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Subject[PATCH RFC 5/5] mm: Add process_vm_mmap()
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This adds a new syscall to map from or to another
process vma. Flag PVMMAP_FIXED may be specified,
its meaning is similar to mmap()'s MAP_FIXED.

@pid > 0 means to map from process of @pid to current,
@pid < 0 means to map from current to @pid process.

VMA are merged on destination, i.e. if source task
has VMA with address [start; end], and we map it sequentially
twice:

process_vm_mmap(@pid, start, start + (end - start)/2, ...);
process_vm_mmap(@pid, start + (end - start)/2, end, ...);

the destination task will have single vma [start, end].

Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
---
include/linux/mm.h | 4 +
include/linux/mm_types.h | 2 +
include/uapi/asm-generic/mman-common.h | 5 +
mm/mmap.c | 108 ++++++++++++++++++++++++++++++++
mm/process_vm_access.c | 71 +++++++++++++++++++++
5 files changed, 190 insertions(+)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 54328d08dbdd..c49bcfac593c 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2382,6 +2382,10 @@ extern int __do_munmap(struct mm_struct *, unsigned long, size_t,
struct list_head *uf, bool downgrade);
extern int do_munmap(struct mm_struct *, unsigned long, size_t,
struct list_head *uf);
+extern unsigned long mmap_process_vm(struct mm_struct *, unsigned long,
+ struct mm_struct *, unsigned long,
+ unsigned long, unsigned long,
+ struct list_head *);

static inline unsigned long
do_mmap_pgoff(struct file *file, unsigned long addr,
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 1815fbc40926..885f256f2fb7 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -261,11 +261,13 @@ struct vm_region {

#ifdef CONFIG_USERFAULTFD
#define NULL_VM_UFFD_CTX ((struct vm_userfaultfd_ctx) { NULL, })
+#define IS_NULL_VM_UFFD_CTX(uctx) ((uctx)->ctx == NULL)
struct vm_userfaultfd_ctx {
struct userfaultfd_ctx *ctx;
};
#else /* CONFIG_USERFAULTFD */
#define NULL_VM_UFFD_CTX ((struct vm_userfaultfd_ctx) {})
+#define IS_NULL_VM_UFFD_CTX(uctx) (true)
struct vm_userfaultfd_ctx {};
#endif /* CONFIG_USERFAULTFD */

diff --git a/include/uapi/asm-generic/mman-common.h b/include/uapi/asm-generic/mman-common.h
index abd238d0f7a4..44cb6cf77e93 100644
--- a/include/uapi/asm-generic/mman-common.h
+++ b/include/uapi/asm-generic/mman-common.h
@@ -28,6 +28,11 @@
/* 0x0100 - 0x80000 flags are defined in asm-generic/mman.h */
#define MAP_FIXED_NOREPLACE 0x100000 /* MAP_FIXED which doesn't unmap underlying mapping */

+/*
+ * Flags for process_vm_mmap
+ */
+#define PVMMAP_FIXED 0x01
+
/*
* Flags for mlock
*/
diff --git a/mm/mmap.c b/mm/mmap.c
index b2a1f77643cd..3dbf280e9f8e 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -3274,6 +3274,114 @@ struct vm_area_struct *copy_vma(struct vm_area_struct **vmap,
return NULL;
}

