linux-kernel - [RESEND PATCH 5/6] crypto: caam: add logic to detect when running under TrustZone

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Message-Id: <1516805435-15034-6-git-send-email-pure.logic@nexus-software.ie>
Date:   Wed, 24 Jan 2018 14:50:34 +0000
From:   Bryan O'Donoghue <pure.logic@...us-software.ie>
To:     horia.geanta@....com, aymen.sghaier@....com,
        linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     fabio.estevam@....com, peng.fan@....com,
        herbert@...dor.apana.org.au, davem@...emloft.net,
        lukas.auer@...ec.fraunhofer.de, rui.silva@...aro.org,
        ryan.harkin@...aro.org,
        Bryan O'Donoghue <pure.logic@...us-software.ie>
Subject: [RESEND PATCH 5/6] crypto: caam: add logic to detect when running under TrustZone

This patch introduces logic to ascertain if the CAAM is running in
TrustZone mode or not. When running in TrustZone mode the first page of the
CAAM will read-back all zero for each register. This means for a register
such as the MCR - if we detect an all zero register - we can run a simple
test to try to toggle a bit inside of that register.

If the MCR is non-zero we already know we are in a non TrustZone mode.

If we read zero in the MCR but can successfully toggle a bit inside of the
MCR we know we are in a non TrustZone mode. So we set the bit back to zero
and continue.

If we read zero and cannot toggle a bit in the MCR we have successfully
detected TrustZone mode.

Once TrustZone is active the range of functions we can perform on CAAM is
limited; however the CAAM is still usable provided a previous stage in the
boot process initialized the block correctly.

Separate patches will handle the case of determining if the block is usable
when ctrlpriv->trustzone is true.

Signed-off-by: Bryan O'Donoghue <pure.logic@...us-software.ie>
Cc: "Horia Geantă" <horia.geanta@....com>
Cc: Aymen Sghaier <aymen.sghaier@....com>
Cc: Fabio Estevam <fabio.estevam@....com>
Cc: Peng Fan <peng.fan@....com>
Cc: Herbert Xu <herbert@...dor.apana.org.au>
Cc: "David S. Miller" <davem@...emloft.net>
Cc: Lukas Auer <lukas.auer@...ec.fraunhofer.de>
---
 drivers/crypto/caam/ctrl.c   | 21 +++++++++++++++++++++
 drivers/crypto/caam/intern.h |  1 +
 2 files changed, 22 insertions(+)

diff --git a/drivers/crypto/caam/ctrl.c b/drivers/crypto/caam/ctrl.c
index 0a1e96b..7fd3bfc 100644
--- a/drivers/crypto/caam/ctrl.c
+++ b/drivers/crypto/caam/ctrl.c
@@ -571,6 +571,27 @@ static int caam_probe(struct platform_device *pdev)
 			       MCFGR_LONG_PTR : 0));
 
 	/*
+	 * Detect if we are in TrustZone mode by trying to set MCFGR_LARGE_BURST
+	 * In the first instance if TrustZone is active the MCR will read
+	 * all-zero so if we read non-zero we know we can skip further checks.
+	 * However its possible MCR is zero in non-TrustZone mode so if
+	 * ctrl->mcr == 0 try to flip MCFGR_LARGE_BURST. If we cannot set the
+	 * bit when MCR is zero we've detected TrustZone mode and then we know
+	 * the first page of the CAAM is not accessible to Linux else flip
+	 * MCFGR_LARGE_BURST back to off.
+	 */
+	if (!rd_reg32(&ctrl->mcr)) {
+		clrsetbits_32(&ctrl->mcr, 0, MCFGR_LARGE_BURST);
+		if (!rd_reg32(&ctrl->mcr))
+			ctrlpriv->trust_zone = true;
+		else
+			clrsetbits_32(&ctrl->mcr, MCFGR_LARGE_BURST, 0);
+
+		if (ctrlpriv->trust_zone)
+			dev_info(dev, "TrustZone mode detected\n");
+	}
+
+	/*
 	 *  Read the Compile Time paramters and SCFGR to determine
 	 * if Virtualization is enabled for this platform
 	 */
diff --git a/drivers/crypto/caam/intern.h b/drivers/crypto/caam/intern.h
index 91f1107..6ff382b 100644
--- a/drivers/crypto/caam/intern.h
+++ b/drivers/crypto/caam/intern.h
@@ -84,6 +84,7 @@ struct caam_drv_private {
 	u8 qi_present;		/* Nonzero if QI present in device */
 	int secvio_irq;		/* Security violation interrupt number */
 	int virt_en;		/* Virtualization enabled in CAAM */
+	bool trust_zone;	/* TrustZone mode detected */
 
 #define	RNG4_MAX_HANDLES 2
 	/* RNG4 block */
-- 
2.7.4