linux-kernel - [RFC PATCH] PCI: imx6: Handle the abort from user-space

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Date:   Fri, 28 Jan 2022 09:29:20 +0100
From:   Francesco Dolcini <francesco.dolcini@...adex.com>
To:     Richard Zhu <hongxing.zhu@....com>,
        Lucas Stach <l.stach@...gutronix.de>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Rob Herring <robh@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        NXP Linux Team <linux-imx@....com>,
        Jason Liu <jason.hui.liu@....com>
Cc:     linux-pci@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, Bjorn Helgaas <bhelgaas@...gle.com>,
        Shawn Guo <shawnguo@...nel.org>,
        Francesco Dolcini <francesco.dolcini@...adex.com>
Subject: [RFC PATCH] PCI: imx6: Handle the abort from user-space

From: Jason Liu <jason.hui.liu@....com>

The driver install one hook to handle the external abort, but issue
is that if the abort introduced from user space code, the following
code unsigned long instr = *(unsigned long *)pc; which will created
another data-abort(page domain fault) if CONFIG_CPU_SW_DOMAIN_PAN.

The patch does not intent to use copy_from_user and then do the hack
due to the security consideration. In fact, we can just return and
report the external abort to user-space.

Signed-off-by: Jason Liu <jason.hui.liu@....com>
Reviewed-by: Richard Zhu <hongxing.zhu@....com>
Signed-off-by: Francesco Dolcini <francesco.dolcini@...adex.com>
---
We have this patch from NXP downstream kernel [1] in our kernel branch [2]
since a long time, to me it would make sense to upstream it. Any concern?

[1] https://source.codeaurora.org/external/imxsupport/linux-imx/commit/?id=62dfb2fb953463dd1b6710567c9e174672a98f24
[2] https://git.toradex.com/cgit/linux-toradex.git/commit/?id=2b42547cf659f979be2defdff6a99f921b33d0f1
---
 drivers/pci/controller/dwc/pci-imx6.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/drivers/pci/controller/dwc/pci-imx6.c b/drivers/pci/controller/dwc/pci-imx6.c
index 6974bd5aa116..6b178a29e253 100644
--- a/drivers/pci/controller/dwc/pci-imx6.c
+++ b/drivers/pci/controller/dwc/pci-imx6.c
@@ -27,6 +27,7 @@
 #include <linux/resource.h>
 #include <linux/signal.h>
 #include <linux/types.h>
+#include <linux/uaccess.h>
 #include <linux/interrupt.h>
 #include <linux/reset.h>
 #include <linux/phy/phy.h>
@@ -297,8 +298,15 @@ static int imx6q_pcie_abort_handler(unsigned long addr,
 		unsigned int fsr, struct pt_regs *regs)
 {
 	unsigned long pc = instruction_pointer(regs);
-	unsigned long instr = *(unsigned long *)pc;
-	int reg = (instr >> 12) & 15;
+	unsigned long instr;
+	int reg;
+
+	/* if the abort from user-space, just return and report it */
+	if (user_mode(regs))
+		return 1;
+
+	instr = *(unsigned long *)pc;
+	reg = (instr >> 12) & 15;
 
 	/*
 	 * If the instruction being executed was a read,
-- 
2.25.1