zhang@...ux.intel.com>,
        Chao Peng <chao.p.peng@...ux.intel.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        luto@...nel.org, john.ji@...el.com, susie.li@...el.com,
        jun.nakajima@...el.com, dave.hansen@...el.com, ak@...ux.intel.com,
        david@...hat.com
Subject: [RFC PATCH 1/6] mm: Add F_SEAL_GUEST to shmem/memfd

The new seal is only allowed if there's no pre-existing pages in the fd
and there's no existing mapping of the file. After the seal is set, no
read/write/mmap from userspace is allowed.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
Signed-off-by: Yu Zhang <yu.c.zhang@...ux.intel.com>
Signed-off-by: Chao Peng <chao.p.peng@...ux.intel.com>
---
 include/linux/memfd.h      |  22 +++++++
 include/linux/shmem_fs.h   |   9 +++
 include/uapi/linux/fcntl.h |   1 +
 mm/memfd.c                 |  34 +++++++++-
 mm/shmem.c                 | 127 ++++++++++++++++++++++++++++++++++++-
 5 files changed, 189 insertions(+), 4 deletions(-)

diff --git a/include/linux/memfd.h b/include/linux/memfd.h
index 4f1600413f91..ea213f5e3f95 100644
--- a/include/linux/memfd.h
+++ b/include/linux/memfd.h
@@ -4,13 +4,35 @@
 
 #include <linux/file.h>
 
+struct guest_ops {
+	void (*invalidate_page_range)(struct inode *inode, void *owner,
+				      pgoff_t start, pgoff_t end);
+};
+
+struct guest_mem_ops {
+	unsigned long (*get_lock_pfn)(struct inode *inode, pgoff_t offset,
+					int *page_level);
+	void (*put_unlock_pfn)(unsigned long pfn);
+
+};
+
 #ifdef CONFIG_MEMFD_CREATE
 extern long memfd_fcntl(struct file *file, unsigned int cmd, unsigned long arg);
+
+extern inline int memfd_register_guest(struct inode *inode, void *owner,
+				       const struct guest_ops *guest_ops,
+				       const struct guest_mem_ops **guest_mem_ops);
 #else
 static inline long memfd_fcntl(struct file *f, unsigned int c, unsigned long a)
 {
 	return -EINVAL;
 }
+static inline int memfd_register_guest(struct inode *inode, void *owner,
+				       const struct guest_ops *guest_ops,
+				       const struct guest_mem_ops **guest_mem_ops)
+{
+	return -EINVAL;
+}
 #endif
 
 #endif /* __LINUX_MEMFD_H */
diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h
index d82b6f396588..1b4c032680d5 100644
--- a/include/linux/shmem_fs.h
+++ b/include/linux/shmem_fs.h
@@ -12,6 +12,9 @@
 
 /* inode in-kernel data */
 
+struct guest_ops;
+struct guest_mem_ops;
+
 struct shmem_inode_info {
 	spinlock_t		lock;
 	unsigned int		seals;		/* shmem seals */
@@ -24,6 +27,8 @@ struct shmem_inode_info {
 	struct simple_xattrs	xattrs;		/* list of xattrs */
 	atomic_t		stop_eviction;	/* hold when working on inode */
 	struct inode		vfs_inode;
+	void			*guest_owner;
+	const struct guest_ops	*guest_ops;
 };
 
 struct shmem_sb_info {
@@ -90,6 +95,10 @@ extern unsigned long shmem_swap_usage(struct vm_area_struct *vma);
 extern unsigned long shmem_partial_swap_usage(struct address_space *mapping,
 						pgoff_t start, pgoff_t end);
 
