x86/mm: Fix pti_clone_pgtable() alignment assumption
[ 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
#DF from the stack guard.
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.
BUG=b/371693038
TEST=presubmit
RELEASE_NOTE=Fixed CVE-2024-44965 in the Linux kernel.
cos-patch: security-moderate
Fixes: 16a3fe634f6a ("x86/mm/pti: Clone kernel-image on PTE level for 32 bit")
Reported-by: Guenter Roeck <linux@roeck-us.net>
Tested-by: Guenter Roeck <linux@roeck-us.net>
Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Change-Id: Ibc6ea31b54b5a30df456a557601c025e45362f81
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20240731163105.GG33588@noisy.programming.kicks-ass.net
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Kernel CVE Triage Automation <cloud-image-kernel-cve-triage-automation@prod.google.com>
Reviewed-on: https://cos-review.googlesource.com/c/third_party/kernel/+/82904
Tested-by: Cusky Presubmit Bot <presubmit@cos-infra-prod.iam.gserviceaccount.com>
Reviewed-by: Shuo Yang <gshuoy@google.com>
Reviewed-by: Anil Altinay <aaltinay@google.com>
diff --git a/arch/x86/mm/pti.c b/arch/x86/mm/pti.c
index 51b6b78..f7d1bbe 100644
--- a/arch/x86/mm/pti.c
+++ b/arch/x86/mm/pti.c
@@ -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();
