[v9,2/5] mseal: add mseal syscall

diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index 77eb9b0e7685..abdf93951405 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -821,6 +821,7 @@  asmlinkage long sys_process_mrelease(int pidfd, unsigned int flags);
 asmlinkage long sys_remap_file_pages(unsigned long start, unsigned long size,
 			unsigned long prot, unsigned long pgoff,
 			unsigned long flags);
+asmlinkage long sys_mseal(unsigned long start, size_t len, unsigned long flags);
 asmlinkage long sys_mbind(unsigned long start, unsigned long len,
 				unsigned long mode,
 				const unsigned long __user *nmask,
diff --git a/mm/Makefile b/mm/Makefile
index e4b5b75aaec9..cbae83f74642 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -43,6 +43,10 @@  ifdef CONFIG_CROSS_MEMORY_ATTACH
 mmu-$(CONFIG_MMU)	+= process_vm_access.o
 endif
 
+ifdef CONFIG_64BIT
+mmu-$(CONFIG_MMU)	+= mseal.o
+endif
+
 obj-y			:= filemap.o mempool.o oom_kill.o fadvise.o \
 			   maccess.o page-writeback.o folio-compat.o \
 			   readahead.o swap.o truncate.o vmscan.o shrinker.o \
diff --git a/mm/internal.h b/mm/internal.h
index f309a010d50f..ca42acee3a3f 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -1221,6 +1221,43 @@  void __meminit __init_single_page(struct page *page, unsigned long pfn,
 unsigned long shrink_slab(gfp_t gfp_mask, int nid, struct mem_cgroup *memcg,
 			  int priority);
 
+#ifdef CONFIG_64BIT
+/* VM is sealed, in vm_flags */
+#define VM_SEALED	_BITUL(63)
+#endif
+
+#ifdef CONFIG_64BIT
+static inline int can_do_mseal(unsigned long flags)
+{
+	if (flags)
+		return -EINVAL;
+
+	return 0;
+}
+
+bool can_modify_mm(struct mm_struct *mm, unsigned long start,
+		unsigned long end);
+bool can_modify_mm_madv(struct mm_struct *mm, unsigned long start,
+		unsigned long end, int behavior);
+#else
+static inline int can_do_mseal(unsigned long flags)
+{
+	return -EPERM;
+}
+
+static inline bool can_modify_mm(struct mm_struct *mm, unsigned long start,
+		unsigned long end)
+{
+	return true;
+}
+
+static inline bool can_modify_mm_madv(struct mm_struct *mm, unsigned long start,
+		unsigned long end, int behavior)
+{
+	return true;
+}
+#endif
+
 #ifdef CONFIG_SHRINKER_DEBUG
 static inline __printf(2, 0) int shrinker_debugfs_name_alloc(
 			struct shrinker *shrinker, const char *fmt, va_list ap)
diff --git a/mm/madvise.c b/mm/madvise.c
index cfa5e7288261..8cd916a9ee1d 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -1394,6 +1394,7 @@  int madvise_set_anon_name(struct mm_struct *mm, unsigned long start,
  *  -EIO    - an I/O error occurred while paging in data.
  *  -EBADF  - map exists, but area maps something that isn't a file.
  *  -EAGAIN - a kernel resource was temporarily unavailable.
+ *  -EPERM  - memory is sealed.
  */
 int do_madvise(struct mm_struct *mm, unsigned long start, size_t len_in, int behavior)
 {
@@ -1437,10 +1438,21 @@  int do_madvise(struct mm_struct *mm, unsigned long start, size_t len_in, int beh
 	start = untagged_addr_remote(mm, start);
 	end = start + len;
 
+	/*
+	 * Check if the address range is sealed for do_madvise().
+	 * can_modify_mm_madv assumes we have acquired the lock on MM.
+	 */
+	if (!can_modify_mm_madv(mm, start, end, behavior)) {
+		error = -EPERM;
+		goto out;
+	}
+
 	blk_start_plug(&plug);
 	error = madvise_walk_vmas(mm, start, end, behavior,
 			madvise_vma_behavior);
 	blk_finish_plug(&plug);
+
+out:
 	if (write)
 		mmap_write_unlock(mm);
 	else
diff --git a/mm/mmap.c b/mm/mmap.c
index d89770eaab6b..d495fac95550 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1261,6 +1261,16 @@  unsigned long do_mmap(struct file *file, unsigned long addr,
 			return -EEXIST;
 	}
 
