From: Jiang Biao <jiang.biao2@xxxxxxxxxx> [ Upstream commit b2b7d986a89b6c94b1331a909de1217214fb08c1 ] pti_user_pagetable_walk_p4d() can return NULL, so the return value should be checked to prevent a NULL pointer dereference. Add the check and a warning when the P4D 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/1532045192-49622-1-git-send-email-jiang.biao2@xxxxxxxxxx Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx> --- arch/x86/mm/pti.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) diff --git a/arch/x86/mm/pti.c b/arch/x86/mm/pti.c index d6f11accd37a..63afd15b32a5 100644 --- a/arch/x86/mm/pti.c +++ b/arch/x86/mm/pti.c @@ -162,7 +162,7 @@ static __init p4d_t *pti_user_pagetable_walk_p4d(unsigned long address) if (pgd_none(*pgd)) { unsigned long new_p4d_page = __get_free_page(gfp); - if (!new_p4d_page) + if (WARN_ON_ONCE(!new_p4d_page)) return NULL; set_pgd(pgd, __pgd(_KERNPG_TABLE | __pa(new_p4d_page))); @@ -181,9 +181,13 @@ static __init p4d_t *pti_user_pagetable_walk_p4d(unsigned long address) static __init 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); + p4d_t *p4d; pud_t *pud; + p4d = pti_user_pagetable_walk_p4d(address); + if (!p4d) + return NULL; + BUILD_BUG_ON(p4d_large(*p4d) != 0); if (p4d_none(*p4d)) { unsigned long new_pud_page = __get_free_page(gfp); @@ -319,6 +323,9 @@ static void __init pti_clone_p4d(unsigned long addr) pgd_t *kernel_pgd; user_p4d = pti_user_pagetable_walk_p4d(addr); + if (!user_p4d) + return; + kernel_pgd = pgd_offset_k(addr); kernel_p4d = p4d_offset(kernel_pgd, addr); *user_p4d = *kernel_p4d; -- 2.17.1
