Messages in this thread | | | Subject | Re: [PATCH 10/10] powerpc: remove address space overrides using set_fs() | From | Christophe Leroy <> | Date | Wed, 2 Sep 2020 16:12:50 +0200 |
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Le 02/09/2020 à 15:51, David Laight a écrit : > From: Christophe Leroy >> Sent: 02 September 2020 14:25 >> Le 02/09/2020 à 15:13, David Laight a écrit : >>> From: Christoph Hellwig >>>> Sent: 02 September 2020 13:37 >>>> >>>> On Wed, Sep 02, 2020 at 08:15:12AM +0200, Christophe Leroy wrote: >>>>>> - return 0; >>>>>> - return (size == 0 || size - 1 <= seg.seg - addr); >>>>>> + if (addr >= TASK_SIZE_MAX) >>>>>> + return false; >>>>>> + if (size == 0) >>>>>> + return false; >>>>> >>>>> __access_ok() was returning true when size == 0 up to now. Any reason to >>>>> return false now ? >>>> >>>> No, this is accidental and broken. Can you re-run your benchmark with >>>> this fixed? >>> >>> Is TASK_SIZE_MASK defined such that you can do: >>> >>> return (addr | size) < TASK_SIZE_MAX) || !size; >> >> TASK_SIZE_MAX will usually be 0xc0000000 >> >> With: >> addr = 0x80000000; >> size = 0x80000000; >> >> I expect it to fail .... >> >> With the formula you propose it will succeed, won't it ? > > Hmmm... Was i getting confused about some comments for 64bit > about there being such a big hole between valid user and kernel > addresses that it was enough to check that 'size < TASK_SIZE_MAX'. > > That would be true for 64bit x86 (and probably ppc (& arm??)) > if TASK_SIZE_MAX were 0x4 << 60. > IIUC the highest user address is (much) less than 0x0 << 60 > and the lowest kernel address (much) greater than 0xf << 60 > on all these 64bit platforms. > > Actually if doing access_ok() inside get_user() you don't > need to check the size at all.
You mean on 64 bit or on any platform ?
What about a word write to 0xbffffffe, won't it overwrite 0xc0000000 ?
> You don't even need to in copy_to/from_user() provided > it always does a forwards copy.
Do you mean due to the gap ? Is it garantied to be a gap ? Even on a 32 bits having TASK_SIZE set to 0xc0000000 and PAGE_OFFSET set to the same ?
Christophe
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