[PATCH 1/5] x86/pti: check the return value of pti_user_pagetable_walk_p4d

[Jiang Biao]

pti_user_pagetable_walk_p4d() may return NULL, we should check the
return value to avoid NULL pointer dereference.

Signed-off-by: Jiang Biao <jiang.bi...@zte.com.cn>
---
 arch/x86/mm/pti.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/x86/mm/pti.c b/arch/x86/mm/pti.c
index 4d418e7..be9e5bc 100644
--- a/arch/x86/mm/pti.c
+++ b/arch/x86/mm/pti.c
@@ -195,8 +195,10 @@ static p4d_t *pti_user_pagetable_walk_p4d(unsigned long 
address)
 static pmd_t *pti_user_pagetable_walk_pmd(unsigned long address)
 {
        gfp_t gfp = (GFP_KERNEL | __GFP_NOTRACK | __GFP_ZERO);
-       p4d_t *p4d = pti_user_pagetable_walk_p4d(address);
        pud_t *pud;
+       p4d_t *p4d = pti_user_pagetable_walk_p4d(address);
+       if (WARN_ON(!p4d))
+               return NULL;
 
        BUILD_BUG_ON(p4d_large(*p4d) != 0);
        if (p4d_none(*p4d)) {
@@ -354,6 +356,9 @@ static void __init pti_clone_p4d(unsigned long addr)
        pgd_t *kernel_pgd;
 
        user_p4d = pti_user_pagetable_walk_p4d(addr);
+       if (WARN_ON(!user_p4d))
+               return;
+       
        kernel_pgd = pgd_offset_k(addr);
        kernel_p4d = p4d_offset(kernel_pgd, addr);
        *user_p4d = *kernel_p4d;
-- 
2.7.4