+static int do_mmap_process_vm(struct vm_area_struct *src_vma,
+ unsigned long src_addr,
+ struct mm_struct *dst_mm,
+ unsigned long dst_addr,
+ unsigned long len,
+ struct list_head *uf)
+{
+ struct vm_area_struct *dst_vma;
+ unsigned long pgoff, ret;
+ bool unused;
+
+ if (do_munmap(dst_mm, dst_addr, len, uf))
+ return -ENOMEM;
+
+ if (src_vma->vm_flags & VM_ACCOUNT) {
+ if (security_vm_enough_memory_mm(dst_mm, len >> PAGE_SHIFT))
+ return -ENOMEM;
+ }
+
+ pgoff = src_vma->vm_pgoff +
+ ((src_addr - src_vma->vm_start) >> PAGE_SHIFT);
+ dst_vma = copy_vma(&src_vma, dst_mm, dst_addr,
+ len, pgoff, &unused, false);
+ if (!dst_vma) {
+ ret = -ENOMEM;
+ goto unacct;
+ }
+
+ ret = copy_page_range(dst_mm, src_vma->vm_mm, src_vma,
+ dst_addr, src_addr, src_addr + len);
+ if (ret) {
+ do_munmap(dst_mm, dst_addr, len, uf);
+ return -ENOMEM;
+ }
+
+ if (dst_vma->vm_file)
+ uprobe_mmap(dst_vma);
+ perf_event_mmap(dst_vma);
+
+ dst_vma->vm_flags |= VM_SOFTDIRTY;
+ vma_set_page_prot(dst_vma);
+
+ vm_stat_account(dst_mm, dst_vma->vm_flags, len >> PAGE_SHIFT);
+ return 0;
+
+unacct:
+ vm_unacct_memory(len >> PAGE_SHIFT);
+ return ret;
+}
+
+unsigned long mmap_process_vm(struct mm_struct *src_mm,
+ unsigned long src_addr,
+ struct mm_struct *dst_mm,
+ unsigned long dst_addr,
+ unsigned long len,
+ unsigned long flags,
+ struct list_head *uf)
+{
+ struct vm_area_struct *src_vma = find_vma(src_mm, src_addr);
+ unsigned long gua_flags = 0;
+ unsigned long ret;
+
+ if (!src_vma || src_vma->vm_start > src_addr)
+ return -EFAULT;
+ if (len > src_vma->vm_end - src_addr)
+ return -EFAULT;
+ if (src_vma->vm_flags & (VM_DONTEXPAND | VM_PFNMAP))
+ return -EFAULT;
+ if (is_vm_hugetlb_page(src_vma) || (src_vma->vm_flags & VM_IO))
+ return -EINVAL;
+ if (dst_mm->map_count + 2 > sysctl_max_map_count)
+ return -ENOMEM;
+ if (!IS_NULL_VM_UFFD_CTX(&src_vma->vm_userfaultfd_ctx))
+ return -ENOTSUPP;
+
+ if (src_vma->vm_flags & VM_SHARED)
+ gua_flags |= MAP_SHARED;
+ else
+ gua_flags |= MAP_PRIVATE;
+ if (vma_is_anonymous(src_vma) || vma_is_shmem(src_vma))
+ gua_flags |= MAP_ANONYMOUS;
+ if (flags & PVMMAP_FIXED)
+ gua_flags |= MAP_FIXED;
+ ret = get_unmapped_area(src_vma->vm_file, dst_addr, len,
+ src_vma->vm_pgoff +
+ ((src_addr - src_vma->vm_start) >> PAGE_SHIFT),
+ gua_flags);
+ if (offset_in_page(ret))
+ return ret;
+ dst_addr = ret;
+
+ /* Check against address space limit. */
+ if (!may_expand_vm(dst_mm, src_vma->vm_flags, len >> PAGE_SHIFT)) {
+ unsigned long nr_pages;
+
+ nr_pages = count_vma_pages_range(dst_mm, dst_addr, dst_addr + len);
+ if (!may_expand_vm(dst_mm, src_vma->vm_flags,
+ (len >> PAGE_SHIFT) - nr_pages))
+ return -ENOMEM;
+ }
+
+ ret = do_mmap_process_vm(src_vma, src_addr, dst_mm, dst_addr, len, uf);
+ if (ret)
+ return ret;
+
+ return dst_addr;
+}
+
/*
* Return true if the calling process may expand its vm space by the passed
* number of pages
diff --git a/mm/process_vm_access.c b/mm/process_vm_access.c
index a447092d4635..7fca2c5c7edd 100644
--- a/mm/process_vm_access.c
+++ b/mm/process_vm_access.c
@@ -17,6 +17,8 @@
#include <linux/ptrace.h>
#include <linux/slab.h>
#include <linux/syscalls.h>
+#include <linux/mman.h>
+#include <linux/userfaultfd_k.h>

