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

[Andrey Ryabinin]

On 07/11/2017 06:15 PM, Andrey Ryabinin wrote:
> 
> I reproduced this, and this is kasan bug:
> 
>    â0xffffffff84864897 <x86_early_init_platform_quirks+5>   mov    $0xffffffff83f1d0b8,%rdi 
>    â0xffffffff8486489e <x86_early_init_platform_quirks+12>  movabs $0xdffffc0000000000,%rax 
>    â0xffffffff848648a8 <x86_early_init_platform_quirks+22>  push   %rbp
>    â0xffffffff848648a9 <x86_early_init_platform_quirks+23>  mov    %rdi,%rdx  
>    â0xffffffff848648ac <x86_early_init_platform_quirks+26>  shr    $0x3,%rdx
>    â0xffffffff848648b0 <x86_early_init_platform_quirks+30>  mov    %rsp,%rbp
>   >â0xffffffff848648b3 <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