+extern int shmem_register_guest(struct inode *inode, void *owner,
+				const struct guest_ops *guest_ops,
+				const struct guest_mem_ops **guest_mem_ops);
+
 /* Flag allocation requirements to shmem_getpage */
 enum sgp_type {
 	SGP_READ,	/* don't exceed i_size, don't allocate page */
diff --git a/include/uapi/linux/fcntl.h b/include/uapi/linux/fcntl.h
index 2f86b2ad6d7e..c79bc8572721 100644
--- a/include/uapi/linux/fcntl.h
+++ b/include/uapi/linux/fcntl.h
@@ -43,6 +43,7 @@
 #define F_SEAL_GROW	0x0004	/* prevent file from growing */
 #define F_SEAL_WRITE	0x0008	/* prevent writes */
 #define F_SEAL_FUTURE_WRITE	0x0010  /* prevent future writes while mapped */
+#define F_SEAL_GUEST		0x0020
 /* (1U << 31) is reserved for signed error codes */
 
 /*
diff --git a/mm/memfd.c b/mm/memfd.c
index 2647c898990c..5a34173f55f4 100644
--- a/mm/memfd.c
+++ b/mm/memfd.c
@@ -130,11 +130,26 @@ static unsigned int *memfd_file_seals_ptr(struct file *file)
 	return NULL;
 }
 
+int memfd_register_guest(struct inode *inode, void *owner,
+			 const struct guest_ops *guest_ops,
+			 const struct guest_mem_ops **guest_mem_ops)
+{
+	if (shmem_mapping(inode->i_mapping)) {
+		return shmem_register_guest(inode, owner,
+					    guest_ops, guest_mem_ops);
+	}
+
+	return -EINVAL;
+}
+
+EXPORT_SYMBOL_GPL(memfd_register_guest);
+
 #define F_ALL_SEALS (F_SEAL_SEAL | \
 		     F_SEAL_SHRINK | \
 		     F_SEAL_GROW | \
 		     F_SEAL_WRITE | \
-		     F_SEAL_FUTURE_WRITE)
+		     F_SEAL_FUTURE_WRITE | \
+		     F_SEAL_GUEST)
 
 static int memfd_add_seals(struct file *file, unsigned int seals)
 {
@@ -203,10 +218,27 @@ static int memfd_add_seals(struct file *file, unsigned int seals)
 		}
 	}
 
+	if (seals & F_SEAL_GUEST) {
+		i_mmap_lock_read(inode->i_mapping);
+
+		if (!RB_EMPTY_ROOT(&inode->i_mapping->i_mmap.rb_root)) {
+			error = -EBUSY;
+			goto unlock;
+		}
+
+		if (i_size_read(inode)) {
+			error = -EBUSY;
+			goto unlock;
+		}
+	}
+
 	*file_seals |= seals;
 	error = 0;
 
 unlock:
+	if (seals & F_SEAL_GUEST)
+		i_mmap_unlock_read(inode->i_mapping);
+
 	inode_unlock(inode);
 	return error;
 }
diff --git a/mm/shmem.c b/mm/shmem.c
index b2db4ed0fbc7..978c841c42c4 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -80,6 +80,7 @@ static struct vfsmount *shm_mnt;
 #include <linux/userfaultfd_k.h>
 #include <linux/rmap.h>
 #include <linux/uuid.h>
+#include <linux/memfd.h>
 
 #include <linux/uaccess.h>
 
@@ -883,6 +884,21 @@ static bool shmem_punch_compound(struct page *page, pgoff_t start, pgoff_t end)
 	return split_huge_page(page) >= 0;
 }
 
+static void guest_invalidate_page(struct inode *inode,
+				  struct page *page, pgoff_t start, pgoff_t end)
+{
+	struct shmem_inode_info *info = SHMEM_I(inode);
+
+	if (!info->guest_ops || !info->guest_ops->invalidate_page_range)
+		return;
+
+	start = max(start, page->index);
+	end = min(end, page->index + HPAGE_PMD_NR) - 1;
+
+	info->guest_ops->invalidate_page_range(inode, info->guest_owner,
+					       start, end);
+}
+
 /*
  * Remove range of pages and swap entries from page cache, and free them.
  * If !unfalloc, truncate or punch hole; if unfalloc, undo failed fallocate.
@@ -923,6 +939,8 @@ static void shmem_undo_range(struct inode *inode, loff_t lstart, loff_t lend,
 			}
 			index += thp_nr_pages(page) - 1;
 
