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From:   Alex Elder <alex.elder@linaro.org>
Mime-Version: 1.0 (1.0)
Subject: Re: [PATCH net] net: ipa: compute DMA pool size properly
Date:   Mon, 27 Mar 2023 18:40:49 -0500
Message-Id: <2E9EE299-E500-429E-9D19-CA8A55326100@linaro.org>
References: <20230327211627.GA3248042@hu-bjorande-lv.qualcomm.com>
Cc:     Alex Elder <elder@linaro.org>, davem@davemloft.net,
        edumazet@google.com, kuba@kernel.org, pabeni@redhat.com,
        caleb.connolly@linaro.org, mka@chromium.org, evgreen@chromium.org,
        andersson@kernel.org, quic_cpratapa@quicinc.com,
        quic_avuyyuru@quicinc.com, quic_jponduru@quicinc.com,
        quic_subashab@quicinc.com, elder@kernel.org,
        netdev@vger.kernel.org, linux-arm-msm@vger.kernel.org,
        linux-kernel@vger.kernel.org
In-Reply-To: <20230327211627.GA3248042@hu-bjorande-lv.qualcomm.com>
To:     Bjorn Andersson <quic_bjorande@quicinc.com>
Precedence: bulk


> On Mar 27, 2023, at 4:16 PM, Bjorn Andersson <quic_bjorande@quicinc.com> w=
rote:
>=20
> =EF=BB=BFOn 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.
>>=20
>> 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.
>>=20
>> 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.
>>=20
>> Correcting the total_size calculation fixes the problem.
>>=20
>> Reported-by: <quic_bjorande@quicinc.com>
>> Tested-by: <quic_bjorande@quicinc.com>
>=20
> It would be nice to add "Bjorn Andersson" to these two.
>=20

Oh yeah sorry about that. I=E2=80=99ll add it.   -Alex

> Regards,
> Bjorn
>=20
>> Fixes: 9dd441e4ed57 ("soc: qcom: ipa: GSI transactions")
>> Signed-off-by: Alex Elder <elder@linaro.org>
>> ---
>> drivers/net/ipa/gsi_trans.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>=20
>> 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, struc=
t gsi_trans_pool *pool,
>>     * gsi_trans_pool_exit_dma() can assume the total allocated
>>     * size is exactly (count * size).
>>     */
>> -    total_size =3D get_order(total_size) << PAGE_SHIFT;
>> +    total_size =3D PAGE_SIZE << get_order(total_size);
>>=20
>>    virt =3D dma_alloc_coherent(dev, total_size, &addr, GFP_KERNEL);
>>    if (!virt)
>> --=20
>> 2.34.1
>>=20