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SubjectRe: [PATCH 12/24] PCI: Lock down BAR access when the kernel is locked down
On Wed, Apr 05, 2017 at 09:16:18PM +0100, David Howells wrote:
> From: Matthew Garrett <matthew.garrett@nebula.com>
>
> Any hardware that can potentially generate DMA has to be locked down 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@nebula.com>
> Signed-off-by: David Howells <dhowells@redhat.com>
> cc: linux-pci@vger.kernel.org

Acked-by: Bjorn Helgaas <bhelgaas@google.com>

> ---
>
> drivers/pci/pci-sysfs.c | 9 +++++++++
> drivers/pci/proc.c | 8 +++++++-
> drivers/pci/syscall.c | 2 +-
> 3 files changed, 17 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
> index 25d010d449a3..f70b3668036f 100644
> --- a/drivers/pci/pci-sysfs.c
> +++ b/drivers/pci/pci-sysfs.c
> @@ -727,6 +727,9 @@ static ssize_t pci_write_config(struct file *filp, struct kobject *kobj,
> loff_t init_off = off;
> u8 *data = (u8 *) buf;
>
> + if (kernel_is_locked_down())
> + return -EPERM;
> +
> if (off > dev->cfg_size)
> return 0;
> if (off + count > dev->cfg_size) {
> @@ -1018,6 +1021,9 @@ static int pci_mmap_resource(struct kobject *kobj, struct bin_attribute *attr,
> resource_size_t start, end;
> int i;
>
> + if (kernel_is_locked_down())
> + return -EPERM;
> +
> for (i = 0; i < PCI_ROM_RESOURCE; i++)
> if (res == &pdev->resource[i])
> break;
> @@ -1117,6 +1123,9 @@ static ssize_t pci_write_resource_io(struct file *filp, struct kobject *kobj,
> struct bin_attribute *attr, char *buf,
> loff_t off, size_t count)
> {
> + if (kernel_is_locked_down())
> + 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 f82710a8694d..139d6f09ae7b 100644
> --- a/drivers/pci/proc.c
> +++ b/drivers/pci/proc.c
> @@ -116,6 +116,9 @@ static ssize_t proc_bus_pci_write(struct file *file, const char __user *buf,
> int size = dev->cfg_size;
> int cnt;
>
> + if (kernel_is_locked_down())
> + return -EPERM;
> +
> if (pos >= size)
> return 0;
> if (nbytes >= size)
> @@ -195,6 +198,9 @@ static long proc_bus_pci_ioctl(struct file *file, unsigned int cmd,
> #endif /* HAVE_PCI_MMAP */
> int ret = 0;
>
> + if (kernel_is_locked_down())
> + return -EPERM;
> +
> switch (cmd) {
> case PCIIOC_CONTROLLER:
> ret = pci_domain_nr(dev->bus);
> @@ -233,7 +239,7 @@ 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, write_combine;
>
> - if (!capable(CAP_SYS_RAWIO))
> + if (!capable(CAP_SYS_RAWIO) || kernel_is_locked_down())
> 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 9bf993e1f71e..c09524738ceb 100644
> --- a/drivers/pci/syscall.c
> +++ b/drivers/pci/syscall.c
> @@ -92,7 +92,7 @@ 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) || kernel_is_locked_down())
> return -EPERM;
>
> dev = pci_get_bus_and_slot(bus, dfn);
>

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