+			guest_invalidate_page(inode, page, start, end);
+
 			if (!unfalloc || !PageUptodate(page))
 				truncate_inode_page(mapping, page);
 			unlock_page(page);
@@ -999,6 +1017,9 @@ static void shmem_undo_range(struct inode *inode, loff_t lstart, loff_t lend,
 					index--;
 					break;
 				}
+
+				guest_invalidate_page(inode, page, start, end);
+
 				VM_BUG_ON_PAGE(PageWriteback(page), page);
 				if (shmem_punch_compound(page, start, end))
 					truncate_inode_page(mapping, page);
@@ -1074,6 +1095,9 @@ static int shmem_setattr(struct user_namespace *mnt_userns,
 		    (newsize > oldsize && (info->seals & F_SEAL_GROW)))
 			return -EPERM;
 
+		if ((info->seals & F_SEAL_GUEST) && (newsize & ~PAGE_MASK))
+			return -EINVAL;
+
 		if (newsize != oldsize) {
 			error = shmem_reacct_size(SHMEM_I(inode)->flags,
 					oldsize, newsize);
@@ -1348,6 +1372,8 @@ static int shmem_writepage(struct page *page, struct writeback_control *wbc)
 		goto redirty;
 	if (!total_swap_pages)
 		goto redirty;
+	if (info->seals & F_SEAL_GUEST)
+		goto redirty;
 
 	/*
 	 * Our capabilities prevent regular writeback or sync from ever calling
@@ -2278,6 +2304,9 @@ static int shmem_mmap(struct file *file, struct vm_area_struct *vma)
 			vma->vm_flags &= ~(VM_MAYWRITE);
 	}
 
+	if (info->seals & F_SEAL_GUEST)
+		return -EPERM;
+
 	/* arm64 - allow memory tagging on RAM-based files */
 	vma->vm_flags |= VM_MTE_ALLOWED;
 
@@ -2519,12 +2548,14 @@ shmem_write_begin(struct file *file, struct address_space *mapping,
 	pgoff_t index = pos >> PAGE_SHIFT;
 
 	/* i_mutex is held by caller */
-	if (unlikely(info->seals & (F_SEAL_GROW |
-				   F_SEAL_WRITE | F_SEAL_FUTURE_WRITE))) {
+	if (unlikely(info->seals & (F_SEAL_GROW | F_SEAL_WRITE |
+				    F_SEAL_FUTURE_WRITE | F_SEAL_GUEST))) {
 		if (info->seals & (F_SEAL_WRITE | F_SEAL_FUTURE_WRITE))
 			return -EPERM;
 		if ((info->seals & F_SEAL_GROW) && pos + len > inode->i_size)
 			return -EPERM;
+		if (info->seals & F_SEAL_GUEST)
+			return -EPERM;
 	}
 
 	return shmem_getpage(inode, index, pagep, SGP_WRITE);
@@ -2598,6 +2629,20 @@ static ssize_t shmem_file_read_iter(struct kiocb *iocb, struct iov_iter *to)
 		end_index = i_size >> PAGE_SHIFT;
 		if (index > end_index)
 			break;
+
+		/*
+		 * inode_lock protects setting up seals as well as write to
+		 * i_size. Setting F_SEAL_GUEST only allowed with i_size == 0.
+		 *
+		 * Check F_SEAL_GUEST after i_size. It effectively serialize
+		 * read vs. setting F_SEAL_GUEST without taking inode_lock in
+		 * read path.
+		 */
+		if (SHMEM_I(inode)->seals & F_SEAL_GUEST) {
+			error = -EPERM;
+			break;
+		}
+
 		if (index == end_index) {
 			nr = i_size & ~PAGE_MASK;
 			if (nr <= offset)
@@ -2723,6 +2768,12 @@ static long shmem_fallocate(struct file *file, int mode, loff_t offset,
 			goto out;
 		}
 
