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From:   Alex Elder <elder@linaro.org>
To:     davem@davemloft.net, edumazet@google.com, kuba@kernel.org,
        pabeni@redhat.com
Cc:     quic_bjorande@quicinc.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
Subject: [PATCH net v2] net: ipa: compute DMA pool size properly
Date:   Tue, 28 Mar 2023 11:08:33 -0500
Message-Id: <20230328160833.2861095-1-elder@linaro.org>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

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: Bjorn Andersson <quic_bjorande@quicinc.com>
Tested-by: Bjorn Andersson <quic_bjorande@quicinc.com>
Fixes: 9dd441e4ed57 ("soc: qcom: ipa: GSI transactions")
Signed-off-by: Alex Elder <elder@linaro.org>
---
Note: This was reported via private communication.
v2: - Added Bjorn's actual name to tags.  

 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