linux-kernel - Re: [PATCH V3 02/11] PCI: Lock down BAR access when module security is enabled

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Date:	Wed, 4 Sep 2013 10:45:37 +1000 (EST)
From:	James Morris <jmorris@...ei.org>
To:	Matthew Garrett <matthew.garrett@...ula.com>
cc:	linux-kernel@...r.kernel.org, linux-efi@...r.kernel.org,
	keescook@...omium.org, hpa@...or.com
Subject: Re: [PATCH V3 02/11] PCI: Lock down BAR access when module security
 is enabled

On Tue, 3 Sep 2013, Matthew Garrett wrote:

> 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, allowing them to circumvent disabled module loading or module
> signing. Default to paranoid - in future we can potentially relax this for
> sufficiently IOMMU-isolated devices.
> 
> Signed-off-by: Matthew Garrett <matthew.garrett@...ula.com>


Reviewed-by: James Morris <jmorris@...ei.org>



> ---
>  drivers/pci/pci-sysfs.c | 10 ++++++++++
>  drivers/pci/proc.c      |  8 +++++++-
>  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 c0dbe1f..cd4e35f 100644
> --- a/drivers/pci/pci-sysfs.c
> +++ b/drivers/pci/pci-sysfs.c
> @@ -29,6 +29,7 @@
>  #include <linux/slab.h>
>  #include <linux/vgaarb.h>
>  #include <linux/pm_runtime.h>
> +#include <linux/module.h>
>  #include "pci.h"
>  
>  static int sysfs_initialized;	/* = 0 */
> @@ -624,6 +625,9 @@ pci_write_config(struct file* filp, struct kobject *kobj,
>  	loff_t init_off = off;
>  	u8 *data = (u8*) buf;
>  
> +	if (secure_modules())
> +		return -EPERM;
> +
>  	if (off > dev->cfg_size)
>  		return 0;
>  	if (off + count > dev->cfg_size) {
> @@ -930,6 +934,9 @@ pci_mmap_resource(struct kobject *kobj, struct bin_attribute *attr,
>  	resource_size_t start, end;
>  	int i;
>  
> +	if (secure_modules())
> +		return -EPERM;
> +
>  	for (i = 0; i < PCI_ROM_RESOURCE; i++)
>  		if (res == &pdev->resource[i])
>  			break;
> @@ -1037,6 +1044,9 @@ pci_write_resource_io(struct file *filp, struct kobject *kobj,
>  		      struct bin_attribute *attr, char *buf,
>  		      loff_t off, size_t count)
>  {
> +	if (secure_modules())
> +		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..e3d498b 100644
> --- a/drivers/pci/proc.c
> +++ b/drivers/pci/proc.c
> @@ -117,6 +117,9 @@ proc_bus_pci_write(struct file *file, const char __user *buf, size_t nbytes, lof
>  	int size = dev->cfg_size;
>  	int cnt;
>  
> +	if (secure_modules())
> +		return -EPERM;
> +
>  	if (pos >= size)
>  		return 0;
>  	if (nbytes >= size)
> @@ -196,6 +199,9 @@ static long proc_bus_pci_ioctl(struct file *file, unsigned int cmd,
>  #endif /* HAVE_PCI_MMAP */
>  	int ret = 0;
>  
> +	if (secure_modules())
> +		return -EPERM;
> +
>  	switch (cmd) {
>  	case PCIIOC_CONTROLLER:
>  		ret = pci_domain_nr(dev->bus);
> @@ -234,7 +240,7 @@ 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) || secure_modules())
>  		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..bffbf71 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/module.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) || secure_modules())
>  		return -EPERM;
>  
>  	dev = pci_get_bus_and_slot(bus, dfn);
> -- 
> 1.8.3.1
> 
> --
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-- 
James Morris
<jmorris@...ei.org>
--
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