+	/*
+	 * addr is returned from get_unmapped_area,
+	 * There are two cases:
+	 * 1> MAP_FIXED == false
+	 *	unallocated memory, no need to check sealing.
+	 * 1> MAP_FIXED == true
+	 *	sealing is checked inside mmap_region when
+	 *	do_vmi_munmap is called.
+	 */
+
 	if (prot == PROT_EXEC) {
 		pkey = execute_only_pkey(mm);
 		if (pkey < 0)
@@ -2681,6 +2691,14 @@  int do_vmi_munmap(struct vma_iterator *vmi, struct mm_struct *mm,
 	if (end == start)
 		return -EINVAL;
 
+	/*
+	 * Check if memory is sealed before arch_unmap.
+	 * Prevent unmapping a sealed VMA.
+	 * can_modify_mm assumes we have acquired the lock on MM.
+	 */
+	if (!can_modify_mm(mm, start, end))
+		return -EPERM;
+
 	 /* arch_unmap() might do unmaps itself.  */
 	arch_unmap(mm, start, end);
 
@@ -2743,7 +2761,10 @@  unsigned long mmap_region(struct file *file, unsigned long addr,
 	}
 
 	/* Unmap any existing mapping in the area */
-	if (do_vmi_munmap(&vmi, mm, addr, len, uf, false))
+	error = do_vmi_munmap(&vmi, mm, addr, len, uf, false);
+	if (error == -EPERM)
+		return error;
+	else if (error)
 		return -ENOMEM;
 
 	/*
@@ -3104,6 +3125,14 @@  int do_vma_munmap(struct vma_iterator *vmi, struct vm_area_struct *vma,
 {
 	struct mm_struct *mm = vma->vm_mm;
 
+	/*
+	 * Check if memory is sealed before arch_unmap.
+	 * Prevent unmapping a sealed VMA.
+	 * can_modify_mm assumes we have acquired the lock on MM.
+	 */
+	if (!can_modify_mm(mm, start, end))
+		return -EPERM;
+
 	arch_unmap(mm, start, end);
 	return do_vmi_align_munmap(vmi, vma, mm, start, end, uf, unlock);
 }
diff --git a/mm/mprotect.c b/mm/mprotect.c
index 81991102f785..5f0f716bf4ae 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -32,6 +32,7 @@ 
 #include <linux/sched/sysctl.h>
 #include <linux/userfaultfd_k.h>
 #include <linux/memory-tiers.h>
+#include <uapi/linux/mman.h>
 #include <asm/cacheflush.h>
 #include <asm/mmu_context.h>
 #include <asm/tlbflush.h>
@@ -743,6 +744,15 @@  static int do_mprotect_pkey(unsigned long start, size_t len,
 		}
 	}
 
+	/*
+	 * checking if memory is sealed.
+	 * can_modify_mm assumes we have acquired the lock on MM.
+	 */
+	if (!can_modify_mm(current->mm, start, end)) {
+		error = -EPERM;
+		goto out;
+	}
+
 	prev = vma_prev(&vmi);
 	if (start > vma->vm_start)
 		prev = vma;
diff --git a/mm/mremap.c b/mm/mremap.c
index 38d98465f3d8..d69b438dcf83 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -902,7 +902,25 @@  static unsigned long mremap_to(unsigned long addr, unsigned long old_len,
 	if ((mm->map_count + 2) >= sysctl_max_map_count - 3)
 		return -ENOMEM;
 
+	/*
+	 * In mremap_to().
+	 * Move a VMA to another location, check if src addr is sealed.
+	 *
+	 * Place can_modify_mm here because mremap_to()
+	 * does its own checking for address range, and we only
+	 * check the sealing after passing those checks.
+	 *
+	 * can_modify_mm assumes we have acquired the lock on MM.
+	 */
+	if (!can_modify_mm(mm, addr, addr + old_len))
+		return -EPERM;
+
 	if (flags & MREMAP_FIXED) {
+		/*
+		 * In mremap_to().
+		 * VMA is moved to dst address, and munmap dst first.
+		 * do_munmap will check if dst is sealed.
+		 */
 		ret = do_munmap(mm, new_addr, new_len, uf_unmap_early);
 		if (ret)
 			goto out;
@@ -1061,6 +1079,19 @@  SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len,
 		goto out;
 	}
 
