Commit 200e46ac authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Liu Shixin
Browse files

x86/mm: Fix pti_clone_pgtable() alignment assumption 

stable inclusion
from stable-v5.10.224
commit d00c9b4bbc442d99e1dafbdfdab848bc1ead73f6
category: bugfix
bugzilla: https://gitee.com/src-openeuler/kernel/issues/IAOXYY
CVE: CVE-2024-44965

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d00c9b4bbc442d99e1dafbdfdab848bc1ead73f6



--------------------------------

[ Upstream commit 41e71dbb0e0a0fe214545fe64af031303a08524c ]

Guenter reported dodgy crashes on an i386-nosmp build using GCC-11
that had the form of endless traps until entry stack exhaust and then

It turned out that pti_clone_pgtable() had alignment assumptions on
the start address, notably it hard assumes start is PMD aligned. This
is true on x86_64, but very much not true on i386.

These assumptions can cause the end condition to malfunction, leading
to a 'short' clone. Guess what happens when the user mapping has a
short copy of the entry text?

Use the correct increment form for addr to avoid alignment
assumptions.

Fixes: 16a3fe63 ("x86/mm/pti: Clone kernel-image on PTE level for 32 bit")
Reported-by: default avatarGuenter Roeck <linux@roeck-us.net>
Tested-by: default avatarGuenter Roeck <linux@roeck-us.net>
Suggested-by: default avatarThomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20240731163105.GG33588@noisy.programming.kicks-ass.net


Signed-off-by: default avatarSasha Levin <sashal@kernel.org>
Signed-off-by: default avatarLiu Shixin <liushixin2@huawei.com>
parent 6f4a2726

arch/x86/mm/pti.c

+3 −3
Original line number Diff line number Diff line
@@ -374,14 +374,14 @@ pti_clone_pgtable(unsigned long start, unsigned long end, 
			 */

			*target_pmd = *pmd;



			addr += PMD_SIZE;

			addr = round_up(addr + 1, PMD_SIZE);



		} else if (level == PTI_CLONE_PTE) {



			/* Walk the page-table down to the pte level */

			pte = pte_offset_kernel(pmd, addr);

			if (pte_none(*pte)) {

				addr += PAGE_SIZE;

				addr = round_up(addr + 1, PAGE_SIZE);

				continue;

			}
@@ -401,7 +401,7 @@ pti_clone_pgtable(unsigned long start, unsigned long end, 
			/* Clone the PTE */

			*target_pte = *pte;



			addr += PAGE_SIZE;

			addr = round_up(addr + 1, PAGE_SIZE);



		} else {

			BUG();