On Thu, 17 Dec 2020 14:16:48 +0100,
Lars-Peter Clausen wrote:
On 12/17/20 12:06 PM, Takashi Iwai wrote:That's true. On the second though, it might be better to extend that
On Thu, 17 Dec 2020 11:59:23 +0100,Ah! That memset() in hw_params is new.
Lars-Peter Clausen wrote:
On 12/17/20 10:55 AM, Takashi Iwai wrote:IIRC, we used GFP_ZERO in the past for the normal page allocations,
On Thu, 17 Dec 2020 10:43:45 +0100,What I meant was that most of the APIs that we use to allocate memory
Lars-Peter Clausen wrote:
On 12/17/20 5:15 PM, Robin Gong wrote:Hm, a good question. Basically the PCM buffer size itself shouldn't
Since mmap for userspace is based on page alignment, add page alignmentI wonder, do we also have to align size to be a multiple of PAGE_SIZE
for iram alloc from pool, otherwise, some good data located in the same
page of dmab->area maybe touched wrongly by userspace like pulseaudio.
to avoid leaking unrelated data?
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.
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.
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.Yea, we definitely want that.
Do we care about leaking audio samples from a previous
application. I.e. application 'A' allocates a buffer plays back some
data and then closes the device again. Application 'B' then opens the
same audio devices allocates a slightly smaller buffer, so that it
still uses the same number of pages. The buffer from the previous
allocation get reused, but the remainder of the last page wont get
cleared in hw_params().
memset() in hw_params to assure clearing the whole allocated buffer.
We can check runtime->dma_buffer_p->bytes for the actual size.
Also, in the PCM memory allocator, we make sure that the allocation is
performed for page size.
diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c
index 47b155a49226..6aabad070abf 100644
--- a/sound/core/pcm_native.c
+++ b/sound/core/pcm_native.c
@@ -755,8 +755,15 @@ static int snd_pcm_hw_params(struct snd_pcm_substream *substream,
runtime->boundary *= 2;
/* clear the buffer for avoiding possible kernel info leaks */
- if (runtime->dma_area && !substream->ops->copy_user)
- memset(runtime->dma_area, 0, runtime->dma_bytes);
+ if (runtime->dma_area && !substream->ops->copy_user) {
+ size_t size;
+
+ if (runtime->dma_buffer_p)
+ size = runtime->dma_buffer_p->bytes;
+ else
+ size = runtime->dma_bytes;
+ memset(runtime->dma_area, 0, size);
+ }
snd_pcm_timer_resolution_change(substream);
snd_pcm_set_state(substream, SNDRV_PCM_STATE_SETUP);