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

[Erik Faye-Lund]

On Tue, May 16, 2017 at 8:56 AM, Mikko Perttunen <cyndis at kapsi.fi> 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 at gmail.com>
>> Reviewed-by: Erik Faye-Lund <kusmabite at gmail.com>
>> ---
>>  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?