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Date: Fri, 14 Jun 2019 17:31:49 +0300 From: Andrey Ryabinin <aryabinin@...tuozzo.com> To: Ingo Molnar <mingo@...hat.com>, Thomas Gleixner <tglx@...utronix.de>, Borislav Petkov <bp@...en8.de>, "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org Cc: Alexander Potapenko <glider@...gle.com>, Dmitry Vyukov <dvyukov@...gle.com>, "Kirill A . Shutemov" <kirill@...temov.name>, kasan-dev@...glegroups.com, linux-kernel@...r.kernel.org, Andrey Ryabinin <aryabinin@...tuozzo.com>, stable@...r.kernel.org Subject: [PATCH] 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 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 <kirill@...temov.name> Signed-off-by: Andrey Ryabinin <aryabinin@...tuozzo.com> Cc: <stable@...r.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
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