mm: vmalloc: add flag preventing guard hole allocation

For instrumenting global variables KASan will shadow memory backing memory
for modules.  So on module loading we will need to allocate memory for
shadow and map it at address in shadow that corresponds to the address
allocated in module_alloc().

__vmalloc_node_range() could be used for this purpose, except it puts a
guard hole after allocated area.  Guard hole in shadow memory should be a
problem because at some future point we might need to have a shadow memory
at address occupied by guard hole.  So we could fail to allocate shadow
for module_alloc().

Add a new vm_struct flag 'VM_NO_GUARD' indicating that vm area doesn't
have a guard hole.

Signed-off-by: Andrey Ryabinin <a.ryabinin@samsung.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Konstantin Serebryany <kcc@google.com>
Cc: Dmitry Chernenkov <dmitryc@google.com>
Signed-off-by: Andrey Konovalov <adech.fo@gmail.com>
Cc: Yuri Gribov <tetra2005@gmail.com>
Cc: Konstantin Khlebnikov <koct9i@gmail.com>
Cc: Sasha Levin <sasha.levin@oracle.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h
index b87696fdf06ab14d14ff01f5cfd7b2650f1e6c96..1526fe712ca0368e73e0c0659b65baec7a4ddf42 100644 (file)
--- a/include/linux/vmalloc.h
+++ b/include/linux/vmalloc.h
@@ -16,6 +16,7 @@ struct vm_area_struct;                /* vma defining user mapping in mm_types.h */
 #define VM_USERMAP             0x00000008      /* suitable for remap_vmalloc_range */
 #define VM_VPAGES              0x00000010      /* buffer for pages was vmalloc'ed */
 #define VM_UNINITIALIZED       0x00000020      /* vm_struct is not fully initialized */
+#define VM_NO_GUARD            0x00000040      /* don't add guard page */
 /* bits [20..32] reserved for arch specific ioremap internals */
 
 /*
@@ -96,8 +97,12 @@ void vmalloc_sync_all(void);
 
 static inline size_t get_vm_area_size(const struct vm_struct *area)
 {
-       /* return actual size without guard page */
-       return area->size - PAGE_SIZE;
+       if (!(area->flags & VM_NO_GUARD))
+               /* return actual size without guard page */
+               return area->size - PAGE_SIZE;
+       else
+               return area->size;
+
 }
 
 extern struct vm_struct *get_vm_area(unsigned long size, unsigned long flags);

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 39c338896416bd9f70d197ec30ddd003d935c65e..2e74e99d4cfe84e7287e828d2ba4950651e08e37 100644 (file)
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -1324,10 +1324,8 @@ static struct vm_struct *__get_vm_area_node(unsigned long size,
        if (unlikely(!area))
                return NULL;
 
-       /*
-        * We always allocate a guard page.
-        */
-       size += PAGE_SIZE;
+       if (!(flags & VM_NO_GUARD))
+               size += PAGE_SIZE;
 
        va = alloc_vmap_area(size, align, start, end, node, gfp_mask);
        if (IS_ERR(va)) {