[RFC,v3,01/11] mseal: Add mseal syscall.

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 19fc73b02c9f..3d1120570de5 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -30,6 +30,7 @@ 
 #include <linux/kasan.h>
 #include <linux/memremap.h>
 #include <linux/slab.h>
+#include <uapi/linux/mman.h>
 
 struct mempolicy;
 struct anon_vma;
@@ -257,9 +258,17 @@  extern struct rw_semaphore nommu_region_sem;
 extern unsigned int kobjsize(const void *objp);
 #endif
 
+/*
+ * MM_SEAL_ALL is all supported flags in mseal().
+ */
+#define MM_SEAL_ALL ( \
+	MM_SEAL_SEAL | \
+	MM_SEAL_BASE | \
+	MM_SEAL_PROT_PKEY)
+
 /*
  * vm_flags in vm_area_struct, see mm_types.h.
- * When changing, update also include/trace/events/mmflags.h
+ * When changing, update also include/trace/events/mmflags.h.
  */
 #define VM_NONE		0x00000000
 
@@ -3308,6 +3317,40 @@  static inline void mm_populate(unsigned long addr, unsigned long len)
 static inline void mm_populate(unsigned long addr, unsigned long len) {}
 #endif
 
+#ifdef CONFIG_MSEAL
+static inline bool check_vma_seals_mergeable(unsigned long vm_seals)
+{
+	/*
+	 * Set sealed VMA not mergeable with another VMA for now.
+	 * This will be changed in later commit to make sealed
+	 * VMA also mergeable.
+	 */
+	if (vm_seals & MM_SEAL_ALL)
+		return false;
+
+	return true;
+}
+
+/*
+ * return the valid sealing (after mask).
+ */
+static inline unsigned long vma_seals(struct vm_area_struct *vma)
+{
+	return (vma->vm_seals & MM_SEAL_ALL);
+}
+
+#else
+static inline bool check_vma_seals_mergeable(unsigned long vm_seals1)
+{
+	return true;
+}
+
+static inline unsigned long vma_seals(struct vm_area_struct *vma)
+{
+	return 0;
+}
+#endif
+
 /* These take the mm semaphore themselves */
 extern int __must_check vm_brk(unsigned long, unsigned long);
 extern int __must_check vm_brk_flags(unsigned long, unsigned long, unsigned long);
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 589f31ef2e84..052799173c86 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -687,6 +687,13 @@  struct vm_area_struct {
 	struct vma_numab_state *numab_state;	/* NUMA Balancing state */
 #endif
 	struct vm_userfaultfd_ctx vm_userfaultfd_ctx;
+#ifdef CONFIG_MSEAL
+	/*
+	 * bit masks for seal.
+	 * need this since vm_flags is full.
+	 */
+	unsigned long vm_seals;		/* seal flags, see mm.h. */
+#endif
 } __randomize_layout;
 
 #ifdef CONFIG_SCHED_MM_CID
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index 0901af60d971..b1c766b74765 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -812,6 +812,8 @@  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 types,
+			  unsigned long flags);
 asmlinkage long sys_mbind(unsigned long start, unsigned long len,
 				unsigned long mode,
 				const unsigned long __user *nmask,
diff --git a/include/uapi/linux/mman.h b/include/uapi/linux/mman.h
index a246e11988d5..f561652886c4 100644
--- a/include/uapi/linux/mman.h
+++ b/include/uapi/linux/mman.h
@@ -55,4 +55,8 @@  struct cachestat {
 	__u64 nr_recently_evicted;
 };
 
+#define MM_SEAL_SEAL		_BITUL(0)
+#define MM_SEAL_BASE		_BITUL(1)
+#define MM_SEAL_PROT_PKEY	_BITUL(2)
+
 #endif /* _UAPI_LINUX_MMAN_H */
diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
index 9db51ea373b0..716d64df522d 100644
--- a/kernel/sys_ni.c
+++ b/kernel/sys_ni.c
@@ -195,6 +195,7 @@  COND_SYSCALL(migrate_pages);
 COND_SYSCALL(move_pages);
 COND_SYSCALL(set_mempolicy_home_node);
 COND_SYSCALL(cachestat);
+COND_SYSCALL(mseal);
 
