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@vger.kernel.org
Co-developed-by: Youssef Samir <quic_yabdulra@quicinc.com>
Signed-off-by: Youssef Samir <quic_yabdulra@quicinc.com>
Signed-off-by: Sumit Kumar <quic_sumk@quicinc.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@quicinc.com>

On Wed, Apr 09, 2025 at 04:17:43PM +0530, Sumit Kumar wrote:
> 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@vger.kernel.org
> Co-developed-by: Youssef Samir <quic_yabdulra@quicinc.com>
> Signed-off-by: Youssef Samir <quic_yabdulra@quicinc.com>
> Signed-off-by: Sumit Kumar <quic_sumk@quicinc.com>

Applied to mhi-fixes!

- Mani

> ---
> ---
>  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@quicinc.com>
> 

-- 
மணிவண்ணன் சதாசிவம்

On Wed, Apr 09, 2025 at 04:17:43PM +0530, Sumit Kumar wrote:
> 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.
> 

Hmm. I was under assumption that the host wouldn't access the rd_offset before
raising the interrupt.

But anyway, the fix looks legitimate irrespective of that.

> Fixes: bbdcba57a1a2 ("bus: mhi: ep: Add support for ring management")
> cc: stable@vger.kernel.org
> Co-developed-by: Youssef Samir <quic_yabdulra@quicinc.com>
> Signed-off-by: Youssef Samir <quic_yabdulra@quicinc.com>
> Signed-off-by: Sumit Kumar <quic_sumk@quicinc.com>

Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>

- Mani

> ---
> ---
>  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@quicinc.com>
> 

-- 
மணிவண்ணன் சதாசிவம்

On 4/9/2025 4:47 AM, Sumit Kumar wrote:
> 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@vger.kernel.org
> Co-developed-by: Youssef Samir <quic_yabdulra@quicinc.com>
> Signed-off-by: Youssef Samir <quic_yabdulra@quicinc.com>
> Signed-off-by: Sumit Kumar <quic_sumk@quicinc.com>

Reviewed-by: Jeff Hugo <jeff.hugo@oss.qualcomm.com>

On 4/9/2025 4:17 PM, Sumit Kumar wrote:
> 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@vger.kernel.org
> Co-developed-by: Youssef Samir <quic_yabdulra@quicinc.com>
> Signed-off-by: Youssef Samir <quic_yabdulra@quicinc.com>
> Signed-off-by: Sumit Kumar <quic_sumk@quicinc.com>
Reviewed-by: Krishna Chaitanya Chundru <krishna.chundru@oss.qualcomm.com>

- Krishna Chaitanya.
> ---
> ---
>   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,