mm: forbid splitting special mappings

Don't allow splitting of vm_special_mapping's.  It affects vdso/vvar
areas.  Uprobes have only one page in xol_area so they aren't affected.

Those restrictions were enforced by checks in .mremap() callbacks.
Restrict resizing with generic .split() callback.

Link: https://lkml.kernel.org/r/20201013013416.390574-7-dima@arista.com
Signed-off-by: Dmitry Safonov <dima@arista.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Brian Geffon <bgeffon@google.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Dave Jiang <dave.jiang@intel.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vishal Verma <vishal.l.verma@intel.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 0 insertions, 17 deletions

diff --git a/arch/x86/entry/vdso/vma.c b/arch/x86/entry/vdso/vma.c
index 9185cb1d13b9..0c942b31825d 100644
--- a/arch/x86/entry/vdso/vma.c
+++ b/arch/x86/entry/vdso/vma.c
@@ -89,30 +89,14 @@ static void vdso_fix_landing(const struct vdso_image *image,
 static int vdso_mremap(const struct vm_special_mapping *sm,
 		struct vm_area_struct *new_vma)
 {
-	unsigned long new_size = new_vma->vm_end - new_vma->vm_start;
 	const struct vdso_image *image = current->mm->context.vdso_image;
 
-	if (image->size != new_size)
-		return -EINVAL;
-
 	vdso_fix_landing(image, new_vma);
 	current->mm->context.vdso = (void __user *)new_vma->vm_start;
 
 	return 0;
 }
 
-static int vvar_mremap(const struct vm_special_mapping *sm,
-		struct vm_area_struct *new_vma)
-{
-	const struct vdso_image *image = new_vma->vm_mm->context.vdso_image;
-	unsigned long new_size = new_vma->vm_end - new_vma->vm_start;
-
-	if (new_size != -image->sym_vvar_start)
-		return -EINVAL;
-
-	return 0;
-}
-
 #ifdef CONFIG_TIME_NS
 static struct page *find_timens_vvar_page(struct vm_area_struct *vma)
 {
@@ -252,7 +236,6 @@ static const struct vm_special_mapping vdso_mapping = {
 static const struct vm_special_mapping vvar_mapping = {
 	.name = "[vvar]",
 	.fault = vvar_fault,
-	.mremap = vvar_mremap,
 };
 
 /*