 COND_SYSCALL(perf_event_open);
 COND_SYSCALL(accept4);
diff --git a/mm/Kconfig b/mm/Kconfig
index 264a2df5ecf5..63972d476d19 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -1258,6 +1258,15 @@  config LOCK_MM_AND_FIND_VMA
 	bool
 	depends on !STACK_GROWSUP
 
+config MSEAL
+	default n
+	bool "Enable mseal() system call"
+	depends on MMU
+	help
+	  Enable the virtual memory sealing.
+	  This feature allows sealing each virtual memory area separately with
+	  multiple sealing types.
+
 source "mm/damon/Kconfig"
 
 endmenu
diff --git a/mm/Makefile b/mm/Makefile
index ec65984e2ade..643d8518dac0 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -120,6 +120,7 @@  obj-$(CONFIG_PAGE_EXTENSION) += page_ext.o
 obj-$(CONFIG_PAGE_TABLE_CHECK) += page_table_check.o
 obj-$(CONFIG_CMA_DEBUGFS) += cma_debug.o
 obj-$(CONFIG_SECRETMEM) += secretmem.o
+obj-$(CONFIG_MSEAL) += mseal.o
 obj-$(CONFIG_CMA_SYSFS) += cma_sysfs.o
 obj-$(CONFIG_USERFAULTFD) += userfaultfd.o
 obj-$(CONFIG_IDLE_PAGE_TRACKING) += page_idle.o
diff --git a/mm/mmap.c b/mm/mmap.c
index 9e018d8dd7d6..42462c2a0c35 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -740,6 +740,9 @@  static inline bool is_mergeable_vma(struct vm_area_struct *vma,
 		return false;
 	if (!anon_vma_name_eq(anon_vma_name(vma), anon_name))
 		return false;
+	if (!check_vma_seals_mergeable(vma_seals(vma)))
+		return false;
+
 	return true;
 }
 
