On Mon, Jul 01, 2024 at 10:50:38AM GMT, Ekansh Gupta wrote: > > > On 6/28/2024 7:51 PM, Greg KH wrote: > > On Fri, Jun 28, 2024 at 04:12:10PM +0530, Ekansh Gupta wrote: > >> > >> On 6/28/2024 3:59 PM, Ekansh Gupta wrote: > >>> On 6/27/2024 4:43 PM, Dmitry Baryshkov wrote: > >>>> On Thu, Jun 27, 2024 at 11:35:18AM GMT, Ekansh Gupta wrote: > >>>>> For user PD initialization, initmem is allocated and sent to DSP for > >>>>> initial memory requirements like shell loading. This size is passed > >>>>> by user space and is checked against a max size. For unsigned PD > >>>>> offloading, more than 2MB size could be passed by user which would > >>>>> result in PD initialization failure. Remove the user PD initmem size > >>>>> check and allow buffer allocation for user passed size. Any additional > >>>>> memory sent to DSP during PD init is used as the PD heap. > >>>> Would it allow malicious userspace to allocate big enough buffers and > >>>> reduce the amount of memory available to the system? To other DSP > >>>> programs? > >>> The allocation here is happening from SMMU context bank which is uniquely assigned > >>> to processes going to DSP. As per my understanding process can allocate maximum > >>> 4GB of memory from the context bank and the memory availability will be taken care > >>> by kernel memory management. Please correct me if my understanding is incorrect. > >> Just wanted to add 1 question here: > >> User space can also directly allocate memory. Wouldn't that be a problem if any malicious userspace > >> allocated huge memory? > > No, because any userspace program that takes up too much memory will be > > killed by the kernel. > > > > You can not have userspace tell the kernel to allocate 100Gb of memory, > > as then the kernel is the one that just took it all up, and then > > userspace applications will start to be killed off. > > > > You MUST bounds check your userspace-supplied memory requests. Remember > > the 4 words of kernel development: > > > > All input is evil. > Thanks for the detailed explanation, Greg. I'll remember this going forward. > > For this change, I'll increase the max size limit to 5MB which is the requirement for > unsigned PD to run on DSP. So we are back to the quesiton of why 5MB is considered to be enough, see https://lore.kernel.org/linux-arm-msm/2024061755-snare-french-de38@gregkh/ > > --Ekansh > > thanks, > > > > greg k-h > -- With best wishes Dmitry
