[PATCH] powerpc/32: disable KASAN with pages bigger than 16k

[PATCH] powerpc/32: disable KASAN with pages bigger than 16k

[Christophe Leroy]

Mapping of early shadow area is implemented by using a single static
page table having all entries pointing to the same early shadow page.
The shadow area must therefore occupy full PGD entries.

The shadow area has a size of 128Mbytes starting at 0xf8000000.
With 4k pages, a PGD entry is 4Mbytes
With 16k pages, a PGD entry is 64Mbytes
With 64k pages, a PGD entry is 256Mbytes which is too big.

Until we rework the early shadow mapping, disable KASAN when the
page size is too big.

Reported-by: kbuild test robot <lkp@intel.com>
Fixes: 2edb16efc899 ("powerpc/32: Add KASAN support")
Cc: stable@vger.kernel.org
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
---
 arch/powerpc/Kconfig | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 1dfa59126fcf..066b36bf9efa 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -169,8 +169,8 @@ config PPC
 	select HAVE_ARCH_AUDITSYSCALL
 	select HAVE_ARCH_HUGE_VMAP		if PPC_BOOK3S_64 && PPC_RADIX_MMU
 	select HAVE_ARCH_JUMP_LABEL
-	select HAVE_ARCH_KASAN			if PPC32
-	select HAVE_ARCH_KASAN_VMALLOC		if PPC32
+	select HAVE_ARCH_KASAN			if PPC32 && PPC_PAGE_SHIFT <= 14
+	select HAVE_ARCH_KASAN_VMALLOC		if PPC32 && PPC_PAGE_SHIFT <= 14
 	select HAVE_ARCH_KGDB
 	select HAVE_ARCH_MMAP_RND_BITS
 	select HAVE_ARCH_MMAP_RND_COMPAT_BITS	if COMPAT
-- 
2.25.0

Re: [PATCH] powerpc/32: disable KASAN with pages bigger than 16k

[Christophe Leroy]

Le 28/05/2020 à 12:17, Christophe Leroy a écrit :
> Mapping of early shadow area is implemented by using a single static
> page table having all entries pointing to the same early shadow page.
> The shadow area must therefore occupy full PGD entries.
> 
> The shadow area has a size of 128Mbytes starting at 0xf8000000.
> With 4k pages, a PGD entry is 4Mbytes
> With 16k pages, a PGD entry is 64Mbytes
> With 64k pages, a PGD entry is 256Mbytes which is too big.

That's for 32k pages that a PGD is 256Mbytes.

With 64k pages, a PGD entry is 1Gbytes which is too big.

Michael, can you fix the commit log ?

Thanks
Christophe

> 
> Until we rework the early shadow mapping, disable KASAN when the
> page size is too big.
> 
> Reported-by: kbuild test robot <lkp@intel.com>
> Fixes: 2edb16efc899 ("powerpc/32: Add KASAN support")
> Cc: stable@vger.kernel.org
> Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
> ---
>   arch/powerpc/Kconfig | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index 1dfa59126fcf..066b36bf9efa 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -169,8 +169,8 @@ config PPC
>   	select HAVE_ARCH_AUDITSYSCALL
>   	select HAVE_ARCH_HUGE_VMAP		if PPC_BOOK3S_64 && PPC_RADIX_MMU
>   	select HAVE_ARCH_JUMP_LABEL
> -	select HAVE_ARCH_KASAN			if PPC32
> -	select HAVE_ARCH_KASAN_VMALLOC		if PPC32
> +	select HAVE_ARCH_KASAN			if PPC32 && PPC_PAGE_SHIFT <= 14
> +	select HAVE_ARCH_KASAN_VMALLOC		if PPC32 && PPC_PAGE_SHIFT <= 14
>   	select HAVE_ARCH_KGDB
>   	select HAVE_ARCH_MMAP_RND_BITS
>   	select HAVE_ARCH_MMAP_RND_COMPAT_BITS	if COMPAT
> 

Re: [PATCH] powerpc/32: disable KASAN with pages bigger than 16k

[Michael Ellerman]

Christophe Leroy <christophe.leroy@csgroup.eu> writes:
> Le 28/05/2020 à 12:17, Christophe Leroy a écrit :
>> Mapping of early shadow area is implemented by using a single static
>> page table having all entries pointing to the same early shadow page.
>> The shadow area must therefore occupy full PGD entries.
>> 
>> The shadow area has a size of 128Mbytes starting at 0xf8000000.
>> With 4k pages, a PGD entry is 4Mbytes
>> With 16k pages, a PGD entry is 64Mbytes
>> With 64k pages, a PGD entry is 256Mbytes which is too big.
>
> That's for 32k pages that a PGD is 256Mbytes.
>
> With 64k pages, a PGD entry is 1Gbytes which is too big.
>
> Michael, can you fix the commit log ?

Yes.

  powerpc/32: Disable KASAN with pages bigger than 16k
  
  Mapping of early shadow area is implemented by using a single static
  page table having all entries pointing to the same early shadow page.
  The shadow area must therefore occupy full PGD entries.
  
  The shadow area has a size of 128MB starting at 0xf8000000.
  With 4k pages, a PGD entry is 4MB
  With 16k pages, a PGD entry is 64MB
  With 64k pages, a PGD entry is 1GB which is too big.
  
  Until we rework the early shadow mapping, disable KASAN when the page
  size is too big.

  Fixes: 2edb16efc899 ("powerpc/32: Add KASAN support")
  Cc: stable@vger.kernel.org # v5.2+
  Reported-by: kbuild test robot <lkp@intel.com>
  Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
  Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
  Link: https://lore.kernel.org/r/7195fcde7314ccbf7a081b356084a69d421b10d4.1590660977.git.christophe.leroy@csgroup.eu


cheers

Re: [PATCH] powerpc/32: disable KASAN with pages bigger than 16k

[Michael Ellerman]

On Thu, 28 May 2020 10:17:04 +0000 (UTC), Christophe Leroy wrote:
> Mapping of early shadow area is implemented by using a single static
> page table having all entries pointing to the same early shadow page.
> The shadow area must therefore occupy full PGD entries.
> 
> The shadow area has a size of 128Mbytes starting at 0xf8000000.
> With 4k pages, a PGD entry is 4Mbytes
> With 16k pages, a PGD entry is 64Mbytes
> With 64k pages, a PGD entry is 256Mbytes which is too big.
> 
> [...]

Applied to powerpc/next.

[1/1] powerpc/32: Disable KASAN with pages bigger than 16k
      https://git.kernel.org/powerpc/c/888468ce725a4cd56d72dc7e5096078f7a9251a0

cheers