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

Francesco Dolcini
2022-01-28T08:29:26Z

From: Jason Liu <jason.hui.liu@nxp.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@nxp.com>
Reviewed-by: Richard Zhu <hongxing.zhu@nxp.com>
Signed-off-by: Francesco Dolcini <francesco.dolcini@toradex.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