mm: simplify compat_sys_move_pages

The compat move_pages() implementation uses compat_alloc_user_space() for
converting the pointer array.  Moving the compat handling into the
function itself is a bit simpler and lets us avoid the
compat_alloc_user_space() call.

Link: https://lkml.kernel.org/r/20210727144859.4150043-4-arnd@kernel.org
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Eric Biederman <ebiederm@xmission.com>
Cc: Feng Tang <feng.tang@intel.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Helge Deller <deller@gmx.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "James E.J. Bottomley" <James.Bottomley@HansenPartnership.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/migrate.c b/mm/migrate.c
index 24c2ff8..2bc4948 100644 (file)
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1900,6 +1900,23 @@ set_status:
        mmap_read_unlock(mm);
 }
 
+static int get_compat_pages_array(const void __user *chunk_pages[],
+                                 const void __user * __user *pages,
+                                 unsigned long chunk_nr)
+{
+       compat_uptr_t __user *pages32 = (compat_uptr_t __user *)pages;
+       compat_uptr_t p;
+       int i;
+
+       for (i = 0; i < chunk_nr; i++) {
+               if (get_user(p, pages32 + i))
+                       return -EFAULT;
+               chunk_pages[i] = compat_ptr(p);
+       }
+
+       return 0;
+}
+
 /*
  * Determine the nodes of a user array of pages and store it in
  * a user array of status.
@@ -1919,8 +1936,15 @@ static int do_pages_stat(struct mm_struct *mm, unsigned long nr_pages,
                if (chunk_nr > DO_PAGES_STAT_CHUNK_NR)
                        chunk_nr = DO_PAGES_STAT_CHUNK_NR;
 
-               if (copy_from_user(chunk_pages, pages, chunk_nr * sizeof(*chunk_pages)))
-                       break;
+               if (in_compat_syscall()) {
+                       if (get_compat_pages_array(chunk_pages, pages,
+                                                  chunk_nr))
+                               break;
+               } else {
+                       if (copy_from_user(chunk_pages, pages,
+                                     chunk_nr * sizeof(*chunk_pages)))
+                               break;
+               }
 
                do_pages_stat_array(mm, chunk_nr, chunk_pages, chunk_status);
 
@@ -2025,23 +2049,14 @@ SYSCALL_DEFINE6(move_pages, pid_t, pid, unsigned long, nr_pages,
 
 #ifdef CONFIG_COMPAT
 COMPAT_SYSCALL_DEFINE6(move_pages, pid_t, pid, compat_ulong_t, nr_pages,
-                      compat_uptr_t __user *, pages32,
+                      compat_uptr_t __user *, pages,
                       const int __user *, nodes,
                       int __user *, status,
                       int, flags)
 {
-       const void __user * __user *pages;
-       int i;
-
-       pages = compat_alloc_user_space(nr_pages * sizeof(void *));
-       for (i = 0; i < nr_pages; i++) {
-               compat_uptr_t p;
-
-               if (get_user(p, pages32 + i) ||
-                       put_user(compat_ptr(p), pages + i))
-                       return -EFAULT;
-       }
-       return kernel_move_pages(pid, nr_pages, pages, nodes, status, flags);
+       return kernel_move_pages(pid, nr_pages,
+                                (const void __user *__user *)pages,
+                                nodes, status, flags);
 }
 #endif /* CONFIG_COMPAT */