diff options
authorAndrey Ryabinin <>2019-06-14 17:31:49 +0300
committerThomas Gleixner <>2019-06-14 16:37:30 +0200
commitf3176ec9420de0c385023afa3e4970129444ac2f (patch)
parent8d3289f2fa1e0c7e2f72c7352f1efb75d2ad7c76 (diff)
x86/kasan: Fix boot with 5-level paging and KASAN
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 a physical address. This doesn't make sense because pgd_val() already contains the 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 bits 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 a value with more high bits set and PTE_PFN_MASK wasn't enough to mask out all of them. So it returns a wrong not even canonical address and crashes on the attempt to dereference it. Switch back to pgd_val() & PTE_PFN_MASK to cure the issue. Fixes: 12a8cc7fcf54 ("x86/kasan: Use the same shadow offset for 4- and 5-level paging") Reported-by: Kirill A. Shutemov <> Signed-off-by: Andrey Ryabinin <> Signed-off-by: Thomas Gleixner <> Cc: Borislav Petkov <> Cc: "H. Peter Anvin" <> Cc: Alexander Potapenko <> Cc: Dmitry Vyukov <> Cc: Cc: Cc: <> Link:
1 files changed, 1 insertions, 1 deletions
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);