diff --git a/mm/mseal.c b/mm/mseal.c
new file mode 100644
index 000000000000..13bbe9ef5883
--- /dev/null
+++ b/mm/mseal.c
@@ -0,0 +1,257 @@ 
+// SPDX-License-Identifier: GPL-2.0
+/*
+ *  Implement mseal() syscall.
+ *
+ *  Copyright (c) 2023 Google, Inc.
+ *
+ *  Author: Jeff Xu <jeffxu@chromium.org>
+ */
+
+#include <linux/mman.h>
+#include <linux/mm.h>
+#include <linux/syscalls.h>
+#include <linux/sched.h>
+#include "internal.h"
+
+static bool can_do_mseal(unsigned long types, unsigned long flags)
+{
+	/* check types is a valid bitmap. */
+	if (types & ~MM_SEAL_ALL)
+		return false;
+
+	/* flags isn't used for now. */
+	if (flags)
+		return false;
+
+	return true;
+}
+
+/*
+ * Check if a seal type can be added to VMA.
+ */
+static bool can_add_vma_seals(struct vm_area_struct *vma, unsigned long newSeals)
+{
+	/* When SEAL_MSEAL is set, reject if a new type of seal is added. */
+	if ((vma->vm_seals & MM_SEAL_SEAL) &&
+	    (newSeals & ~(vma_seals(vma))))
+		return false;
+
+	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, unsigned long addtypes)
+{
+	int ret = 0;
+
+	if (addtypes & ~(vma_seals(vma))) {
+		/*
+		 * Handle split at start and end.
+		 * For now sealed VMA doesn't merge with other VMAs.
+		 * This will be updated in later commit to make
+		 * sealed VMA also mergeable.
+		 */
+		if (start != vma->vm_start) {
+			ret = split_vma(vmi, vma, start, 1);
+			if (ret)
+				goto out;
+		}
+
+		if (end != vma->vm_end) {
+			ret = split_vma(vmi, vma, end, 0);
+			if (ret)
+				goto out;
+		}
+
+		vma->vm_seals |= addtypes;
+	}
+
+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> requested seal type can be added in given address range.
+ */
+static int check_mm_seal(unsigned long start, unsigned long end,
+			 unsigned long newtypes)
+{
+	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 (!can_add_vma_seals(vma, newtypes))
+			return -EACCES;
+
+		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 newtypes)
+{
+	unsigned long nstart, nend;
+	struct vm_area_struct *vma, *prev = NULL;
+	struct vma_iterator vmi;
+	int error = 0;
+
+	vma_iter_init(&vmi, current->mm, start);
+	vma = vma_find(&vmi, end);
+
+	prev = vma_prev(&vmi);
+	if (start > vma->vm_start)
+		prev = vma;
+
+	nstart = start;
+
+	/* going through each vma to update. */
+	for_each_vma_range(vmi, vma, end) {
+		nend = vma->vm_end;
+		if (nend > end)
+			nend = end;
+
+		error = mseal_fixup(&vmi, vma, &prev, nstart, nend, newtypes);
+		if (error)
+			break;
+
+		nstart = vma->vm_end;
+	}
+
+	return error;
+}
+
+/*
+ * 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.
+ *
+ *  types: bit mask for sealed syscalls.
+ *   MM_SEAL_BASE: prevent VMA from:
+ *   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> Move or expand a different vma into the current location,
+ *	via mremap().
+ *   3> Modifying sealed 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.
+ *
+ *   The MM_SEAL_PROT_PKEY:
+ *	Seal PROT and PKEY of the address range, in other words,
+ *	mprotect() and pkey_mprotect() will be denied if the memory is
+ *	sealed with MM_SEAL_PROT_PKEY.
+ *
+ *   The MM_SEAL_SEAL
+ *	MM_SEAL_SEAL denies adding a new seal for an VMA.
+ *
+ *	The kernel will remember which seal types are applied, and the
+ *	application doesn’t need to repeat all existing seal types in
+ *	the next mseal(). Once a seal type is applied, it can’t be
+ *	unsealed. Call mseal() on an existing seal type is a no-action,
+ *	not a failure.
+ *
+ *  flags: reserved.
+ *
+ * return values:
+ *  zero: success.
+ *  -EINVAL:
+ *   invalid seal type.
+ *   invalid input flags.
+ *   addr is not page aligned.
+ *   addr + len overflow.
+ *  -ENOMEM:
+ *   addr is not a valid address (not allocated).
+ *   end (addr + len) is not a valid address.
+ *   a gap (unallocated memory) between start and end.
+ *  -EACCES:
+ *   MM_SEAL_SEAL is set, adding a new seal is rejected.
+ *
+ * Note:
+ *  user can call mseal(2) multiple times to add new seal types.
+ *  adding an already added seal type is a no-action (no error).
+ *  adding a new seal type after MM_SEAL_SEAL will be rejected.
+ *  unseal() or removing a seal type is not supported.
+ */
+static int do_mseal(unsigned long start, size_t len_in, unsigned long types,
+		    unsigned long flags)
+{
+	int ret = 0;
+	unsigned long end;
+	struct mm_struct *mm = current->mm;
+	size_t len;
+
+	/* MM_SEAL_BASE is set when other seal types are set. */
+	if (types & MM_SEAL_PROT_PKEY)
+		types |= MM_SEAL_BASE;
+
+	if (!can_do_mseal(types, flags))
+		return -EINVAL;
+
+	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;
+
+	ret = check_mm_seal(start, end, types);
+	if (ret)
+		goto out;
+
+	ret = apply_mm_seal(start, end, types);
+
+out:
+	mmap_write_unlock(current->mm);
+	return ret;
+}
+
+SYSCALL_DEFINE4(mseal, unsigned long, start, size_t, len, unsigned long, types, unsigned long,
+		flags)
+{
+	return do_mseal(start, len, types, flags);
+}