[PATCH] /dev/mem: validate mmap requests

Add a hook so architectures can validate /dev/mem mmap requests.

This is analogous to validation we already perform in the read/write
paths.

The identity mapping scheme used on ia64 requires that each 16MB or
64MB granule be accessed with exactly one attribute (write-back or
uncacheable).  This avoids "attribute aliasing", which can cause a
machine check.

Sample problem scenario:
  - Machine supports VGA, so it has uncacheable (UC) MMIO at 640K-768K
  - efi_memmap_init() discards any write-back (WB) memory in the first granule
  - Application (e.g., "hwinfo") mmaps /dev/mem, offset 0
  - hwinfo receives UC mapping (the default, since memmap says "no WB here")
  - Machine check abort (on chipsets that don't support UC access to WB
    memory, e.g., sx1000)

In the scenario above, the only choices are
  - Use WB for hwinfo mmap.  Can't do this because it causes attribute
    aliasing with the UC mapping for the VGA MMIO space.
  - Use UC for hwinfo mmap.  Can't do this because the chipset may not
    support UC for that region.
  - Disallow the hwinfo mmap with -EINVAL.  That's what this patch does.

Signed-off-by: Bjorn Helgaas <bjorn.helgaas@hp.com>
Cc: Hugh Dickins <hugh@veritas.com>
Cc: "Luck, Tony" <tony.luck@intel.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 12 insertions, 2 deletions

diff --git a/drivers/char/mem.c b/drivers/char/mem.c
index ce3ff8641191..5b2d18035073 100644
--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -101,6 +101,11 @@ static inline int valid_phys_addr_range(unsigned long addr, size_t *count)
 
         return 1;
 }
+
+static inline int valid_mmap_phys_addr_range(unsigned long addr, size_t *size)
+{
+        return 1;
+}
 #endif
 
 /*
@@ -244,15 +249,20 @@ static pgprot_t phys_mem_access_prot(struct file *file, unsigned long pfn,
 
 static int mmap_mem(struct file * file, struct vm_area_struct * vma)
 {
+        size_t size = vma->vm_end - vma->vm_start;
+
+        if (!valid_mmap_phys_addr_range(vma->vm_pgoff << PAGE_SHIFT, &size))
+                return -EINVAL;
+
         vma->vm_page_prot = phys_mem_access_prot(file, vma->vm_pgoff,
-                                                 vma->vm_end - vma->vm_start,
+                                                 size,
                                                  vma->vm_page_prot);
 
         /* Remap-pfn-range will mark the range VM_IO and VM_RESERVED */
         if (remap_pfn_range(vma,
                             vma->vm_start,
                             vma->vm_pgoff,
-                            vma->vm_end-vma->vm_start,
+                            size,
                             vma->vm_page_prot))
                 return -EAGAIN;
         return 0;