[PATCH] x86: tighten kernel image page access rights

On x86-64, kernel memory freed after init can be entirely unmapped instead
of just getting 'poisoned' by overwriting with a debug pattern.

On i386 and x86-64 (under CONFIG_DEBUG_RODATA), kernel text and bug table
can also be write-protected.

Compared to the first version, this one prevents re-creating deleted
mappings in the kernel image range on x86-64, if those got removed
previously. This, together with the original changes, prevents temporarily
having inconsistent mappings when cacheability attributes are being
changed on such pages (e.g. from AGP code). While on i386 such duplicate
mappings don't exist, the same change is done there, too, both for
consistency and because checking pte_present() before using various other
pte_XXX functions is a requirement anyway. At once, i386 code gets
adjusted to use pte_huge() instead of open coding this.

AK: split out cpa() changes

Signed-off-by: Jan Beulich <jbeulich@novell.com>
Signed-off-by: Andi Kleen <ak@suse.de>

1 files changed, 19 insertions, 6 deletions

diff --git a/arch/i386/mm/init.c b/arch/i386/mm/init.c
index 23be1b0aafa4..bd5ef3718504 100644
--- a/arch/i386/mm/init.c
+++ b/arch/i386/mm/init.c
@@ -22,6 +22,7 @@
 #include <linux/init.h>
 #include <linux/highmem.h>
 #include <linux/pagemap.h>
+#include <linux/pfn.h>
 #include <linux/poison.h>
 #include <linux/bootmem.h>
 #include <linux/slab.h>
@@ -751,13 +752,25 @@ static int noinline do_test_wp_bit(void)
 
 void mark_rodata_ro(void)
 {
-        unsigned long addr = (unsigned long)__start_rodata;
+        unsigned long start = PFN_ALIGN(_text);
+        unsigned long size = PFN_ALIGN(_etext) - start;
 
-        for (; addr < (unsigned long)__end_rodata; addr += PAGE_SIZE)
-                change_page_attr(virt_to_page(addr), 1, PAGE_KERNEL_RO);
+#ifdef CONFIG_HOTPLUG_CPU
+        /* It must still be possible to apply SMP alternatives. */
+        if (num_possible_cpus() <= 1)
+#endif
+        {
+                change_page_attr(virt_to_page(start),
+                                 size >> PAGE_SHIFT, PAGE_KERNEL_RX);
+                printk("Write protecting the kernel text: %luk\n", size >> 10);
+        }
 
-        printk("Write protecting the kernel read-only data: %uk\n",
-                        (__end_rodata - __start_rodata) >> 10);
+        start += size;
+        size = (unsigned long)__end_rodata - start;
+        change_page_attr(virt_to_page(start),
+                         size >> PAGE_SHIFT, PAGE_KERNEL_RO);
+        printk("Write protecting the kernel read-only data: %luk\n",
+               size >> 10);
 
         /*
          * change_page_attr() requires a global_flush_tlb() call after it.
@@ -781,7 +794,7 @@ void free_init_pages(char *what, unsigned long begin, unsigned long end)
                 __free_page(page);
                 totalram_pages++;
         }
-        printk(KERN_INFO "Freeing %s: %ldk freed\n", what, (end - begin) >> 10);
+        printk(KERN_INFO "Freeing %s: %luk freed\n", what, (end - begin) >> 10);
 }
 
 void free_initmem(void)