linux-kernel - [RFC/PATCH 5/5] soc: qcom: cmd-db: Map with read-only mappings

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Message-Id: <20190517164746.110786-6-swboyd@chromium.org>
Date:   Fri, 17 May 2019 09:47:46 -0700
From:   Stephen Boyd <swboyd@...omium.org>
To:     linux-kernel@...r.kernel.org
Cc:     linux-arm-msm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
        Evan Green <evgreen@...omium.org>,
        Rob Herring <robh+dt@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Andy Gross <agross@...nel.org>,
        Will Deacon <will.deacon@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Dan Williams <dan.j.williams@...el.com>
Subject: [RFC/PATCH 5/5] soc: qcom: cmd-db: Map with read-only mappings

The command DB is read-only already to the kernel because everything is
const marked once we map it. Let's go one step further and try to map
the memory as read-only in the page tables. This should make it harder
for random code to corrupt the database and change the contents.

Cc: Evan Green <evgreen@...omium.org>
Cc: Rob Herring <robh+dt@...nel.org>
Cc: Bjorn Andersson <bjorn.andersson@...aro.org>
Cc: Andy Gross <agross@...nel.org>
Cc: Will Deacon <will.deacon@....com>
Cc: Catalin Marinas <catalin.marinas@....com>
Cc: Dan Williams <dan.j.williams@...el.com>
Signed-off-by: Stephen Boyd <swboyd@...omium.org>
---
 drivers/soc/qcom/cmd-db.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/soc/qcom/cmd-db.c b/drivers/soc/qcom/cmd-db.c
index 10a34d26b753..6365e8260282 100644
--- a/drivers/soc/qcom/cmd-db.c
+++ b/drivers/soc/qcom/cmd-db.c
@@ -240,7 +240,8 @@ static int cmd_db_dev_probe(struct platform_device *pdev)
 {
 	int ret = 0;
 
-	cmd_db_header = devm_memremap_reserved_mem(&pdev->dev, MEMREMAP_WB);
+	cmd_db_header = devm_memremap_reserved_mem(&pdev->dev,
+						   MEMREMAP_RO | MEMREMAP_WB);
 	if (IS_ERR(cmd_db_header)) {
 		ret = PTR_ERR(cmd_db_header);
 		cmd_db_header = NULL;
-- 
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