On Thu, 17 Dec 2020 11:59:23 +0100, Lars-Peter Clausen wrote: > > On 12/17/20 10:55 AM, Takashi Iwai wrote: > > On Thu, 17 Dec 2020 10:43:45 +0100, > > Lars-Peter Clausen wrote: > >> On 12/17/20 5:15 PM, Robin Gong wrote: > >>> Since mmap for userspace is based on page alignment, add page alignment > >>> for iram alloc from pool, otherwise, some good data located in the same > >>> page of dmab->area maybe touched wrongly by userspace like pulseaudio. > >>> > >> I wonder, do we also have to align size to be a multiple of PAGE_SIZE > >> to avoid leaking unrelated data? > > Hm, a good question. Basically the PCM buffer size itself shouldn't > > be influenced by that (i.e. no hw-constraint or such is needed), but > > the padding should be cleared indeed. I somehow left those to the > > allocator side, but maybe it's safer to clear the whole buffer in > > sound/core/memalloc.c commonly. > > What I meant was that most of the APIs that we use to allocate memory > work on a PAGE_SIZE granularity. I.e. if you request a buffer that > where the size is not a multiple of PAGE_SIZE internally they will > still allocate a buffer that is a multiple of PAGE_SIZE and mark the > unused bytes as reserved. > > But I believe that is not the case gen_pool_dma_alloc(). It will > happily allocate those extra bytes to some other allocation request. > > That we need to zero out the reserved bytes even for those other APIs > is a very good additional point! > > I looked at this a few years ago and I'm pretty sure that we cleared > out the allocated area, but I can't find that anymore in the current > code. Which is not so great I guess. IIRC, we used GFP_ZERO in the past for the normal page allocations, but this was dropped as it's no longer supported or so. Also, we clear out the PCM buffer in hw_params call, but this is for the requested size, not the actual allocated size, hence the padding bytes will remain uncleared. So I believe it's safer to add an extra memset() like my test patch. Takashi
