x86: cpa, strict range check in try_preserve_large_page()

Right now, we check only the first 4k page for static required protections.
This does not take overlapping regions into account. So we might end up
setting the wrong permissions/protections for other parts of this large page.

This can be optimized further, but correctness is the important part.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 15 insertions, 2 deletions

diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
index e5d29a112d00..440210a2277d 100644
--- a/arch/x86/mm/pageattr.c
+++ b/arch/x86/mm/pageattr.c
@@ -253,10 +253,10 @@ static int
 try_preserve_large_page(pte_t *kpte, unsigned long address,
                         struct cpa_data *cpa)
 {
-        unsigned long nextpage_addr, numpages, pmask, psize, flags;
+        unsigned long nextpage_addr, numpages, pmask, psize, flags, addr;
         pte_t new_pte, old_pte, *tmp;
         pgprot_t old_prot, new_prot;
-        int do_split = 1;
+        int i, do_split = 1;
         unsigned int level;
 
         spin_lock_irqsave(&pgd_lock, flags);
@@ -304,6 +304,19 @@ try_preserve_large_page(pte_t *kpte, unsigned long address,
         new_prot = static_protections(new_prot, address);
 
         /*
+         * We need to check the full range, whether
+         * static_protection() requires a different pgprot for one of
+         * the pages in the range we try to preserve:
+         */
+        addr = address + PAGE_SIZE;
+        for (i = 1; i < cpa->numpages; i++, addr += PAGE_SIZE) {
+                pgprot_t chk_prot = static_protections(new_prot, addr);
+
+                if (pgprot_val(chk_prot) != pgprot_val(new_prot))
+                        goto out_unlock;
+        }
+
+        /*
          * If there are no changes, return. maxpages has been updated
          * above:
          */