Re: linux/master crashes on boot with KASAN=y

[Jakub Kicinski]

On Sat, 23 Dec 2017 15:41:27 +0300, Andrey Ryabinin wrote:
> On 12/23/2017 11:01 AM, Jakub Kicinski wrote:
> > Hi!
> > 
> > I bisected a crash on boot to this:
> > 
> > commit 21506525fb8ddb0342f2a2370812d47f6a1f3833 (HEAD, refs/bisect/bad)
> > Author: Andy Lutomirski <luto@xxxxxxxxxx>
> > Date:   Mon Dec 4 15:07:16 2017 +0100
> > 
> >     x86/kasan/64: Teach KASAN about the cpu_entry_area  
> 
> 
> Thanks.
> There is nothing wrong with this patch, it just uncovered older bug.
> The actual problem comes from f06bdd4001c2 ("x86/mm: Adapt MODULES_END based on fixmap section size")
> which is made kasan_mem_to_shadow(MODULES_END) potentially unaligned to page boundary.
> And when we feed unaligned address to kasan_populate_zero_shadow() it doesn't do the right thing.
> 
> Could you tell me if the fix bellow works for you?

Works for me, thank you!

Tested-by: Jakub Kicinski <jakub.kicinski@xxxxxxxxxxxxx>

>  arch/x86/include/asm/kasan.h            | 8 ++++++++
>  arch/x86/include/asm/pgtable_64_types.h | 4 +++-
>  2 files changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/include/asm/kasan.h b/arch/x86/include/asm/kasan.h
> index b577dd0916aa..0c580e4b2ccc 100644
> --- a/arch/x86/include/asm/kasan.h
> +++ b/arch/x86/include/asm/kasan.h
> @@ -5,6 +5,14 @@
>  #include <linux/const.h>
>  #define KASAN_SHADOW_OFFSET _AC(CONFIG_KASAN_SHADOW_OFFSET, UL)
>  
> +#ifndef KASAN_SHADOW_SCALE_SHIFT
> +# ifdef CONFIG_KASAN
> +#  define KASAN_SHADOW_SCALE_SHIFT 3
> +# else
> +#  define KASAN_SHADOW_SCALE_SHIFT 0
> +# endif
> +#endif
> +
>  /*
>   * Compiler uses shadow offset assuming that addresses start
>   * from 0. Kernel addresses don't start from 0, so shadow
> diff --git a/arch/x86/include/asm/pgtable_64_types.h b/arch/x86/include/asm/pgtable_64_types.h
> index 6d5f45dcd4a1..d34a90d6c374 100644
> --- a/arch/x86/include/asm/pgtable_64_types.h
> +++ b/arch/x86/include/asm/pgtable_64_types.h
> @@ -6,6 +6,7 @@
>  
>  #ifndef __ASSEMBLY__
>  #include <linux/types.h>
> +#include <asm/kasan.h>
>  #include <asm/kaslr.h>
>  
>  /*
> @@ -96,7 +97,8 @@ typedef struct { pteval_t pte; } pte_t;
>  #define VMALLOC_END	(VMALLOC_START + _AC((VMALLOC_SIZE_TB << 40) - 1, UL))
>  #define MODULES_VADDR    (__START_KERNEL_map + KERNEL_IMAGE_SIZE)
>  /* The module sections ends with the start of the fixmap */
> -#define MODULES_END   __fix_to_virt(__end_of_fixed_addresses + 1)
> +#define MODULES_END   (__fix_to_virt(__end_of_fixed_addresses + 1) & \
> +			~((PAGE_SIZE << KASAN_SHADOW_SCALE_SHIFT) - 1))
>  #define MODULES_LEN   (MODULES_END - MODULES_VADDR)
>  #define ESPFIX_PGD_ENTRY _AC(-2, UL)
>  #define ESPFIX_BASE_ADDR (ESPFIX_PGD_ENTRY << P4D_SHIFT)