Since commit d52888aa2753 ("x86/mm: Move LDT remap out of KASLR region on
5-level paging") kernel doesn't boot with KASAN on 5-level paging machines.
The bug is actually in early_p4d_offset() and introduced by commit
12a8cc7fcf54 ("x86/kasan: Use the same shadow offset for 4- and 5-level paging")
early_p4d_offset() tries to convert pgd_val(*pgd) value to physical
address. This doesn't make sense because pgd_val() already contains
physical address.
It did work prior to commit d52888aa2753 because the result of
"__pa_nodebug(pgd_val(*pgd)) & PTE_PFN_MASK" was the same as
"pgd_val(*pgd) & PTE_PFN_MASK". __pa_nodebug() just set some high bit
which were masked out by applying PTE_PFN_MASK.
After the change of the PAGE_OFFSET offset in commit d52888aa2753
__pa_nodebug(pgd_val(*pgd)) started to return value with more high bits
set and PTE_PFN_MASK wasn't enough to mask out all of them. So we've got
wrong not even canonical address and crash on the attempt to dereference it.
Fixes: 12a8cc7fcf54 ("x86/kasan: Use the same shadow offset for 4- and 5-level
paging")
Reported-by: Kirill A. Shutemov <kir...@shutemov.name>
Signed-off-by: Andrey Ryabinin <aryabi...@virtuozzo.com>
Cc: <sta...@vger.kernel.org>
---
arch/x86/mm/kasan_init_64.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/x86/mm/kasan_init_64.c b/arch/x86/mm/kasan_init_64.c
index 8dc0fc0b1382..296da58f3013 100644
--- a/arch/x86/mm/kasan_init_64.c
+++ b/arch/x86/mm/kasan_init_64.c
@@ -199,7 +199,7 @@ static inline p4d_t *early_p4d_offset(pgd_t *pgd, unsigned
long addr)
if (!pgtable_l5_enabled())
return (p4d_t *)pgd;
- p4d = __pa_nodebug(pgd_val(*pgd)) & PTE_PFN_MASK;
+ p4d = pgd_val(*pgd) & PTE_PFN_MASK;
p4d += __START_KERNEL_map - phys_base;
return (p4d_t *)p4d + p4d_index(addr);
}
--
2.21.0
