Re: [PATCH] drm/tegra: Check offsets of a submitted command buffer and of relocations

[Dmitry Osipenko <digetx-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

On 16.05.2017 11:10, Mikko Perttunen wrote:
> 
> 
> On 16.05.2017 10:32, Erik Faye-Lund wrote:
>> On Tue, May 16, 2017 at 8:56 AM, Mikko Perttunen <cyndis-/1wQRMveznE@public.gmane.org> wrote:
>>> On 14.05.2017 23:47, Dmitry Osipenko wrote:
>>>>
>>>> If commands buffer claims a number of words that is higher than its BO can
>>>> fit, a kernel OOPS will be fired on the out-of-bounds BO access. This was
>>>> triggered by an opentegra Xorg driver that erroneously pushed too many
>>>> commands to the pushbuf. The CMDA commands buffer address is 4 bytes
>>>> aligned, so check the alignment as well.
>>>>
>>>> Add a sanity check for the relocations in a same way.
>>>>
>>>> [   46.829393] Unable to handle kernel paging request at virtual address
>>>> f09b2000
>>>> ...
>>>> [<c04a3ba4>] (host1x_job_pin) from [<c04dfcd0>]
>>>> (tegra_drm_submit+0x474/0x510)
>>>> [<c04dfcd0>] (tegra_drm_submit) from [<c04deea0>] (tegra_submit+0x50/0x6c)
>>>> [<c04deea0>] (tegra_submit) from [<c04c07c0>] (drm_ioctl+0x1e4/0x3ec)
>>>> [<c04c07c0>] (drm_ioctl) from [<c02541a0>] (do_vfs_ioctl+0x9c/0x8e4)
>>>> [<c02541a0>] (do_vfs_ioctl) from [<c0254a1c>] (SyS_ioctl+0x34/0x5c)
>>>> [<c0254a1c>] (SyS_ioctl) from [<c0107640>] (ret_fast_syscall+0x0/0x3c)
>>>>
>>>> Signed-off-by: Dmitry Osipenko <digetx-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
>>>> Reviewed-by: Erik Faye-Lund <kusmabite-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
>>>> ---
>>>>  drivers/gpu/drm/tegra/drm.c | 30 ++++++++++++++++++++++++++++++
>>>>  drivers/gpu/drm/tegra/gem.c |  5 -----
>>>>  drivers/gpu/drm/tegra/gem.h |  5 +++++
>>>>  3 files changed, 35 insertions(+), 5 deletions(-)
>>>>
>>>> diff --git a/drivers/gpu/drm/tegra/drm.c b/drivers/gpu/drm/tegra/drm.c
>>>> index 768750226452..c5844a065681 100644
>>>> --- a/drivers/gpu/drm/tegra/drm.c
>>>> +++ b/drivers/gpu/drm/tegra/drm.c
>>>> @@ -362,6 +362,8 @@ int tegra_drm_submit(struct tegra_drm_context
>>>> *context,
>>>>         while (num_cmdbufs) {
>>>>                 struct drm_tegra_cmdbuf cmdbuf;
>>>>                 struct host1x_bo *bo;
>>>> +               struct tegra_bo *obj;
>>>> +               u64 offset;
>>>>
>>>>                 if (copy_from_user(&cmdbuf, cmdbufs, sizeof(cmdbuf))) {
>>>>                         err = -EFAULT;
>>>> @@ -374,6 +376,14 @@ int tegra_drm_submit(struct tegra_drm_context
>>>> *context,
>>>>                         goto fail;
>>>>                 }
>>>>
>>>> +               offset = (u64)cmdbuf.offset + (u64)cmdbuf.words *
>>>> sizeof(u32);
>>>> +               obj = host1x_to_tegra_bo(bo);
>>>> +
>>>> +               if (offset & 3 || offset > obj->gem.size) {
>>>> +                       err = -EINVAL;
>>>> +                       goto fail;
>>>> +               }
>>>> +
>>>>                 host1x_job_add_gather(job, bo, cmdbuf.words,
>>>> cmdbuf.offset);
>>>>                 num_cmdbufs--;
>>>>                 cmdbufs++;
>>>> @@ -381,11 +391,31 @@ int tegra_drm_submit(struct tegra_drm_context
>>>> *context,
>>>>
>>>>         /* copy and resolve relocations from submit */
>>>>         while (num_relocs--) {
>>>> +               struct host1x_reloc *reloc;
>>>> +               struct tegra_bo *obj;
>>>> +
>>>>                 err =
>>>> host1x_reloc_copy_from_user(&job->relocarray[num_relocs],
>>>>                                                   &relocs[num_relocs],
>>>> drm,
>>>>                                                   file);
>>>>                 if (err < 0)
>>>>                         goto fail;
>>>> +
>>>> +               reloc = &job->relocarray[num_relocs];
>>>> +               obj = host1x_to_tegra_bo(reloc->cmdbuf.bo);
>>>> +
>>>> +               if (reloc->cmdbuf.offset & 3 ||
>>>> +                   reloc->cmdbuf.offset > obj->gem.size) {
>>>
>>>
>>> This could still fail if the bo's size is not divisible by 4, even with >=
>>> comparison (we would overwrite the buffer by 1 to 3 bytes). I would do the
>>> same as in the gather case, i.e. find out the address immediately after the
>>> write and compare using >. Perhaps add a helper function if it makes sense.
>>> I also don't think the "& 3" checks are needed.
>>
>> The bo-size is always a multiple of PAGE_SIZE, due to the rounding in
>> tegra_bo_alloc_object(), so I don't think this actually can fail. But
>> maybe we want to future-proof this code for a potential future where
>> this is not the case?
>>
> 
> Yeah, I think whether or not this might change in the future, the code would be
> easier to understand with the change.

It's very unlikely to me that BO size round-upping may go away. I'll add a
comment for that alignment check to make it clear in the code.

-- 
Dmitry