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Date: Mon, 17 Jun 2019 23:10:21 +0200 From: Greg Kroah-Hartman <gregkh@...uxfoundation.org> To: linux-kernel@...r.kernel.org Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, stable@...r.kernel.org, "Kirill A. Shutemov" <kirill@...temov.name>, Andrey Ryabinin <aryabinin@...tuozzo.com>, Thomas Gleixner <tglx@...utronix.de>, Borislav Petkov <bp@...en8.de>, "H. Peter Anvin" <hpa@...or.com>, Alexander Potapenko <glider@...gle.com>, Dmitry Vyukov <dvyukov@...gle.com>, kasan-dev@...glegroups.com Subject: [PATCH 4.19 70/75] x86/kasan: Fix boot with 5-level paging and KASAN From: Andrey Ryabinin <aryabinin@...tuozzo.com> commit f3176ec9420de0c385023afa3e4970129444ac2f upstream. 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 <kirill@...temov.name> Signed-off-by: Andrey Ryabinin <aryabinin@...tuozzo.com> Signed-off-by: Thomas Gleixner <tglx@...utronix.de> Cc: Borislav Petkov <bp@...en8.de> Cc: "H. Peter Anvin" <hpa@...or.com> Cc: Alexander Potapenko <glider@...gle.com> Cc: Dmitry Vyukov <dvyukov@...gle.com> Cc: kasan-dev@...glegroups.com Cc: stable@...r.kernel.org Cc: <stable@...r.kernel.org> Link: https://lkml.kernel.org/r/20190614143149.2227-1-aryabinin@virtuozzo.com Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org> --- arch/x86/mm/kasan_init_64.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/arch/x86/mm/kasan_init_64.c +++ b/arch/x86/mm/kasan_init_64.c @@ -198,7 +198,7 @@ static inline p4d_t *early_p4d_offset(pg 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); }
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