Commit c519c3c0 authored by Alexander Gordeev's avatar Alexander Gordeev Committed by Andrew Morton
Browse files

mm/kasan: avoid lazy MMU mode hazards 

Functions __kasan_populate_vmalloc() and __kasan_depopulate_vmalloc() use
apply_to_pte_range(), which enters lazy MMU mode.  In that mode updating
PTEs may not be observed until the mode is left.

That may lead to a situation in which otherwise correct reads and writes
to a PTE using ptep_get(), set_pte(), pte_clear() and other access
primitives bring wrong results when the vmalloc shadow memory is being
(de-)populated.

To avoid these hazards leave the lazy MMU mode before and re-enter it
after each PTE manipulation.

Link: https://lkml.kernel.org/r/0d2efb7ddddbff6b288fbffeeb10166e90771718.1755528662.git.agordeev@linux.ibm.com


Fixes: 3c5c3cfb ("kasan: support backing vmalloc space with real shadow memory")
Signed-off-by: default avatarAlexander Gordeev <agordeev@linux.ibm.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Daniel Axtens <dja@axtens.net>
Cc: Marc Rutland <mark.rutland@arm.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 08c7c253

mm/kasan/shadow.c

+8 −0
Original line number Diff line number Diff line
@@ -305,6 +305,8 @@ static int kasan_populate_vmalloc_pte(pte_t *ptep, unsigned long addr, 
	pte_t pte;

	int index;



	arch_leave_lazy_mmu_mode();



	index = PFN_DOWN(addr - data->start);

	page = data->pages[index];

	__memset(page_to_virt(page), KASAN_VMALLOC_INVALID, PAGE_SIZE);
@@ -317,6 +319,8 @@ static int kasan_populate_vmalloc_pte(pte_t *ptep, unsigned long addr, 
	}

	spin_unlock(&init_mm.page_table_lock);



	arch_enter_lazy_mmu_mode();



	return 0;

}
@@ -461,6 +465,8 @@ static int kasan_depopulate_vmalloc_pte(pte_t *ptep, unsigned long addr, 
	pte_t pte;

	int none;



	arch_leave_lazy_mmu_mode();



	spin_lock(&init_mm.page_table_lock);

	pte = ptep_get(ptep);

	none = pte_none(pte);
@@ -471,6 +477,8 @@ static int kasan_depopulate_vmalloc_pte(pte_t *ptep, unsigned long addr, 
	if (likely(!none))

		__free_page(pfn_to_page(pte_pfn(pte)));



	arch_enter_lazy_mmu_mode();



	return 0;

}