PCI/switchtec: Add Gen4 MRPC GAS access permission check

Gen4 hardware provides new MRPC commands to read and write directly from
any address in the PCI BAR (which Microsemi refers to as GAS). Since
accessing BARs can be dangerous and break the driver, we don't want
unprivileged users to have this ability.

Therefore, require CAP_SYS_ADMIN for the local and remote GAS access MRPC
commands. Privileged processes will already have access to the BAR through
the sysfs resource file so this doesn't give userspace any capabilities it
didn't already have.

[logang@deltatee.com: rework commit message]
Link: https://lore.kernel.org/r/20200106190337.2428-11-logang@deltatee.com
Signed-off-by: Kelvin Cao <kelvin.cao@microchip.com>
Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

diff --git a/drivers/pci/switch/switchtec.c b/drivers/pci/switch/switchtec.c
index af85d232d200b39eb10f3274544bf34392874ced..92b95e8067c0cddb19bc55f7cf75a2f1d38050b1 100644 (file)
--- a/drivers/pci/switch/switchtec.c
+++ b/drivers/pci/switch/switchtec.c
@@ -479,6 +479,12 @@ static ssize_t switchtec_dev_write(struct file *filp, const char __user *data,
                rc = -EFAULT;
                goto out;
        }
+       if (((MRPC_CMD_ID(stuser->cmd) == MRPC_GAS_WRITE) ||
+            (MRPC_CMD_ID(stuser->cmd) == MRPC_GAS_READ)) &&
+           !capable(CAP_SYS_ADMIN)) {
+               rc = -EPERM;
+               goto out;
+       }
 
        data += sizeof(stuser->cmd);
        rc = copy_from_user(&stuser->data, data, size - sizeof(stuser->cmd));

diff --git a/include/linux/switchtec.h b/include/linux/switchtec.h
index e8515524413581dbce2ef00dd9e652568bcc1677..082f1d51957a4cd3c1d0660052c545a049e01775 100644 (file)
--- a/include/linux/switchtec.h
+++ b/include/linux/switchtec.h
@@ -21,6 +21,11 @@
 #define SWITCHTEC_EVENT_FATAL    BIT(4)
 
 #define SWITCHTEC_DMA_MRPC_EN  BIT(0)
+
+#define MRPC_GAS_READ          0x29
+#define MRPC_GAS_WRITE         0x87
+#define MRPC_CMD_ID(x)         ((x) & 0xffff)
+
 enum {
        SWITCHTEC_GAS_MRPC_OFFSET       = 0x0000,
        SWITCHTEC_GAS_TOP_CFG_OFFSET    = 0x1000,