Re: [PATCH] drm/amdgpu: Fix a potential sdma invalid access

[Qu Huang <jinsdb@126.com>]

Hi Christian,

On 2021/4/3 0:25, Christian König wrote:
> Hi Qu,
> 
> Am 02.04.21 um 05:18 schrieb Qu Huang:
>> Before dma_resv_lock(bo->base.resv, NULL) in amdgpu_bo_release_notify(),
>> the bo->base.resv lock may be held by ttm_mem_evict_first(),
> 
> That can't happen since when bo_release_notify is called the BO has not 
> more references and is therefore deleted.
> 
> And we never evict a deleted BO, we just wait for it to become idle.

Yes, the bo reference counter return to zero will enter 
ttm_bo_release(),but notify bo release (call amdgpu_bo_release_notify()) 
first happen, and then test if a reservation object's fences have been 
signaled, and then mark bo as deleted and remove bo from the LRU list.

When ttm_bo_release() and ttm_mem_evict_first() is concurrent,
the Bo has not been removed from the LRU list and is not marked as 
deleted, this will happen.

As a test, when we use CPU memset instead of SDMA fill in 
amdgpu_bo_release_notify(), the result is page fault:

PID: 5490   TASK: ffff8e8136e04100  CPU: 4   COMMAND: "gemmPerf"
  #0 [ffff8e79eaa17970] machine_kexec at ffffffffb2863784
  #1 [ffff8e79eaa179d0] __crash_kexec at ffffffffb291ce92
  #2 [ffff8e79eaa17aa0] crash_kexec at ffffffffb291cf80
  #3 [ffff8e79eaa17ab8] oops_end at ffffffffb2f6c768
  #4 [ffff8e79eaa17ae0] no_context at ffffffffb2f5aaa6
  #5 [ffff8e79eaa17b30] __bad_area_nosemaphore at ffffffffb2f5ab3d
  #6 [ffff8e79eaa17b80] bad_area_nosemaphore at ffffffffb2f5acae
  #7 [ffff8e79eaa17b90] __do_page_fault at ffffffffb2f6f6c0
  #8 [ffff8e79eaa17c00] do_page_fault at ffffffffb2f6f925
  #9 [ffff8e79eaa17c30] page_fault at ffffffffb2f6b758
     [exception RIP: memset+31]
     RIP: ffffffffb2b8668f  RSP: ffff8e79eaa17ce8  RFLAGS: 00010a17
     RAX: bebebebebebebebe  RBX: ffff8e747bff10c0  RCX: 0000060b00200000
     RDX: 0000000000000000  RSI: 00000000000000be  RDI: ffffab807f000000
     RBP: ffff8e79eaa17d10   R8: ffff8e79eaa14000   R9: ffffab7c80000000
     R10: 000000000000bcba  R11: 00000000000001ba  R12: ffff8e79ebaa4050
     R13: ffffab7c80000000  R14: 0000000000022600  R15: ffff8e8136e04100
     ORIG_RAX: ffffffffffffffff  CS: 0010  SS: 0018
#10 [ffff8e79eaa17ce8] amdgpu_bo_release_notify at ffffffffc092f2d1 [amdgpu]
#11 [ffff8e79eaa17d18] ttm_bo_release at ffffffffc08f39dd [amdttm]
#12 [ffff8e79eaa17d58] amdttm_bo_put at ffffffffc08f3c8c [amdttm]
#13 [ffff8e79eaa17d68] amdttm_bo_vm_close at ffffffffc08f7ac9 [amdttm]
#14 [ffff8e79eaa17d80] remove_vma at ffffffffb29ef115
#15 [ffff8e79eaa17da0] exit_mmap at ffffffffb29f2c64
#16 [ffff8e79eaa17e58] mmput at ffffffffb28940c7
#17 [ffff8e79eaa17e78] do_exit at ffffffffb289dc95
#18 [ffff8e79eaa17f10] do_group_exit at ffffffffb289e4cf
#19 [ffff8e79eaa17f40] sys_exit_group at ffffffffb289e544
#20 [ffff8e79eaa17f50] system_call_fastpath at ffffffffb2f74ddb

Regards,
Qu.


> 
> Regards,
> Christian.
> 
>> and the VRAM mem will be evicted, mem region was replaced
>> by Gtt mem region. amdgpu_bo_release_notify() will then
>> hold the bo->base.resv lock, and SDMA will get an invalid
>> address in amdgpu_fill_buffer(), resulting in a VMFAULT
>> or memory corruption.
>>
>> To avoid it, we have to hold bo->base.resv lock first, and
>> check whether the mem.mem_type is TTM_PL_VRAM.
>>
>> Signed-off-by: Qu Huang <jinsdb@126.com>
>> ---
>>   drivers/gpu/drm/amd/amdgpu/amdgpu_object.c | 8 ++++++--
>>   1 file changed, 6 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c 
>> b/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c
>> index 4b29b82..8018574 100644
>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c
>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c
>> @@ -1300,12 +1300,16 @@ void amdgpu_bo_release_notify(struct 
>> ttm_buffer_object *bo)
>>       if (bo->base.resv == &bo->base._resv)
>>           amdgpu_amdkfd_remove_fence_on_pt_pd_bos(abo);
>>
>> -    if (bo->mem.mem_type != TTM_PL_VRAM || !bo->mem.mm_node ||
>> -        !(abo->flags & AMDGPU_GEM_CREATE_VRAM_WIPE_ON_RELEASE))
>> +    if (!(abo->flags & AMDGPU_GEM_CREATE_VRAM_WIPE_ON_RELEASE))
>>           return;
>>
>>       dma_resv_lock(bo->base.resv, NULL);
>>
>> +    if (bo->mem.mem_type != TTM_PL_VRAM || !bo->mem.mm_node) {
>> +        dma_resv_unlock(bo->base.resv);
>> +        return;
>> +    }
>> +
>>       r = amdgpu_fill_buffer(abo, AMDGPU_POISON, bo->base.resv, &fence);
>>       if (!WARN_ON(r)) {
>>           amdgpu_bo_fence(abo, fence, false);
>> -- 
>> 1.8.3.1
>>

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