linux-kernel - [PATCH 03/12] PCI: Lock down BAR access when trusted

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Message-Id: <1393445473-15068-4-git-send-email-matthew.garrett@nebula.com>
Date:	Wed, 26 Feb 2014 15:11:04 -0500
From:	Matthew Garrett <matthew.garrett@...ula.com>
To:	linux-kernel@...r.kernel.org
Cc:	keescook@...omium.org, gregkh@...uxfoundation.org, hpa@...or.com,
	linux-efi@...r.kernel.org, jmorris@...ei.org,
	linux-security-module@...r.kernel.org,
	Matthew Garrett <matthew.garrett@...ula.com>
Subject: [PATCH 03/12] PCI: Lock down BAR access when trusted_kernel is true

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 trusted_kernel 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@...ula.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 276ef9c..256f373 100644
--- a/drivers/pci/pci-sysfs.c
+++ b/drivers/pci/pci-sysfs.c
@@ -663,6 +663,9 @@ pci_write_config(struct file* filp, struct kobject *kobj,
 	loff_t init_off = off;
 	u8 *data = (u8*) buf;
 
+	if (get_trusted_kernel())
+		return -EPERM;
+
 	if (off > dev->cfg_size)
 		return 0;
 	if (off + count > dev->cfg_size) {
@@ -969,6 +972,9 @@ pci_mmap_resource(struct kobject *kobj, struct bin_attribute *attr,
 	resource_size_t start, end;
 	int i;
 
+	if (get_trusted_kernel())
+		return -EPERM;
+
 	for (i = 0; i < PCI_ROM_RESOURCE; i++)
 		if (res == &pdev->resource[i])
 			break;
@@ -1076,6 +1082,9 @@ pci_write_resource_io(struct file *filp, struct kobject *kobj,
 		      struct bin_attribute *attr, char *buf,
 		      loff_t off, size_t count)
 {
+	if (get_trusted_kernel())
+		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 46d1378..990b24b 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_trusted_kernel())
+		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_trusted_kernel())
+		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_trusted_kernel()))
 		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 24750a1..d962710 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_trusted_kernel()))
 		return -EPERM;
 
 	dev = pci_get_bus_and_slot(bus, dfn);
-- 
1.8.5.3

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