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, 3 insertions, 36 deletions

diff --git a/arch/arm64/kernel/vdso.c b/arch/arm64/kernel/vdso.c
index debb8995d57f..cee5d04ea9ad 100644
--- a/arch/arm64/kernel/vdso.c
+++ b/arch/arm64/kernel/vdso.c
@@ -78,17 +78,9 @@ static union {
 } vdso_data_store __page_aligned_data;
 struct vdso_data *vdso_data = vdso_data_store.data;
 
-static int __vdso_remap(enum vdso_abi abi,
-			const struct vm_special_mapping *sm,
-			struct vm_area_struct *new_vma)
+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;
-	unsigned long vdso_size = vdso_info[abi].vdso_code_end -
-				  vdso_info[abi].vdso_code_start;
-
-	if (vdso_size != new_size)
-		return -EINVAL;
-
 	current->mm->context.vdso = (void *)new_vma->vm_start;
 
 	return 0;
@@ -219,17 +211,6 @@ static vm_fault_t vvar_fault(const struct vm_special_mapping *sm,
 	return vmf_insert_pfn(vma, vmf->address, pfn);
 }
 
-static int vvar_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;
-
-	if (new_size != VVAR_NR_PAGES * PAGE_SIZE)
-		return -EINVAL;
-
-	return 0;
-}
-
 static int __setup_additional_pages(enum vdso_abi abi,
 				    struct mm_struct *mm,
 				    struct linux_binprm *bprm,
@@ -280,12 +261,6 @@ up_fail:
 /*
  * Create and map the vectors page for AArch32 tasks.
  */
-static int aarch32_vdso_mremap(const struct vm_special_mapping *sm,
-		struct vm_area_struct *new_vma)
-{
-	return __vdso_remap(VDSO_ABI_AA32, sm, new_vma);
-}
-
 enum aarch32_map {
 	AA32_MAP_VECTORS, /* kuser helpers */
 	AA32_MAP_SIGPAGE,
@@ -308,11 +283,10 @@ static struct vm_special_mapping aarch32_vdso_maps[] = {
 	[AA32_MAP_VVAR] = {
 		.name = "[vvar]",
 		.fault = vvar_fault,
-		.mremap = vvar_mremap,
 	},
 	[AA32_MAP_VDSO] = {
 		.name = "[vdso]",
-		.mremap = aarch32_vdso_mremap,
+		.mremap = vdso_mremap,
 	},
 };
 
@@ -453,12 +427,6 @@ out:
 }
 #endif /* CONFIG_COMPAT */
 
-static int vdso_mremap(const struct vm_special_mapping *sm,
-		struct vm_area_struct *new_vma)
-{
-	return __vdso_remap(VDSO_ABI_AA64, sm, new_vma);
-}
-
 enum aarch64_map {
 	AA64_MAP_VVAR,
 	AA64_MAP_VDSO,
@@ -468,7 +436,6 @@ static struct vm_special_mapping aarch64_vdso_maps[] __ro_after_init = {
 	[AA64_MAP_VVAR] = {
 		.name	= "[vvar]",
 		.fault = vvar_fault,
-		.mremap = vvar_mremap,
 	},
 	[AA64_MAP_VDSO] = {
 		.name	= "[vdso]",