[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, 111 insertions, 49 deletions

diff --git a/arch/ia64/kernel/efi.c b/arch/ia64/kernel/efi.c
index a3aa45cbcfa0..c485a3b32ba8 100644
--- a/arch/ia64/kernel/efi.c
+++ b/arch/ia64/kernel/efi.c
@@ -247,6 +247,32 @@ typedef struct kern_memdesc {
 
 static kern_memdesc_t *kern_memmap;
 
+#define efi_md_size(md) (md->num_pages << EFI_PAGE_SHIFT)
+
+static inline u64
+kmd_end(kern_memdesc_t *kmd)
+{
+        return (kmd->start + (kmd->num_pages << EFI_PAGE_SHIFT));
+}
+
+static inline u64
+efi_md_end(efi_memory_desc_t *md)
+{
+        return (md->phys_addr + efi_md_size(md));
+}
+
+static inline int
+efi_wb(efi_memory_desc_t *md)
+{
+        return (md->attribute & EFI_MEMORY_WB);
+}
+
+static inline int
+efi_uc(efi_memory_desc_t *md)
+{
+        return (md->attribute & EFI_MEMORY_UC);
+}
+
 static void
 walk (efi_freemem_callback_t callback, void *arg, u64 attr)
 {
@@ -595,8 +621,8 @@ efi_get_iobase (void)
         return 0;
 }
 
-u32
-efi_mem_type (unsigned long phys_addr)
+static efi_memory_desc_t *
+efi_memory_descriptor (unsigned long phys_addr)
 {
         void *efi_map_start, *efi_map_end, *p;
         efi_memory_desc_t *md;
@@ -610,13 +636,13 @@ efi_mem_type (unsigned long phys_addr)
                 md = p;
 
                 if (phys_addr - md->phys_addr < (md->num_pages << EFI_PAGE_SHIFT))
-                         return md->type;
+                         return md;
         }
         return 0;
 }
 
-u64
-efi_mem_attributes (unsigned long phys_addr)
+static int
+efi_memmap_has_mmio (void)
 {
         void *efi_map_start, *efi_map_end, *p;
         efi_memory_desc_t *md;
@@ -629,36 +655,98 @@ efi_mem_attributes (unsigned long phys_addr)
         for (p = efi_map_start; p < efi_map_end; p += efi_desc_size) {
                 md = p;
 
-                if (phys_addr - md->phys_addr < (md->num_pages << EFI_PAGE_SHIFT))
-                        return md->attribute;
+                if (md->type == EFI_MEMORY_MAPPED_IO)
+                        return 1;
         }
         return 0;
 }
+
+u32
+efi_mem_type (unsigned long phys_addr)
+{
+        efi_memory_desc_t *md = efi_memory_descriptor(phys_addr);
+
+        if (md)
+                return md->type;
+        return 0;
+}
+
+u64
+efi_mem_attributes (unsigned long phys_addr)
+{
+        efi_memory_desc_t *md = efi_memory_descriptor(phys_addr);
+
+        if (md)
+                return md->attribute;
+        return 0;
+}
 EXPORT_SYMBOL(efi_mem_attributes);
 
+/*
+ * Determines whether the memory at phys_addr supports the desired
+ * attribute (WB, UC, etc).  If this returns 1, the caller can safely
+ * access *size bytes at phys_addr with the specified attribute.
+ */
+static int
+efi_mem_attribute_range (unsigned long phys_addr, unsigned long *size, u64 attr)
+{
+        efi_memory_desc_t *md = efi_memory_descriptor(phys_addr);
+        unsigned long md_end;
+
+        if (!md || (md->attribute & attr) != attr)
+                return 0;
+
+        do {
+                md_end = efi_md_end(md);
+                if (phys_addr + *size <= md_end)
+                        return 1;
+
+                md = efi_memory_descriptor(md_end);
+                if (!md || (md->attribute & attr) != attr) {
+                        *size = md_end - phys_addr;
+                        return 1;
+                }
+        } while (md);
+        return 0;
+}
+
+/*
+ * For /dev/mem, we only allow read & write system calls to access
+ * write-back memory, because read & write don't allow the user to
+ * control access size.
+ */
 int
 valid_phys_addr_range (unsigned long phys_addr, unsigned long *size)
 {
-        void *efi_map_start, *efi_map_end, *p;
-        efi_memory_desc_t *md;
-        u64 efi_desc_size;
+        return efi_mem_attribute_range(phys_addr, size, EFI_MEMORY_WB);
+}
 
-        efi_map_start = __va(ia64_boot_param->efi_memmap);
-        efi_map_end   = efi_map_start + ia64_boot_param->efi_memmap_size;
-        efi_desc_size = ia64_boot_param->efi_memdesc_size;
+/*
+ * We allow mmap of anything in the EFI memory map that supports
+ * either write-back or uncacheable access.  For uncacheable regions,
+ * the supported access sizes are system-dependent, and the user is
+ * responsible for using the correct size.
+ *
+ * Note that this doesn't currently allow access to hot-added memory,
+ * because that doesn't appear in the boot-time EFI memory map.
+ */
+int
+valid_mmap_phys_addr_range (unsigned long phys_addr, unsigned long *size)
+{
+        if (efi_mem_attribute_range(phys_addr, size, EFI_MEMORY_WB))
+                return 1;
 
-        for (p = efi_map_start; p < efi_map_end; p += efi_desc_size) {
-                md = p;
+        if (efi_mem_attribute_range(phys_addr, size, EFI_MEMORY_UC))
+                return 1;
 
-                if (phys_addr - md->phys_addr < (md->num_pages << EFI_PAGE_SHIFT)) {
-                        if (!(md->attribute & EFI_MEMORY_WB))
-                                return 0;
+        /*
+         * Some firmware doesn't report MMIO regions in the EFI memory map.
+         * The Intel BigSur (a.k.a. HP i2000) has this problem.  In this
+         * case, we can't use the EFI memory map to validate mmap requests.
+         */
+        if (!efi_memmap_has_mmio())
+                return 1;
 
-                        if (*size > md->phys_addr + (md->num_pages << EFI_PAGE_SHIFT) - phys_addr)
-                                *size = md->phys_addr + (md->num_pages << EFI_PAGE_SHIFT) - phys_addr;
-                        return 1;
-                }
-        }
         return 0;
 }
 
@@ -707,32 +795,6 @@ efi_uart_console_only(void)
         return 0;
 }
 
-#define efi_md_size(md) (md->num_pages << EFI_PAGE_SHIFT)
-
-static inline u64
-kmd_end(kern_memdesc_t *kmd)
-{
-        return (kmd->start + (kmd->num_pages << EFI_PAGE_SHIFT));
-}
-
-static inline u64
-efi_md_end(efi_memory_desc_t *md)
-{
-        return (md->phys_addr + efi_md_size(md));
-}
-
-static inline int
-efi_wb(efi_memory_desc_t *md)
-{
-        return (md->attribute & EFI_MEMORY_WB);
-}
-
-static inline int
-efi_uc(efi_memory_desc_t *md)
-{
-        return (md->attribute & EFI_MEMORY_UC);
-}
-
 /*
  * Look for the first granule aligned memory descriptor memory
  * that is big enough to hold EFI memory map. Make sure this