>
> So, if I understand correctly what's going on in x86_64, your fix
> wouldn't be applicable to i386. In x86_64, every large page has a
> correct "ref_prot" that is the normal setting for that page... but in
> i386, the kernel text area does not--it should ideally be split into
> small pages all the time if there are both kernel code & free pages
> residing in the same 2M area.
>
> Stuart
(This isn't a submission--I'm just posting this for comments.)
Right now, any large page that touches anywhere from PAGE_OFFSET to
__init_end is initially set up as a large, executable page... but some
of this area contains data & free pages. The patch below adds a
"cleanup_nx_in_kerneltext()" function, called at the end of
free_initmem(), which changes these pages--except for the range from
"_text" to "_etext"--to PAGE_KERNEL (i.e., non-executable).
This does result in two large pages being split up into small PTEs
permanently, but all the non-code regions will be non-executable, and
change_page_attr() will work correctly.
What do you think of this? I have tested this on 2.6.12.
(I've attached the patch as a file, too, since my mail server can't be
convinced to not wrap text.)
Stuart
-----
diff -purN --exclude='*.o' --exclude='*.cmd'
linux-2.6.12grep/arch/i386/mm/init.c linux-2.6.12/arch/i386/mm/init.c
--- linux-2.6.12grep/arch/i386/mm/init.c 2005-07-01
15:09:27.000000000 -0500
+++ linux-2.6.12/arch/i386/mm/init.c 2005-07-01 15:13:06.000000000
-0500
@@ -666,6 +666,30 @@ static int noinline do_test_wp_bit(void)
return flag;
}
+extern int change_page_attr_perm(struct page *, int, pgprot_t);
+
+/*
+ * In kernel_physical_mapping_init(), any big pages that contained
kernel text area were
+ * set up as big executable pages. This function should be called when
the initmem
+ * is freed, to correctly set up the executable & non-executable pages
in this area.
+ */
+static void cleanup_nx_in_kerneltext(void)
+{
+ unsigned long from, to;
+
+ if (!nx_enabled) return;
+
+ from = PAGE_OFFSET;
+ to = (unsigned long)_text & PAGE_MASK;
+ for (; from<to; from += PAGE_SIZE)
+ change_page_attr_perm(virt_to_page(from), 1,
PAGE_KERNEL);
+
+ from = ((unsigned long)_etext + PAGE_SIZE - 1) & PAGE_MASK;
+ to = ((unsigned long)__init_end + LARGE_PAGE_SIZE) &
LARGE_PAGE_MASK;
+ for (; from<to; from += PAGE_SIZE)
+ change_page_attr_perm(virt_to_page(from), 1,
PAGE_KERNEL);
+}
+
void free_initmem(void)
{
unsigned long addr;
@@ -679,6 +703,8 @@ void free_initmem(void)
totalram_pages++;
}
printk (KERN_INFO "Freeing unused kernel memory: %dk freed\n",
(__init_end - __init_begin) >> 10);
+
+ cleanup_nx_in_kerneltext();
}
#ifdef CONFIG_BLK_DEV_INITRD
diff -purN --exclude='*.o' --exclude='*.cmd'
linux-2.6.12grep/arch/i386/mm/pageattr.c
linux-2.6.12/arch/i386/mm/pageattr.c
--- linux-2.6.12grep/arch/i386/mm/pageattr.c 2005-07-01
15:09:08.000000000 -0500
+++ linux-2.6.12/arch/i386/mm/pageattr.c 2005-07-01
14:56:06.000000000 -0500
@@ -35,7 +35,7 @@ pte_t *lookup_address(unsigned long addr
return pte_offset_kernel(pmd, address);
}
-static struct page *split_large_page(unsigned long address, pgprot_t
prot)
+static struct page *split_large_page(unsigned long address, pgprot_t
prot, pgprot_t ref_prot)
{
int i;
unsigned long addr;
@@ -53,7 +53,7 @@ static struct page *split_large_page(uns
pbase = (pte_t *)page_address(base);
for (i = 0; i < PTRS_PER_PTE; i++, addr += PAGE_SIZE) {
pbase[i] = pfn_pte(addr >> PAGE_SHIFT,
- addr == address ? prot :
PAGE_KERNEL);
+ addr == address ? prot : ref_prot);
}
return base;
}
@@ -122,7 +122,7 @@ __change_page_attr(struct page *page, pg
if ((pte_val(*kpte) & _PAGE_PSE) == 0) {
set_pte_atomic(kpte, mk_pte(page, prot));
} else {
- struct page *split = split_large_page(address,
prot);
+ struct page *split = split_large_page(address,
prot, PAGE_KERNEL);
if (!split)
return -ENOMEM;
set_pmd_pte(kpte,address,mk_pte(split,
PAGE_KERNEL));
@@ -152,6 +152,38 @@ __change_page_attr(struct page *page, pg
return 0;
}
+static int __change_page_attr_perm (struct page *page, pgprot_t prot)
+{
+ pte_t *kpte;
+ unsigned long address;
+ struct page *kpte_page;
+
+ BUG_ON(PageHighMem(page));
+ address = (unsigned long)page_address(page);
+
+ kpte = lookup_address(address);
+ if (!kpte)
+ return -EINVAL;
+ kpte_page = virt_to_page(kpte);
+
+ if ((pte_val(*kpte) & _PAGE_PSE) == 0) {
+ set_pte_atomic(kpte, mk_pte(page, prot));
+ } else {
+ pgprot_t ref_prot;
+
+ if ((pte_val(*kpte) & _PAGE_NX))
+ ref_prot = PAGE_KERNEL;
+ else
+ ref_prot = PAGE_KERNEL_EXEC;
+ kpte_page = split_large_page(address, prot, ref_prot);
+ if (!kpte_page)
+ return -ENOMEM;
+ set_pmd_pte(kpte,address,mk_pte(kpte_page, ref_prot));
+ }
+ SetPageReserved(kpte_page);
+ return 0;
+}
+
static inline void flush_map(void)
{
on_each_cpu(flush_kernel_map, NULL, 1, 1);
@@ -186,6 +218,22 @@ int change_page_attr(struct page *page,
return err;
}
+int change_page_attr_perm(struct page *page, int numpages, pgprot_t
prot)
+{
+ int err = 0;
+ int i;
+ unsigned long flags;
+
+ spin_lock_irqsave(&cpa_lock, flags);
+ for (i = 0; i < numpages; i++, page++) {
+ err = __change_page_attr_perm(page, prot);
+ if (err)
+ break;
+ }
+ spin_unlock_irqrestore(&cpa_lock, flags);
+ return err;
+}
+
void global_flush_tlb(void)
{
LIST_HEAD(l);
Attachment:
pass1.patch
Description: pass1.patch
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