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Commit b2b7d986 authored by Jiang Biao's avatar Jiang Biao Committed by Thomas Gleixner
Browse files

x86/pti: Check the return value of pti_user_pagetable_walk_p4d() 



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: default avatarJiang Biao <jiang.biao2@zte.com.cn>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Cc: dave.hansen@linux.intel.com
Cc: luto@kernel.org
Cc: hpa@zytor.com
Cc: albcamus@gmail.com
Cc: zhong.weidong@zte.com.cn
Link: https://lkml.kernel.org/r/1532045192-49622-1-git-send-email-jiang.biao2@zte.com.cn
parent 97193702

arch/x86/mm/pti.c

+9 −2
Original line number Original line Diff line number Diff line
@@ -176,7 +176,7 @@ static p4d_t *pti_user_pagetable_walk_p4d(unsigned long address) 




	if (pgd_none(*pgd)) {

	if (pgd_none(*pgd)) {

		unsigned long new_p4d_page = __get_free_page(gfp);

		unsigned long new_p4d_page = __get_free_page(gfp);

		if (!new_p4d_page)

		if (WARN_ON_ONCE(!new_p4d_page))

			return NULL;

			return NULL;





		set_pgd(pgd, __pgd(_KERNPG_TABLE | __pa(new_p4d_page)));

		set_pgd(pgd, __pgd(_KERNPG_TABLE | __pa(new_p4d_page)));
@@ -195,9 +195,13 @@ static p4d_t *pti_user_pagetable_walk_p4d(unsigned long address) 
static pmd_t *pti_user_pagetable_walk_pmd(unsigned long address)

static pmd_t *pti_user_pagetable_walk_pmd(unsigned long address)

{

{

	gfp_t gfp = (GFP_KERNEL | __GFP_NOTRACK | __GFP_ZERO);

	gfp_t gfp = (GFP_KERNEL | __GFP_NOTRACK | __GFP_ZERO);

	p4d_t *p4d = pti_user_pagetable_walk_p4d(address);

	p4d_t *p4d;

	pud_t *pud;

	pud_t *pud;





	p4d = pti_user_pagetable_walk_p4d(address);

	if (!p4d)

		return NULL;



	BUILD_BUG_ON(p4d_large(*p4d) != 0);

	BUILD_BUG_ON(p4d_large(*p4d) != 0);

	if (p4d_none(*p4d)) {

	if (p4d_none(*p4d)) {

		unsigned long new_pud_page = __get_free_page(gfp);

		unsigned long new_pud_page = __get_free_page(gfp);
@@ -359,6 +363,9 @@ static void __init pti_clone_p4d(unsigned long addr) 
	pgd_t *kernel_pgd;

	pgd_t *kernel_pgd;





	user_p4d = pti_user_pagetable_walk_p4d(addr);

	user_p4d = pti_user_pagetable_walk_p4d(addr);

	if (!user_p4d)

		return;



	kernel_pgd = pgd_offset_k(addr);

	kernel_pgd = pgd_offset_k(addr);

	kernel_p4d = p4d_offset(kernel_pgd, addr);

	kernel_p4d = p4d_offset(kernel_pgd, addr);

	*user_p4d = *kernel_p4d;

	*user_p4d = *kernel_p4d;