[PATCH] arm64: Allow vmalloc regions to be set with set_memory_*

On 13 January 2016 at 15:03, Ard Biesheuvel [off-list ref] wrote:

quoted

On 12 January 2016 at 22:46, Laura Abbott [off-list ref] wrote:

quoted

The range of set_memory_* is currently restricted to the module address
range because of difficulties in breaking down larger block sizes.
vmalloc maps PAGE_SIZE pages so it is safe to use as well. Update the
function ranges and add a comment explaining why the range is restricted
the way it is.

Signed-off-by: Laura Abbott <redacted>
---
This should let the protections for the eBPF work as expected, I don't
know if there is some sort of self test for thatL.

This is going to conflict with my KASLR implementation, since it puts
the kernel image right in the middle of the vmalloc area, and the
kernel is obviously mapped with block mappings. In fact, I am
proposing enabling huge-vmap for arm64 as well, since it seems an
improvement generally, but also specifically allows me to unmap the
__init section using the generic vunmap code (remove_vm_area). But in
general, I think the assumption that the whole vmalloc area is mapped
using pages is not tenable.

AFAICT, vmalloc still use pages exclusively even with huge-vmap (but
ioremap does not). So perhaps it would make sense to check for the
VM_ALLOC bit in the VMA flags (which I will not set for the kernel
regions either)

Something along these lines, perhaps?

diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c
index 3571c7309c5e..bda0a776c58e 100644
--- a/arch/arm64/mm/pageattr.c
+++ b/arch/arm64/mm/pageattr.c

@@ -13,6 +13,7 @@
  #include <linux/kernel.h>
  #include <linux/mm.h>
  #include <linux/module.h>
+#include <linux/vmalloc.h>
  #include <linux/sched.h>

  #include <asm/pgtable.h>

@@ -44,6 +45,7 @@ static int change_memory_common(unsigned long addr
         unsigned long end = start + size;
         int ret;
         struct page_change_data data;
+       struct vm_struct *area;

         if (!PAGE_ALIGNED(addr)) {
                 start &= PAGE_MASK;

@@ -51,10 +53,14 @@ static int change_memory_common(unsigned long addr,
                 WARN_ON_ONCE(1);
         }

-       if (start < MODULES_VADDR || start >= MODULES_END)
-               return -EINVAL;
-
-       if (end < MODULES_VADDR || end >= MODULES_END)
+       /*
+        * Check whether the [addr, addr + size) interval is entirely
+        * covered by precisely one VM area that has the VM_ALLOC flag set
+        */
+       area = find_vm_area((void *)addr);
+       if (!area ||
+           end > (unsigned long)area->addr + area->size ||
+           !(area->flags & VM_ALLOC))
                 return -EINVAL;

         data.set_mask = set_mask;