linux-kernel - Re: [PATCH net] net: ipa: compute DMA pool size properly

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Message-Id: <2E9EE299-E500-429E-9D19-CA8A55326100@linaro.org>
Date:   Mon, 27 Mar 2023 18:40:49 -0500
From:   Alex Elder <alex.elder@...aro.org>
To:     Bjorn Andersson <quic_bjorande@...cinc.com>
Cc:     Alex Elder <elder@...aro.org>, davem@...emloft.net,
        edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com,
        caleb.connolly@...aro.org, mka@...omium.org, evgreen@...omium.org,
        andersson@...nel.org, quic_cpratapa@...cinc.com,
        quic_avuyyuru@...cinc.com, quic_jponduru@...cinc.com,
        quic_subashab@...cinc.com, elder@...nel.org,
        netdev@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net] net: ipa: compute DMA pool size properly



> On Mar 27, 2023, at 4:16 PM, Bjorn Andersson <quic_bjorande@...cinc.com> wrote:
> 
> On Sun, Mar 26, 2023 at 11:52:23AM -0500, Alex Elder wrote:
>> In gsi_trans_pool_init_dma(), the total size of a pool of memory
>> used for DMA transactions is calculated.  However the calculation is
>> done incorrectly.
>> 
>> For 4KB pages, this total size is currently always more than one
>> page, and as a result, the calculation produces a positive (though
>> incorrect) total size.  The code still works in this case; we just
>> end up with fewer DMA pool entries than we intended.
>> 
>> Bjorn Andersson tested booting a kernel with 16KB pages, and hit a
>> null pointer derereference in sg_alloc_append_table_from_pages(),
>> descending from gsi_trans_pool_init_dma().  The cause of this was
>> that a 16KB total size was going to be allocated, and with 16KB
>> pages the order of that allocation is 0.  The total_size calculation
>> yielded 0, which eventually led to the crash.
>> 
>> Correcting the total_size calculation fixes the problem.
>> 
>> Reported-by: <quic_bjorande@...cinc.com>
>> Tested-by: <quic_bjorande@...cinc.com>
> 
> It would be nice to add "Bjorn Andersson" to these two.
> 

Oh yeah sorry about that. I’ll add it.   -Alex

> Regards,
> Bjorn
> 
>> Fixes: 9dd441e4ed57 ("soc: qcom: ipa: GSI transactions")
>> Signed-off-by: Alex Elder <elder@...aro.org>
>> ---
>> drivers/net/ipa/gsi_trans.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>> 
>> diff --git a/drivers/net/ipa/gsi_trans.c b/drivers/net/ipa/gsi_trans.c
>> index 0f52c068c46d6..ee6fb00b71eb6 100644
>> --- a/drivers/net/ipa/gsi_trans.c
>> +++ b/drivers/net/ipa/gsi_trans.c
>> @@ -156,7 +156,7 @@ int gsi_trans_pool_init_dma(struct device *dev, struct gsi_trans_pool *pool,
>>     * gsi_trans_pool_exit_dma() can assume the total allocated
>>     * size is exactly (count * size).
>>     */
>> -    total_size = get_order(total_size) << PAGE_SHIFT;
>> +    total_size = PAGE_SIZE << get_order(total_size);
>> 
>>    virt = dma_alloc_coherent(dev, total_size, &addr, GFP_KERNEL);
>>    if (!virt)
>> -- 
>> 2.34.1
>>