linux-kernel - [PATCH] bus: mhi: ep: Update read pointer only after buffer is written

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Message-ID: <20250409-rp_fix-v1-1-8cf1fa22ed28@quicinc.com>
Date: Wed, 9 Apr 2025 16:17:43 +0530
From: Sumit Kumar <quic_sumk@...cinc.com>
To: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        Alex Elder
	<elder@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC: <mhi@...ts.linux.dev>, <linux-arm-msm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <quic_krichai@...cinc.com>,
        <quic_akhvin@...cinc.com>, <quic_skananth@...cinc.com>,
        <quic_vbadigan@...cinc.com>, <stable@...r.kernel.org>,
        Youssef Samir
	<quic_yabdulra@...cinc.com>,
        Sumit Kumar <quic_sumk@...cinc.com>
Subject: [PATCH] bus: mhi: ep: Update read pointer only after buffer is
 written

Inside mhi_ep_ring_add_element, the read pointer (rd_offset) is updated
before the buffer is written, potentially causing race conditions where
the host sees an updated read pointer before the buffer is actually
written. Updating rd_offset prematurely can lead to the host accessing
an uninitialized or incomplete element, resulting in data corruption.

Invoke the buffer write before updating rd_offset to ensure the element
is fully written before signaling its availability.

Fixes: bbdcba57a1a2 ("bus: mhi: ep: Add support for ring management")
cc: stable@...r.kernel.org
Co-developed-by: Youssef Samir <quic_yabdulra@...cinc.com>
Signed-off-by: Youssef Samir <quic_yabdulra@...cinc.com>
Signed-off-by: Sumit Kumar <quic_sumk@...cinc.com>
---
---
 drivers/bus/mhi/ep/ring.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/drivers/bus/mhi/ep/ring.c b/drivers/bus/mhi/ep/ring.c
index aeb53b2c34a8cd859393529d0c8860462bc687ed..26357ee68dee984d70ae5bf39f8f09f2cbcafe30 100644
--- a/drivers/bus/mhi/ep/ring.c
+++ b/drivers/bus/mhi/ep/ring.c
@@ -131,19 +131,23 @@ int mhi_ep_ring_add_element(struct mhi_ep_ring *ring, struct mhi_ring_element *e
 	}
 
 	old_offset = ring->rd_offset;
-	mhi_ep_ring_inc_index(ring);
 
 	dev_dbg(dev, "Adding an element to ring at offset (%zu)\n", ring->rd_offset);
+	buf_info.host_addr = ring->rbase + (old_offset * sizeof(*el));
+	buf_info.dev_addr = el;
+	buf_info.size = sizeof(*el);
+
+	ret = mhi_cntrl->write_sync(mhi_cntrl, &buf_info);
+	if (ret)
+		return ret;
+
+	mhi_ep_ring_inc_index(ring);
 
 	/* Update rp in ring context */
 	rp = cpu_to_le64(ring->rd_offset * sizeof(*el) + ring->rbase);
 	memcpy_toio((void __iomem *) &ring->ring_ctx->generic.rp, &rp, sizeof(u64));
 
-	buf_info.host_addr = ring->rbase + (old_offset * sizeof(*el));
-	buf_info.dev_addr = el;
-	buf_info.size = sizeof(*el);
-
-	return mhi_cntrl->write_sync(mhi_cntrl, &buf_info);
+	return ret;
 }
 
 void mhi_ep_ring_init(struct mhi_ep_ring *ring, enum mhi_ep_ring_type type, u32 id)

---
base-commit: 1e26c5e28ca5821a824e90dd359556f5e9e7b89f
change-id: 20250328-rp_fix-d7ebc18bc3be

Best regards,
-- 
Sumit Kumar <quic_sumk@...cinc.com>