[PATCH 03/12] PCI: Lock down BAR access when securelevel is enabled

Matthew Garrett
2013-09-09T15:52:15Z

Any hardware that can potentially generate DMA has to be locked down from
userspace in order to avoid it being possible for an attacker to modify
kernel code. This should be prevented if securelevel has been set. Default
to paranoid - in future we can potentially relax this for sufficiently
IOMMU-isolated devices.

Signed-off-by: Matthew Garrett <matthew.garrett@nebula.com>
---
drivers/pci/pci-sysfs.c | 9 +++++++++
drivers/pci/proc.c | 9 ++++++++-
drivers/pci/syscall.c | 3 ++-
3 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
index 7128cfd..0a3fca2 100644
--- a/drivers/pci/pci-sysfs.c
+++ b/drivers/pci/pci-sysfs.c
@@ -634,6 +634,9 @@ pci_write_config(struct file* filp, struct kobject *kobj,
loff_t init_off = off;
u8 *data = (u8*) buf;

+ if (get_securelevel() > 0)
+ return -EPERM;
+
if (off > dev->cfg_size)
return 0;
if (off + count > dev->cfg_size) {
@@ -940,6 +943,9 @@ pci_mmap_resource(struct kobject *kobj, struct bin_attribute *attr,
resource_size_t start, end;
int i;

+ if (get_securelevel() > 0)
+ return -EPERM;
+
for (i = 0; i < PCI_ROM_RESOURCE; i++)
if (res == &pdev->resource[i])
break;
@@ -1047,6 +1053,9 @@ pci_write_resource_io(struct file *filp, struct kobject *kobj,
struct bin_attribute *attr, char *buf,
loff_t off, size_t count)
{
+ if (get_securelevel() > 0)
+ return -EPERM;
+
return pci_resource_io(filp, kobj, attr, buf, off, count, true);
}

diff --git a/drivers/pci/proc.c b/drivers/pci/proc.c
index cdc7836..45c59e9 100644
--- a/drivers/pci/proc.c
+++ b/drivers/pci/proc.c
@@ -11,6 +11,7 @@
#include <linux/proc_fs.h>
#include <linux/seq_file.h>
#include <linux/capability.h>
+#include <linux/security.h>
#include <asm/uaccess.h>
#include <asm/byteorder.h>
#include "pci.h"
@@ -117,6 +118,9 @@ proc_bus_pci_write(struct file *file, const char __user *buf, size_t nbytes, lof
int size = dev->cfg_size;
int cnt;

+ if (get_securelevel() > 0)
+ return -EPERM;
+
if (pos >= size)
return 0;
if (nbytes >= size)
@@ -196,6 +200,9 @@ static long proc_bus_pci_ioctl(struct file *file, unsigned int cmd,
#endif /* HAVE_PCI_MMAP */
int ret = 0;

+ if (get_securelevel() > 0)
+ return -EPERM;
+
switch (cmd) {
case PCIIOC_CONTROLLER:
ret = pci_domain_nr(dev->bus);
@@ -234,7 +241,7 @@ static int proc_bus_pci_mmap(struct file *file, struct vm_area_struct *vma)
struct pci_filp_private *fpriv = file->private_data;
int i, ret;

- if (!capable(CAP_SYS_RAWIO))
+ if (!capable(CAP_SYS_RAWIO) || (get_securelevel() > 0))
return -EPERM;

/* Make sure the caller is mapping a real resource for this device */
diff --git a/drivers/pci/syscall.c b/drivers/pci/syscall.c
index e1c1ec5..d922577 100644
--- a/drivers/pci/syscall.c
+++ b/drivers/pci/syscall.c
@@ -10,6 +10,7 @@
#include <linux/errno.h>
#include <linux/pci.h>
#include <linux/syscalls.h>
+#include <linux/security.h>
#include <asm/uaccess.h>
#include "pci.h"

@@ -92,7 +93,7 @@ SYSCALL_DEFINE5(pciconfig_write, unsigned long, bus, unsigned long, dfn,
u32 dword;
int err = 0;

- if (!capable(CAP_SYS_ADMIN))
+ if (!capable(CAP_SYS_ADMIN) || (get_securelevel() > 0))
return -EPERM;

dev = pci_get_bus_and_slot(bus, dfn);
--
1.8.3.1