+	/*
+	 * Below is shrink/expand case (not mremap_to())
+	 * Check if src address is sealed, if so, reject.
+	 * In other words, prevent shrinking or expanding a sealed VMA.
+	 *
+	 * Place can_modify_mm here so we can keep the logic related to
+	 * shrink/expand together.
+	 */
+	if (!can_modify_mm(mm, addr, addr + old_len)) {
+		ret = -EPERM;
+		goto out;
+	}
+
 	/*
 	 * Always allow a shrinking remap: that just unmaps
 	 * the unnecessary pages..
diff --git a/mm/mseal.c b/mm/mseal.c
new file mode 100644
index 000000000000..daadac4b8125
--- /dev/null
+++ b/mm/mseal.c
@@ -0,0 +1,307 @@ 
+// SPDX-License-Identifier: GPL-2.0
+/*
+ *  Implement mseal() syscall.
+ *
+ *  Copyright (c) 2023,2024 Google, Inc.
+ *
+ *  Author: Jeff Xu <jeffxu@chromium.org>
+ */
+
+#include <linux/mempolicy.h>
+#include <linux/mman.h>
+#include <linux/mm.h>
+#include <linux/mm_inline.h>
+#include <linux/mmu_context.h>
+#include <linux/syscalls.h>
+#include <linux/sched.h>
+#include "internal.h"
+
+static inline bool vma_is_sealed(struct vm_area_struct *vma)
+{
+	return (vma->vm_flags & VM_SEALED);
+}
+
+static inline void set_vma_sealed(struct vm_area_struct *vma)
+{
+	vm_flags_set(vma, VM_SEALED);
+}
+
+/*
+ * check if a vma is sealed for modification.
+ * return true, if modification is allowed.
+ */
+static bool can_modify_vma(struct vm_area_struct *vma)
+{
+	if (vma_is_sealed(vma))
+		return false;
+
+	return true;
+}
+
+static bool is_madv_discard(int behavior)
+{
+	return	behavior &
+		(MADV_FREE | MADV_DONTNEED | MADV_DONTNEED_LOCKED |
+		 MADV_REMOVE | MADV_DONTFORK | MADV_WIPEONFORK);
+}
+
+static bool is_ro_anon(struct vm_area_struct *vma)
+{
+	/* check anonymous mapping. */
+	if (vma->vm_file || vma->vm_flags & VM_SHARED)
+		return false;
+
+	/*
+	 * check for non-writable:
+	 * PROT=RO or PKRU is not writeable.
+	 */
+	if (!(vma->vm_flags & VM_WRITE) ||
+		!arch_vma_access_permitted(vma, true, false, false))
+		return true;
+
+	return false;
+}
+
+/*
+ * Check if the vmas of a memory range are allowed to be modified.
+ * the memory ranger can have a gap (unallocated memory).
+ * return true, if it is allowed.
+ */
+bool can_modify_mm(struct mm_struct *mm, unsigned long start, unsigned long end)
+{
+	struct vm_area_struct *vma;
+
+	VMA_ITERATOR(vmi, mm, start);
+
+	/* going through each vma to check. */
+	for_each_vma_range(vmi, vma, end) {
+		if (!can_modify_vma(vma))
+			return false;
+	}
+
+	/* Allow by default. */
+	return true;
+}
+
+/*
+ * Check if the vmas of a memory range are allowed to be modified by madvise.
+ * the memory ranger can have a gap (unallocated memory).
+ * return true, if it is allowed.
+ */
+bool can_modify_mm_madv(struct mm_struct *mm, unsigned long start, unsigned long end,
+		int behavior)
+{
+	struct vm_area_struct *vma;
+
+	VMA_ITERATOR(vmi, mm, start);
+
+	if (!is_madv_discard(behavior))
+		return true;
+
+	/* going through each vma to check. */
+	for_each_vma_range(vmi, vma, end)
+		if (is_ro_anon(vma) && !can_modify_vma(vma))
+			return false;
+
+	/* Allow by default. */
+	return true;
+}
+
+static int mseal_fixup(struct vma_iterator *vmi, struct vm_area_struct *vma,
+		struct vm_area_struct **prev, unsigned long start,
+		unsigned long end, vm_flags_t newflags)
+{
+	int ret = 0;
+	vm_flags_t oldflags = vma->vm_flags;
+
+	if (newflags == oldflags)
+		goto out;
+
+	vma = vma_modify_flags(vmi, *prev, vma, start, end, newflags);
+	if (IS_ERR(vma)) {
+		ret = PTR_ERR(vma);
+		goto out;
+	}
+
+	set_vma_sealed(vma);
+out:
+	*prev = vma;
+	return ret;
+}
+
+/*
+ * Check for do_mseal:
+ * 1> start is part of a valid vma.
+ * 2> end is part of a valid vma.
+ * 3> No gap (unallocated address) between start and end.
+ * 4> map is sealable.
+ */
+static int check_mm_seal(unsigned long start, unsigned long end)
+{
+	struct vm_area_struct *vma;
+	unsigned long nstart = start;
+
+	VMA_ITERATOR(vmi, current->mm, start);
+
+	/* going through each vma to check. */
+	for_each_vma_range(vmi, vma, end) {
+		if (vma->vm_start > nstart)
+			/* unallocated memory found. */
+			return -ENOMEM;
+
