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[209.85.208.181]) by smtp.gmail.com with ESMTPSA id e29sm1177199ljb.105.2019.09.18.12.41.28 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 18 Sep 2019 12:41:29 -0700 (PDT) Received: by mail-lj1-f181.google.com with SMTP id s19so1132116lji.6 for ; Wed, 18 Sep 2019 12:41:28 -0700 (PDT) X-Received: by 2002:a2e:9881:: with SMTP id b1mr3145788ljj.134.1568835688462; Wed, 18 Sep 2019 12:41:28 -0700 (PDT) MIME-Version: 1.0 References: <20190910160903.65694-1-swboyd@chromium.org> <20190910160903.65694-6-swboyd@chromium.org> In-Reply-To: <20190910160903.65694-6-swboyd@chromium.org> From: Evan Green Date: Wed, 18 Sep 2019 12:40:52 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH v3 5/5] soc: qcom: cmd-db: Map with read-only mappings To: Stephen Boyd Cc: Dan Williams , LKML , linux-arm-msm , linux-arm Mailing List , "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" , Rob Herring , Bjorn Andersson , Andy Gross , Will Deacon , Catalin Marinas Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Sep 10, 2019 at 9:09 AM Stephen Boyd wrote: > > 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 > Cc: Rob Herring > Cc: Bjorn Andersson > Cc: Andy Gross > Cc: Will Deacon > Cc: Catalin Marinas > Cc: Dan Williams > Reviewed-by: Bjorn Andersson > Signed-off-by: Stephen Boyd > --- > 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); It seems weird to have both flags, like: "It's read-only, but if it ever did get written to somehow, make it writeback". > if (IS_ERR(cmd_db_header)) { > ret = PTR_ERR(cmd_db_header); > cmd_db_header = NULL; > -- > Sent by a computer through tubes >