[Intel-gfx] [PATCH] drm/i915: fix out-of-bounds page_table access

[Dave Gordon]

On 24/06/16 17:37, Chris Wilson wrote:
> On Fri, Jun 24, 2016 at 05:04:46PM +0100, Matthew Auld wrote:
>> The gen6_for_all_pdes macro does the upper-bound evaluation after
>> accessing the page_table array, hence on the final iteration we end up
>> hitting an out-of-bounds error:
>>
>> [ 1023.831657] UBSAN: Undefined behaviour in drivers/gpu/drm/i915/i915_gem_gtt.c:1993:2
>> [ 1023.831680] index 512 is out of range for type 'i915_page_table *[512]'
>> [ 1023.831696] CPU: 0 PID: 4833 Comm: rmmod Tainted: G     U          4.7.0-rc4-drm-intel-debug+ #5
>> [ 1023.831698] Hardware name: ASUS All Series/Z87-K, BIOS 1202 05/13/2014
>> [ 1023.831700]  0000000000000200 00000000adfe9733 ffff8801a3917988 ffffffff818cc0a4
>> [ 1023.831705]  0000000041b58ab3 ffffffff8275ca08 ffffffff818cbff2 ffff8801a39179b0
>> [ 1023.831708]  ffff8801a3917960 0000000000000200 1ffffffff4365b17 0000000000000001
>> [ 1023.831711] Call Trace:
>> [ 1023.831717]  [<ffffffff818cc0a4>] dump_stack+0xb2/0x10e
>> [ 1023.831721]  [<ffffffff818cbff2>] ? _atomic_dec_and_lock+0x152/0x152
>> [ 1023.831726]  [<ffffffff81952b0b>] ubsan_epilogue+0xd/0x4e
>> [ 1023.831730]  [<ffffffff8195373d>] __ubsan_handle_out_of_bounds+0x107/0x14d
>> [ 1023.831733]  [<ffffffff81953636>] ? __ubsan_handle_shift_out_of_bounds+0x24c/0x24c
>> [ 1023.831737]  [<ffffffff814bfde6>] ? kfree+0x246/0x3f0
>> [ 1023.831801]  [<ffffffffa183bff8>] gen6_ppgtt_cleanup+0x128/0x130 [i915]
>>
>> Cc: Chris Wilson <chris at chris-wilson.co.uk>
>> Signed-off-by: Matthew Auld <matthew.auld at intel.com>
>
> Ok. Tried to find something to complain about and couldn't.
> Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk>
> -Chris

Well ... not enough to reject it, but there's the lack of parentheses 
round macro parameters, and it uses ?: rather than the && style used in 
the Gen8 equivalents. I'll post an alternative based on the Gen8 version ...

.Dave.