mm: abstract moving to the next PFN

In order to fix the L1TF vulnerability, x86 can invert the PTE bits for
PROT_NONE VMAs, which means we cannot move from one PTE to the next by
adding 1 to the PFN field of the PTE.  This results in the BUG reported at
[1].

Abstract advancing the PTE to the next PFN through a pte_next_pfn()
function/macro.

Link: https://lkml.kernel.org/r/20230920040958.866520-1-willy@infradead.org
Fixes: bcc6cc832573 ("mm: add default definition of set_ptes()")
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reported-by: syzbot+55cc72f8cc3a549119df@syzkaller.appspotmail.com
Closes: https://lkml.kernel.org/r/000000000000d099fa0604f03351@google.com [1]
Reviewed-by: Yin Fengwei <fengwei.yin@intel.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
index d6ad98c..e02b179 100644 (file)
--- a/arch/x86/include/asm/pgtable.h
+++ b/arch/x86/include/asm/pgtable.h
@@ -955,6 +955,14 @@ static inline int pte_same(pte_t a, pte_t b)
        return a.pte == b.pte;
 }
 
+static inline pte_t pte_next_pfn(pte_t pte)
+{
+       if (__pte_needs_invert(pte_val(pte)))
+               return __pte(pte_val(pte) - (1UL << PFN_PTE_SHIFT));
+       return __pte(pte_val(pte) + (1UL << PFN_PTE_SHIFT));
+}
+#define pte_next_pfn   pte_next_pfn
+
 static inline int pte_present(pte_t a)
 {
        return pte_flags(a) & (_PAGE_PRESENT | _PAGE_PROTNONE);

diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
index 1fba072..af7639c 100644 (file)
--- a/include/linux/pgtable.h
+++ b/include/linux/pgtable.h
@@ -206,6 +206,14 @@ static inline int pmd_young(pmd_t pmd)
 #endif
 
 #ifndef set_ptes
+
+#ifndef pte_next_pfn
+static inline pte_t pte_next_pfn(pte_t pte)
+{
+       return __pte(pte_val(pte) + (1UL << PFN_PTE_SHIFT));
+}
+#endif
+
 /**
  * set_ptes - Map consecutive pages to a contiguous range of addresses.
  * @mm: Address space to map the pages into.
@@ -231,7 +239,7 @@ static inline void set_ptes(struct mm_struct *mm, unsigned long addr,
                if (--nr == 0)
                        break;
                ptep++;
-               pte = __pte(pte_val(pte) + (1UL << PFN_PTE_SHIFT));
+               pte = pte_next_pfn(pte);
        }
        arch_leave_lazy_mmu_mode();
 }