#ifdef CONFIG_COMPAT
#include <linux/compat.h>
@@ -295,6 +297,68 @@ static ssize_t process_vm_rw(pid_t pid,
return rc;
}

+static unsigned long process_vm_mmap(pid_t pid, unsigned long src_addr,
+ unsigned long len, unsigned long dst_addr,
+ unsigned long flags)
+{
+ struct mm_struct *src_mm, *dst_mm;
+ struct task_struct *task;
+ unsigned long ret;
+ int depth = 0;
+ LIST_HEAD(uf);
+
+ len = PAGE_ALIGN(len);
+ src_addr = round_down(src_addr, PAGE_SIZE);
+ if (flags & PVMMAP_FIXED)
+ dst_addr = round_down(dst_addr, PAGE_SIZE);
+ else
+ dst_addr = round_hint_to_min(dst_addr);
+
+ if ((flags & ~PVMMAP_FIXED) || len == 0 || len > TASK_SIZE ||
+ src_addr == 0 || dst_addr > TASK_SIZE - len)
+ return -EINVAL;
+ task = find_get_task_by_vpid(pid > 0 ? pid : -pid);
+ if (!task)
+ return -ESRCH;
+ if (unlikely(task->flags & PF_KTHREAD)) {
+ ret = -EINVAL;
+ goto out_put_task;
+ }
+
+ src_mm = mm_access(task, PTRACE_MODE_ATTACH_REALCREDS);
+ if (!src_mm || IS_ERR(src_mm)) {
+ ret = IS_ERR(src_mm) ? PTR_ERR(src_mm) : -ESRCH;
+ goto out_put_task;
+ }
+ dst_mm = current->mm;
+ mmget(dst_mm);
+
+ if (pid < 0)
+ swap(src_mm, dst_mm);
+
+ /* Double lock mm in address order: smallest is the first */
+ if (src_mm < dst_mm) {
+ down_write(&src_mm->mmap_sem);
+ depth = SINGLE_DEPTH_NESTING;
+ }
+ down_write_nested(&dst_mm->mmap_sem, depth);
+ if (src_mm > dst_mm)
+ down_write_nested(&src_mm->mmap_sem, SINGLE_DEPTH_NESTING);
+
+ ret = mmap_process_vm(src_mm, src_addr, dst_mm, dst_addr, len, flags, &uf);
+
+ up_write(&dst_mm->mmap_sem);
+ if (dst_mm != src_mm)
+ up_write(&src_mm->mmap_sem);
+
+ userfaultfd_unmap_complete(dst_mm, &uf);
+ mmput(src_mm);
+ mmput(dst_mm);
+out_put_task:
+ put_task_struct(task);
+ return ret;
+}
+
SYSCALL_DEFINE6(process_vm_readv, pid_t, pid, const struct iovec __user *, lvec,
unsigned long, liovcnt, const struct iovec __user *, rvec,
unsigned long, riovcnt, unsigned long, flags)
@@ -310,6 +374,13 @@ SYSCALL_DEFINE6(process_vm_writev, pid_t, pid,
return process_vm_rw(pid, lvec, liovcnt, rvec, riovcnt, flags, 1);
}

+SYSCALL_DEFINE5(process_vm_mmap, pid_t, pid,
+ unsigned long, src_addr, unsigned long, len,
+ unsigned long, dst_addr, unsigned long, flags)
+{
+ return process_vm_mmap(pid, src_addr, len, dst_addr, flags);
+}
+
#ifdef CONFIG_COMPAT

static ssize_t
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