Re: [PATCH v2] drm/ttm: fix one use-after-free

[Lang Yu <Lang.Yu@amd.com>]

On 07/05/ , Matthew Auld wrote:
> On Wed, 5 Jul 2023 at 11:08, Lang Yu <Lang.Yu@amd.com> wrote:
> >
> > bo->kref is increased once(kref_init()) in ttm_bo_release,
> > but decreased twice(ttm_bo_put()) respectively in
> > ttm_bo_delayed_delete and ttm_bo_cleanup_refs,
> > which is unbalanced.
> >
> > Just clean up bo resource in one place for a delayed deleted bo.
> >
> > Fixes: 9bff18d13473 ("drm/ttm: use per BO cleanup workers")
> >
> > [   67.399887] refcount_t: underflow; use-after-free.
> > [   67.399901] WARNING: CPU: 0 PID: 3172 at lib/refcount.c:28 refcount_warn_saturate+0xc2/0x110
> > [   67.400124] RIP: 0010:refcount_warn_saturate+0xc2/0x110
> > [   67.400173] Call Trace:
> > [   67.400176]  <TASK>
> > [   67.400181]  ttm_mem_evict_first+0x4fe/0x5b0 [ttm]
> > [   67.400216]  ttm_bo_mem_space+0x1e3/0x240 [ttm]
> > [   67.400239]  ttm_bo_validate+0xc7/0x190 [ttm]
> > [   67.400253]  ? ww_mutex_trylock+0x1b1/0x390
> > [   67.400266]  ttm_bo_init_reserved+0x183/0x1c0 [ttm]
> > [   67.400280]  ? __rwlock_init+0x3d/0x70
> > [   67.400292]  amdgpu_bo_create+0x1cd/0x4f0 [amdgpu]
> > [   67.400607]  ? __pfx_amdgpu_bo_user_destroy+0x10/0x10 [amdgpu]
> > [   67.400980]  amdgpu_bo_create_user+0x38/0x70 [amdgpu]
> > [   67.401291]  amdgpu_gem_object_create+0x77/0xb0 [amdgpu]
> > [   67.401641]  ? __pfx_amdgpu_bo_user_destroy+0x10/0x10 [amdgpu]
> > [   67.401958]  amdgpu_amdkfd_gpuvm_alloc_memory_of_gpu+0x228/0xa30 [amdgpu]
> > [   67.402433]  kfd_ioctl_alloc_memory_of_gpu+0x14e/0x390 [amdgpu]
> > [   67.402824]  ? lock_release+0x13f/0x290
> > [   67.402838]  kfd_ioctl+0x1e0/0x640 [amdgpu]
> > [   67.403205]  ? __pfx_kfd_ioctl_alloc_memory_of_gpu+0x10/0x10 [amdgpu]
> > [   67.403579]  ? tomoyo_file_ioctl+0x19/0x20
> > [   67.403590]  __x64_sys_ioctl+0x95/0xd0
> > [   67.403601]  do_syscall_64+0x3b/0x90
> > [   67.403609]  entry_SYSCALL_64_after_hwframe+0x72/0xdc
> >
> > Signed-off-by: Lang Yu <Lang.Yu@amd.com>
> > ---
> >  drivers/gpu/drm/ttm/ttm_bo.c | 89 ++++--------------------------------
> >  1 file changed, 10 insertions(+), 79 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
> > index 326a3d13a829..1e073dfb1332 100644
> > --- a/drivers/gpu/drm/ttm/ttm_bo.c
> > +++ b/drivers/gpu/drm/ttm/ttm_bo.c
> > @@ -224,82 +224,6 @@ static void ttm_bo_flush_all_fences(struct ttm_buffer_object *bo)
> >         dma_resv_iter_end(&cursor);
> >  }
> >
> > -/**
> > - * ttm_bo_cleanup_refs
> > - * If bo idle, remove from lru lists, and unref.
> > - * If not idle, block if possible.
> > - *
> > - * Must be called with lru_lock and reservation held, this function
> > - * will drop the lru lock and optionally the reservation lock before returning.
> > - *
> > - * @bo:                    The buffer object to clean-up
> > - * @interruptible:         Any sleeps should occur interruptibly.
> > - * @no_wait_gpu:           Never wait for gpu. Return -EBUSY instead.
> > - * @unlock_resv:           Unlock the reservation lock as well.
> > - */
> > -
> > -static int ttm_bo_cleanup_refs(struct ttm_buffer_object *bo,
> > -                              bool interruptible, bool no_wait_gpu,
> > -                              bool unlock_resv)
> > -{
> > -       struct dma_resv *resv = &bo->base._resv;
> > -       int ret;
> > -
> > -       if (dma_resv_test_signaled(resv, DMA_RESV_USAGE_BOOKKEEP))
> > -               ret = 0;
> > -       else
> > -               ret = -EBUSY;
> > -
> > -       if (ret && !no_wait_gpu) {
> > -               long lret;
> > -
> > -               if (unlock_resv)
> > -                       dma_resv_unlock(bo->base.resv);
> > -               spin_unlock(&bo->bdev->lru_lock);
> > -
> > -               lret = dma_resv_wait_timeout(resv, DMA_RESV_USAGE_BOOKKEEP,
> > -                                            interruptible,
> > -                                            30 * HZ);
> > -
> > -               if (lret < 0)
> > -                       return lret;
> > -               else if (lret == 0)
> > -                       return -EBUSY;
> > -
> > -               spin_lock(&bo->bdev->lru_lock);
> > -               if (unlock_resv && !dma_resv_trylock(bo->base.resv)) {
> > -                       /*
> > -                        * We raced, and lost, someone else holds the reservation now,
> > -                        * and is probably busy in ttm_bo_cleanup_memtype_use.
> > -                        *
> > -                        * Even if it's not the case, because we finished waiting any
> > -                        * delayed destruction would succeed, so just return success
> > -                        * here.
> > -                        */
> > -                       spin_unlock(&bo->bdev->lru_lock);
> > -                       return 0;
> > -               }
> > -               ret = 0;
> > -       }
> > -
> > -       if (ret) {
> > -               if (unlock_resv)
> > -                       dma_resv_unlock(bo->base.resv);
> > -               spin_unlock(&bo->bdev->lru_lock);
> > -               return ret;
> > -       }
> > -
> > -       spin_unlock(&bo->bdev->lru_lock);
> > -       ttm_bo_cleanup_memtype_use(bo);
> > -
> > -       if (unlock_resv)
> > -               dma_resv_unlock(bo->base.resv);
> > -
> > -       ttm_bo_put(bo);
> 
> The put() here is indeed broken and leads to some nasty uaf I think,
> but we fixed that a while back in: c00133a9e87e ("drm/ttm: drop extra
> ttm_bo_put in ttm_bo_cleanup_refs"). It looks like you are using an
> old tree? Perhaps the issue you are seeing was also fixed with that?

