On 12/16/2022 9:09 AM, Jason Gunthorpe wrote:
> On Thu, Dec 15, 2022 at 01:56:59PM -0800, Steve Sistare wrote:
>> When a vfio container is preserved across exec, the task does not change,
>> but it gets a new mm with locked_vm=0. If the user later unmaps a dma
>> mapping, locked_vm underflows to a large unsigned value, and a subsequent
>> dma map request fails with ENOMEM in __account_locked_vm.
>>
>> To avoid underflow, grab and save the mm at the time a dma is mapped.
>> Use that mm when adjusting locked_vm, rather than re-acquiring the saved
>> task's mm, which may have changed. If the saved mm is dead, do nothing.
>>
>> Signed-off-by: Steve Sistare <steven.sistare@xxxxxxxxxx>
>> ---
>> drivers/vfio/vfio_iommu_type1.c | 17 ++++++++++-------
>> 1 file changed, 10 insertions(+), 7 deletions(-)
>
> Add fixes lines and a CC stable
This predates the update vaddr functionality, so AFAICT:
Fixes: 73fa0d10d077 ("vfio: Type1 IOMMU implementation")
I'll wait on cc'ing stable until alex has chimed in.
> The subject should be more like 'vfio/typ1: Prevent corruption of mm->locked_vm via exec()'
Underflow is a more precise description of the first corruption. How about:
vfio/type1: Prevent underflow of locked_vm via exec()
>> @@ -1687,6 +1689,8 @@ static int vfio_dma_do_map(struct vfio_iommu *iommu,
>> get_task_struct(current->group_leader);
>> dma->task = current->group_leader;
>> dma->lock_cap = capable(CAP_IPC_LOCK);
>> + dma->mm = dma->task->mm;
>
> This should be current->mm, current->group_leader->mm is not quite the
> same thing (and maybe another bug, I'm not sure)
When are they different -- when the leader is a zombie?
BTW I just noticed I need to update the comments about mm preceding these lines.
- Steve
