linux-kernel - [PATCH v4 8/8] bus: mhi: core: Ensure non-zero session or sequence ID values are used

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Message-Id: <1588386725-1165-9-git-send-email-bbhatt@codeaurora.org>
Date:   Fri,  1 May 2020 19:32:05 -0700
From:   Bhaumik Bhatt <bbhatt@...eaurora.org>
To:     mani@...nel.org
Cc:     linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        hemantk@...eaurora.org, jhugo@...eaurora.org,
        Bhaumik Bhatt <bbhatt@...eaurora.org>
Subject: [PATCH v4 8/8] bus: mhi: core: Ensure non-zero session or sequence ID values are used

While writing any sequence or session identifiers, it is possible that
the host could write a zero value, whereas only non-zero values should
be supported writes to those registers. Ensure that the host does not
write a non-zero value for them and also log them in debug messages.

Suggested-by: Jeffrey Hugo <jhugo@...eaurora.org>
Signed-off-by: Bhaumik Bhatt <bbhatt@...eaurora.org>
---
 drivers/bus/mhi/core/boot.c     | 15 +++++++--------
 drivers/bus/mhi/core/internal.h |  1 +
 2 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/drivers/bus/mhi/core/boot.c b/drivers/bus/mhi/core/boot.c
index e5fcde1..9fe9c59 100644
--- a/drivers/bus/mhi/core/boot.c
+++ b/drivers/bus/mhi/core/boot.c
@@ -43,10 +43,7 @@ void mhi_rddm_prepare(struct mhi_controller *mhi_cntrl,
 		      lower_32_bits(mhi_buf->dma_addr));
 
 	mhi_write_reg(mhi_cntrl, base, BHIE_RXVECSIZE_OFFS, mhi_buf->len);
-	sequence_id = prandom_u32() & BHIE_RXVECSTATUS_SEQNUM_BMSK;
-
-	if (unlikely(!sequence_id))
-		sequence_id = 1;
+	sequence_id = (MHI_RANDOM_U32_NONZERO & BHIE_RXVECSTATUS_SEQNUM_BMSK);
 
 	mhi_write_reg_field(mhi_cntrl, base, BHIE_RXVECDB_OFFS,
 			    BHIE_RXVECDB_SEQNUM_BMSK, BHIE_RXVECDB_SEQNUM_SHFT,
@@ -189,7 +186,9 @@ static int mhi_fw_load_amss(struct mhi_controller *mhi_cntrl,
 		return -EIO;
 	}
 
-	dev_dbg(dev, "Starting AMSS download via BHIe\n");
+	sequence_id = (MHI_RANDOM_U32_NONZERO & BHIE_TXVECSTATUS_SEQNUM_BMSK);
+	dev_dbg(dev, "Starting AMSS download via BHIe. Sequence ID:%u\n",
+		sequence_id);
 	mhi_write_reg(mhi_cntrl, base, BHIE_TXVECADDR_HIGH_OFFS,
 		      upper_32_bits(mhi_buf->dma_addr));
 
@@ -198,7 +197,6 @@ static int mhi_fw_load_amss(struct mhi_controller *mhi_cntrl,
 
 	mhi_write_reg(mhi_cntrl, base, BHIE_TXVECSIZE_OFFS, mhi_buf->len);
 
-	sequence_id = prandom_u32() & BHIE_TXVECSTATUS_SEQNUM_BMSK;
 	mhi_write_reg_field(mhi_cntrl, base, BHIE_TXVECDB_OFFS,
 			    BHIE_TXVECDB_SEQNUM_BMSK, BHIE_TXVECDB_SEQNUM_SHFT,
 			    sequence_id);
@@ -246,14 +244,15 @@ static int mhi_fw_load_sbl(struct mhi_controller *mhi_cntrl,
 		goto invalid_pm_state;
 	}
 
-	dev_dbg(dev, "Starting SBL download via BHI\n");
+	session_id = (MHI_RANDOM_U32_NONZERO & BHI_TXDB_SEQNUM_BMSK);
+	dev_dbg(dev, "Starting SBL download via BHI. Session ID:%u\n",
+		session_id);
 	mhi_write_reg(mhi_cntrl, base, BHI_STATUS, 0);
 	mhi_write_reg(mhi_cntrl, base, BHI_IMGADDR_HIGH,
 		      upper_32_bits(dma_addr));
 	mhi_write_reg(mhi_cntrl, base, BHI_IMGADDR_LOW,
 		      lower_32_bits(dma_addr));
 	mhi_write_reg(mhi_cntrl, base, BHI_IMGSIZE, size);
-	session_id = prandom_u32() & BHI_TXDB_SEQNUM_BMSK;
 	mhi_write_reg(mhi_cntrl, base, BHI_IMGTXDB, session_id);
 	read_unlock_bh(pm_lock);
 
diff --git a/drivers/bus/mhi/core/internal.h b/drivers/bus/mhi/core/internal.h
index 0965ca3..e4e6ea2 100644
--- a/drivers/bus/mhi/core/internal.h
+++ b/drivers/bus/mhi/core/internal.h
@@ -452,6 +452,7 @@ enum mhi_pm_state {
 #define PRIMARY_CMD_RING		0
 #define MHI_DEV_WAKE_DB			127
 #define MHI_MAX_MTU			0xffff
+#define MHI_RANDOM_U32_NONZERO		(prandom_u32_max(U32_MAX - 1) + 1)
 
 enum mhi_er_type {
 	MHI_ER_TYPE_INVALID = 0x0,
-- 
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