+		if (vma->vm_end >= end)
+			return 0;
+
+		nstart = vma->vm_end;
+	}
+
+	return -ENOMEM;
+}
+
+/*
+ * Apply sealing.
+ */
+static int apply_mm_seal(unsigned long start, unsigned long end)
+{
+	unsigned long nstart;
+	struct vm_area_struct *vma, *prev;
+
+	VMA_ITERATOR(vmi, current->mm, start);
+
+	vma = vma_iter_load(&vmi);
+	/*
+	 * Note: check_mm_seal should already checked ENOMEM case.
+	 * so vma should not be null, same for the other ENOMEM cases.
+	 */
+	prev = vma_prev(&vmi);
+	if (start > vma->vm_start)
+		prev = vma;
+
+	nstart = start;
+	for_each_vma_range(vmi, vma, end) {
+		int error;
+		unsigned long tmp;
+		vm_flags_t newflags;
+
+		newflags = vma->vm_flags | VM_SEALED;
+		tmp = vma->vm_end;
+		if (tmp > end)
+			tmp = end;
+		error = mseal_fixup(&vmi, vma, &prev, nstart, tmp, newflags);
+		if (error)
+			return error;
+		nstart = vma_iter_end(&vmi);
+	}
+
+	return 0;
+}
+
+/*
+ * mseal(2) seals the VM's meta data from
+ * selected syscalls.
+ *
+ * addr/len: VM address range.
+ *
+ *  The address range by addr/len must meet:
+ *   start (addr) must be in a valid VMA.
+ *   end (addr + len) must be in a valid VMA.
+ *   no gap (unallocated memory) between start and end.
+ *   start (addr) must be page aligned.
+ *
+ *  len: len will be page aligned implicitly.
+ *
+ *   Below VMA operations are blocked after sealing.
+ *   1> Unmapping, moving to another location, and shrinking
+ *	the size, via munmap() and mremap(), can leave an empty
+ *	space, therefore can be replaced with a VMA with a new
+ *	set of attributes.
+ *   2> Moving or expanding a different vma into the current location,
+ *	via mremap().
+ *   3> Modifying a VMA via mmap(MAP_FIXED).
+ *   4> Size expansion, via mremap(), does not appear to pose any
+ *	specific risks to sealed VMAs. It is included anyway because
+ *	the use case is unclear. In any case, users can rely on
+ *	merging to expand a sealed VMA.
+ *   5> mprotect and pkey_mprotect.
+ *   6> Some destructive madvice() behavior (e.g. MADV_DONTNEED)
+ *      for anonymous memory, when users don't have write permission to the
+ *	memory. Those behaviors can alter region contents by discarding pages,
+ *	effectively a memset(0) for anonymous memory.
+ *
+ *  flags: reserved.
+ *
+ * return values:
+ *  zero: success.
+ *  -EINVAL:
+ *   invalid input flags.
+ *   start address is not page aligned.
+ *   Address arange (start + len) overflow.
+ *  -ENOMEM:
+ *   addr is not a valid address (not allocated).
+ *   end (start + len) is not a valid address.
+ *   a gap (unallocated memory) between start and end.
+ *  -EPERM:
+ *  - In 32 bit architecture, sealing is not supported.
+ * Note:
+ *  user can call mseal(2) multiple times, adding a seal on an
+ *  already sealed memory is a no-action (no error).
+ *
+ *  unseal() is not supported.
+ */
+static int do_mseal(unsigned long start, size_t len_in, unsigned long flags)
+{
+	size_t len;
+	int ret = 0;
+	unsigned long end;
+	struct mm_struct *mm = current->mm;
+
+	ret = can_do_mseal(flags);
+	if (ret)
+		return ret;
+
+	start = untagged_addr(start);
+	if (!PAGE_ALIGNED(start))
+		return -EINVAL;
+
+	len = PAGE_ALIGN(len_in);
+	/* Check to see whether len was rounded up from small -ve to zero. */
+	if (len_in && !len)
+		return -EINVAL;
+
+	end = start + len;
+	if (end < start)
+		return -EINVAL;
+
+	if (end == start)
+		return 0;
+
+	if (mmap_write_lock_killable(mm))
+		return -EINTR;
+
+	/*
+	 * First pass, this helps to avoid
+	 * partial sealing in case of error in input address range,
+	 * e.g. ENOMEM error.
+	 */
+	ret = check_mm_seal(start, end);
+	if (ret)
+		goto out;
+
+	/*
+	 * Second pass, this should success, unless there are errors
+	 * from vma_modify_flags, e.g. merge/split error, or process
+	 * reaching the max supported VMAs, however, those cases shall
+	 * be rare.
+	 */
+	ret = apply_mm_seal(start, end);
+
+out:
+	mmap_write_unlock(current->mm);
+	return ret;
+}
+
+SYSCALL_DEFINE3(mseal, unsigned long, start, size_t, len, unsigned long,
+		flags)
+{
+	return do_mseal(start, len, flags);
+}