+		if ((info->seals & F_SEAL_GUEST) &&
+		    (offset & ~PAGE_MASK || len & ~PAGE_MASK)) {
+			error = -EINVAL;
+			goto out;
+		}
+
 		shmem_falloc.waitq = &shmem_falloc_waitq;
 		shmem_falloc.start = (u64)unmap_start >> PAGE_SHIFT;
 		shmem_falloc.next = (unmap_end + 1) >> PAGE_SHIFT;
@@ -3806,6 +3857,20 @@ static void shmem_destroy_inodecache(void)
 	kmem_cache_destroy(shmem_inode_cachep);
 }
 
+#ifdef CONFIG_MIGRATION
+int shmem_migrate_page(struct address_space *mapping,
+		struct page *newpage, struct page *page,
+		enum migrate_mode mode)
+{
+	struct inode *inode = mapping->host;
+	struct shmem_inode_info *info = SHMEM_I(inode);
+
+	if (info->seals & F_SEAL_GUEST)
+		return -ENOTSUPP;
+	return migrate_page(mapping, newpage, page, mode);
+}
+#endif
+
 const struct address_space_operations shmem_aops = {
 	.writepage	= shmem_writepage,
 	.set_page_dirty	= __set_page_dirty_no_writeback,
@@ -3814,12 +3879,68 @@ const struct address_space_operations shmem_aops = {
 	.write_end	= shmem_write_end,
 #endif
 #ifdef CONFIG_MIGRATION
-	.migratepage	= migrate_page,
+	.migratepage	= shmem_migrate_page,
 #endif
 	.error_remove_page = generic_error_remove_page,
 };
 EXPORT_SYMBOL(shmem_aops);
 
+static unsigned long shmem_get_lock_pfn(struct inode *inode, pgoff_t offset,
+					int *page_level)
+{
+	struct page *page;
+	int ret;
+
+	ret = shmem_getpage(inode, offset, &page, SGP_WRITE);
+	if (ret)
+		return ret;
+
+	if (is_transparent_hugepage(page))
+		*page_level = PG_LEVEL_2M;
+	else
+		*page_level = PG_LEVEL_4K;
+
+	return page_to_pfn(page);
+}
+
+static void shmem_put_unlock_pfn(unsigned long pfn)
+{
+	struct page *page = pfn_to_page(pfn);
+
+	VM_BUG_ON_PAGE(!PageLocked(page), page);
+
+	set_page_dirty(page);
+	unlock_page(page);
+	put_page(page);
+}
+
+static const struct guest_mem_ops shmem_guest_ops = {
+	.get_lock_pfn = shmem_get_lock_pfn,
+	.put_unlock_pfn = shmem_put_unlock_pfn,
+};
+
+int shmem_register_guest(struct inode *inode, void *owner,
+			 const struct guest_ops *guest_ops,
+			 const struct guest_mem_ops **guest_mem_ops)
+{
+	struct shmem_inode_info *info = SHMEM_I(inode);
+
+	if (!owner)
+		return -EINVAL;
+
+	if (info->guest_owner) {
+		if (info->guest_owner == owner)
+			return 0;
+		else
+			return -EPERM;
+	}
+
+	info->guest_owner = owner;
+	info->guest_ops = guest_ops;
+	*guest_mem_ops = &shmem_guest_ops;
+	return 0;
+}
+
 static const struct file_operations shmem_file_operations = {
 	.mmap		= shmem_mmap,
 	.get_unmapped_area = shmem_get_unmapped_area,
-- 
2.17.1

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