lkml.org 
[lkml]   [2020]   [Sep]   [8]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH v1 1/5] powerpc/mm: sanity_check_fault() should work for all, not only BOOK3S
From
Date


Le 08/09/2020 à 10:43, Nicholas Piggin a écrit :
> Excerpts from Christophe Leroy's message of August 7, 2020 3:15 am:
>> The verification and message introduced by commit 374f3f5979f9
>> ("powerpc/mm/hash: Handle user access of kernel address gracefully")
>> applies to all platforms, it should not be limited to BOOK3S.
>>
>> Make the BOOK3S version of sanity_check_fault() the one for all,
>> and bail out earlier if not BOOK3S.
>>
>> Fixes: 374f3f5979f9 ("powerpc/mm/hash: Handle user access of kernel address gracefully")
>> Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
>> ---
>> arch/powerpc/mm/fault.c | 8 +++-----
>> 1 file changed, 3 insertions(+), 5 deletions(-)
>>
>> diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
>> index 925a7231abb3..2efa34d7e644 100644
>> --- a/arch/powerpc/mm/fault.c
>> +++ b/arch/powerpc/mm/fault.c
>> @@ -303,7 +303,6 @@ static inline void cmo_account_page_fault(void)
>> static inline void cmo_account_page_fault(void) { }
>> #endif /* CONFIG_PPC_SMLPAR */
>>
>> -#ifdef CONFIG_PPC_BOOK3S
>> static void sanity_check_fault(bool is_write, bool is_user,
>> unsigned long error_code, unsigned long address)
>> {
>> @@ -320,6 +319,9 @@ static void sanity_check_fault(bool is_write, bool is_user,
>> return;
>> }
>>
>> + if (!IS_ENABLED(CONFIG_PPC_BOOK3S))
>> + return;
>
> Seems okay. Why is address == -1 special though? I guess it's because
> it may not be an exploit kernel reference but a buggy pointer underflow?
> In that case -1 doesn't seem like it would catch very much. Would it be
> better to test for high bit set for example ((long)address < 0) ?

See
https://github.com/linuxppc/linux/commit/0f9aee0cb9da7db7d96f63cfa2dc5e4f1bffeb87#diff-f9658f412252f3bb3093e0a95b37f3ac

-1 is what mmap() returns on error, if the app uses that as a pointer
that's a programming error not an exploit.

Euh .. If you test (long)address < 0, then the entire kernel falls into
that range as usually it goes from 0xc0000000 to 0xffffffff

But we could skip the top page entirely, anyway it is never mapped.

>
> Anyway for your patch
>
> Reviewed-by: Nicholas Piggin <npiggin@gmail.com>

Thanks
Christophe

\
 
 \ /
  Last update: 2020-09-08 10:57    [W:0.333 / U:0.556 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site