linux-kernel - Re: KASAN vs. boot-time switching between 4- and 5-level paging

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Date:   Tue, 11 Jul 2017 19:45:48 +0300
From:   Andrey Ryabinin <aryabinin@...tuozzo.com>
To:     Andy Lutomirski <luto@...nel.org>,
        "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     Dmitry Vyukov <dvyukov@...gle.com>,
        Alexander Potapenko <glider@...gle.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "x86@...nel.org" <x86@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, Andi Kleen <ak@...ux.intel.com>,
        Dave Hansen <dave.hansen@...el.com>,
        linux-arch <linux-arch@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        kasan-dev <kasan-dev@...glegroups.com>
Subject: Re: KASAN vs. boot-time switching between 4- and 5-level paging

On 07/11/2017 06:15 PM, Andrey Ryabinin wrote:
> 
> I reproduced this, and this is kasan bug:
> 
>    │0xffffffff84864897 <x86_early_init_platform_quirks+5>   mov    $0xffffffff83f1d0b8,%rdi 
>    │0xffffffff8486489e <x86_early_init_platform_quirks+12>  movabs $0xdffffc0000000000,%rax 
>    │0xffffffff848648a8 <x86_early_init_platform_quirks+22>  push   %rbp
>    │0xffffffff848648a9 <x86_early_init_platform_quirks+23>  mov    %rdi,%rdx  
>    │0xffffffff848648ac <x86_early_init_platform_quirks+26>  shr    $0x3,%rdx
>    │0xffffffff848648b0 <x86_early_init_platform_quirks+30>  mov    %rsp,%rbp
>   >│0xffffffff848648b3 <x86_early_init_platform_quirks+33>  mov    (%rdx,%rax,1),%al
> 
> we crash on the last move which is a read from shadow


Ughh, I forgot about phys_base.
Plus, I added KASAN_SANITIZE_paravirt.o :=n because with PARAVIRTY=y set_pgd() calls native_set_pgd()
from paravirt.c translation unit.



---
 arch/x86/kernel/Makefile    | 1 +
 arch/x86/mm/kasan_init_64.c | 3 ++-
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index 4b994232cb57..5a1f18b87fb2 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -24,6 +24,7 @@ KASAN_SANITIZE_head$(BITS).o				:= n
 KASAN_SANITIZE_dumpstack.o				:= n
 KASAN_SANITIZE_dumpstack_$(BITS).o			:= n
 KASAN_SANITIZE_stacktrace.o := n
+KASAN_SANITIZE_paravirt.o				:= n
 
 OBJECT_FILES_NON_STANDARD_head_$(BITS).o		:= y
 OBJECT_FILES_NON_STANDARD_relocate_kernel_$(BITS).o	:= y
diff --git a/arch/x86/mm/kasan_init_64.c b/arch/x86/mm/kasan_init_64.c
index d79a7ea83d05..d5743fd37df9 100644
--- a/arch/x86/mm/kasan_init_64.c
+++ b/arch/x86/mm/kasan_init_64.c
@@ -72,7 +72,8 @@ static void __init kasan_early_p4d_populate(pgd_t *pgd,
 	 * TODO: we need helpers for this shit
 	 */
 	if (CONFIG_PGTABLE_LEVELS == 5)
-		p4d = ((p4d_t*)((__pa_nodebug(pgd->pgd) & PTE_PFN_MASK) + __START_KERNEL_map))
+		p4d = ((p4d_t*)((__pa_nodebug(pgd->pgd) & PTE_PFN_MASK)
+					+ __START_KERNEL_map - phys_base))
 			+ p4d_index(addr);
 	else
 		p4d = (p4d_t*)pgd;
-- 
2.13.0