Re: [PATCH v3] dma-buf: dma-heap: Add a size check for allocation

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Am 13.01.22 um 14:00 schrieb Ruhl, Michael J:
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Subject: RE: [PATCH v3] dma-buf: dma-heap: Add a size check for allocation


-----Original Message-----
From: dri-devel <dri-devel-bounces@xxxxxxxxxxxxxxxxxxxxx> On Behalf Of
guangming.cao@xxxxxxxxxxxx
Sent: Thursday, January 13, 2022 7:34 AM
To: sumit.semwal@xxxxxxxxxx
Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; mingyuan.ma@xxxxxxxxxxxx;
Guangming <Guangming.Cao@xxxxxxxxxxxx>;
wsd_upstream@xxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; dri-
devel@xxxxxxxxxxxxxxxxxxxxx; linaro-mm-sig@xxxxxxxxxxxxxxxx;
yf.wang@xxxxxxxxxxxx; libo.kang@xxxxxxxxxxxx;
benjamin.gaignard@xxxxxxxxxx; bo.song@xxxxxxxxxxxx;
matthias.bgg@xxxxxxxxx; linux-mediatek@xxxxxxxxxxxxxxxxxxx;
lmark@xxxxxxxxxxxxxx; labbott@xxxxxxxxxx; christian.koenig@xxxxxxx;
jianjiao.zeng@xxxxxxxxxxxx; linux-media@xxxxxxxxxxxxxxx
Subject: [PATCH v3] dma-buf: dma-heap: Add a size check for allocation

From: Guangming <Guangming.Cao@xxxxxxxxxxxx>

Add a size check for allocation since the allocation size is
always less than the total DRAM size.

Without this check, once the invalid size allocation runs on a process that
can't be killed by OOM flow(such as "gralloc" on Android devices), it will
cause a kernel exception, and to make matters worse, we can't find who are
using
so many memory with "dma_buf_debug_show" since the relevant dma-buf
hasn't exported.

To make OOM issue easier, maybe need dma-buf framework to dump the
buffer size
under allocating in "dma_buf_debug_show".

Signed-off-by: Guangming <Guangming.Cao@xxxxxxxxxxxx>
Signed-off-by: jianjiao zeng <jianjiao.zeng@xxxxxxxxxxxx>
---
v3: 1. update patch, use right shift to replace division.
    2. update patch, add reason in code and commit message.
v2: 1. update size limitation as total_dram page size.
    2. update commit message
---
drivers/dma-buf/dma-heap.c | 10 ++++++++++
1 file changed, 10 insertions(+)

diff --git a/drivers/dma-buf/dma-heap.c b/drivers/dma-buf/dma-heap.c
index 56bf5ad01ad5..1fd382712584 100644
--- a/drivers/dma-buf/dma-heap.c
+++ b/drivers/dma-buf/dma-heap.c
@@ -55,6 +55,16 @@ static int dma_heap_buffer_alloc(struct dma_heap
*heap, size_t len,
	struct dma_buf *dmabuf;
	int fd;

+	/*
+	 * Invalid size check. The "len" should be less than totalram.
+	 *
+	 * Without this check, once the invalid size allocation runs on a process
that
+	 * can't be killed by OOM flow(such as "gralloc" on Android devices), it
will
+	 * cause a kernel exception, and to make matters worse, we can't find
who are using
+	 * so many memory with "dma_buf_debug_show" since the relevant
dma-buf hasn't exported.
+	 */
+	if (len >> PAGE_SHIFT > totalram_pages())
If your "heap" is from cma, is this still a valid check?
And thinking a bit further, if I create a heap from something else (say device memory),
you will need to be able to figure out the maximum allowable check for the specific
heap.

Maybe the heap needs a callback for max size?

Well we currently maintain a separate allocator and don't use dma-heap, but yes we have systems with 16GiB device and only 8GiB system memory so that check here is certainly not correct.

In general I would rather let the system run into -ENOMEM or -EINVAL from the allocator instead.

Regards,
Christian.


m
M

+		return -EINVAL;
	/*
	 * Allocations from all heaps have to begin
	 * and end on page boundaries.
--
2.17.1




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