From: Jiang Biao <jiang.biao2@xxxxxxxxxx> [ Upstream commit 8c934e01a7ce685d98e970880f5941d79272c654 ] pti_user_pagetable_walk_pmd() can return NULL, so the return value should be checked to prevent a NULL pointer dereference. Add the check and a warning when the PMD allocation fails. Signed-off-by: Jiang Biao <jiang.biao2@xxxxxxxxxx> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: dave.hansen@xxxxxxxxxxxxxxx Cc: luto@xxxxxxxxxx Cc: hpa@xxxxxxxxx Cc: albcamus@xxxxxxxxx Cc: zhong.weidong@xxxxxxxxxx Link: https://lkml.kernel.org/r/1532045192-49622-2-git-send-email-jiang.biao2@xxxxxxxxxx Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx> --- arch/x86/mm/pti.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) diff --git a/arch/x86/mm/pti.c b/arch/x86/mm/pti.c index 51abd8292b6d..ffa2f0f67904 100644 --- a/arch/x86/mm/pti.c +++ b/arch/x86/mm/pti.c @@ -206,7 +206,7 @@ static pmd_t *pti_user_pagetable_walk_pmd(unsigned long address) BUILD_BUG_ON(p4d_large(*p4d) != 0); if (p4d_none(*p4d)) { unsigned long new_pud_page = __get_free_page(gfp); - if (!new_pud_page) + if (WARN_ON_ONCE(!new_pud_page)) return NULL; set_p4d(p4d, __p4d(_KERNPG_TABLE | __pa(new_pud_page))); @@ -220,7 +220,7 @@ static pmd_t *pti_user_pagetable_walk_pmd(unsigned long address) } if (pud_none(*pud)) { unsigned long new_pmd_page = __get_free_page(gfp); - if (!new_pmd_page) + if (WARN_ON_ONCE(!new_pmd_page)) return NULL; set_pud(pud, __pud(_KERNPG_TABLE | __pa(new_pmd_page))); @@ -242,9 +242,13 @@ static pmd_t *pti_user_pagetable_walk_pmd(unsigned long address) static __init pte_t *pti_user_pagetable_walk_pte(unsigned long address) { gfp_t gfp = (GFP_KERNEL | __GFP_NOTRACK | __GFP_ZERO); - pmd_t *pmd = pti_user_pagetable_walk_pmd(address); + pmd_t *pmd; pte_t *pte; + pmd = pti_user_pagetable_walk_pmd(address); + if (!pmd) + return NULL; + /* We can't do anything sensible if we hit a large mapping. */ if (pmd_large(*pmd)) { WARN_ON(1); -- 2.17.1