Thanks. I can see this commit in my tree but it was overrode by other
patches. It fixed this issue.

Regards,
Lang

> > -
> > -       return 0;
> > -}
> > -
> >  /*
> >   * Block for the dma_resv object to become idle, lock the buffer and clean up
> >   * the resource and tt object.
> > @@ -622,8 +546,10 @@ int ttm_mem_evict_first(struct ttm_device *bdev,
> >         }
> >
> >         if (bo->deleted) {
> > -               ret = ttm_bo_cleanup_refs(bo, ctx->interruptible,
> > -                                         ctx->no_wait_gpu, locked);
> > +               if (locked)
> > +                       dma_resv_unlock(bo->base.resv);
> > +               spin_unlock(&bdev->lru_lock);
> > +               ret = ttm_bo_wait_ctx(bo, ctx);
> >                 ttm_bo_put(bo);
> >                 return ret;
> >         }
> > @@ -1146,7 +1072,12 @@ int ttm_bo_swapout(struct ttm_buffer_object *bo, struct ttm_operation_ctx *ctx,
> >         }
> >
> >         if (bo->deleted) {
> > -               ret = ttm_bo_cleanup_refs(bo, false, false, locked);
> > +               struct ttm_operation_ctx ctx = { false, false };
> > +
> > +               if (locked)
> > +                       dma_resv_unlock(bo->base.resv);
> > +               spin_unlock(&bo->bdev->lru_lock);
> > +               ret = ttm_bo_wait_ctx(bo, &ctx);
> >                 ttm_bo_put(bo);
> >                 return ret == -EBUSY ? -ENOSPC : ret;
> >         }
> > --
> > 2.25.1
> >