Re: [PATCH V34 12/29] x86: Lock down IO port access when the kernel is locked down

Kees Cook
2019-06-22T23:58:26Z

On Fri, Jun 21, 2019 at 05:03:41PM -0700, Matthew Garrett wrote:
> From: Matthew Garrett <mjg59@srcf.ucam.org>
>
> IO port access would permit users to gain access to PCI configuration
> registers, which in turn (on a lot of hardware) give access to MMIO
> register space. This would potentially permit root to trigger arbitrary
> DMA, so lock it down by default.
>
> This also implicitly locks down the KDADDIO, KDDELIO, KDENABIO and
> KDDISABIO console ioctls.
>
> Signed-off-by: Matthew Garrett <mjg59@google.com>

Reviewed-by: Kees Cook <keescook@chromium.org>

-Kees

> Signed-off-by: David Howells <dhowells@redhat.com>
> cc: x86@kernel.org
> ---
> arch/x86/kernel/ioport.c | 7 +++++--
> include/linux/security.h | 1 +
> security/lockdown/lockdown.c | 1 +
> 3 files changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kernel/ioport.c b/arch/x86/kernel/ioport.c
> index 0fe1c8782208..61a89d3c0382 100644
> --- a/arch/x86/kernel/ioport.c
> +++ b/arch/x86/kernel/ioport.c
> @@ -11,6 +11,7 @@
> #include <linux/errno.h>
> #include <linux/types.h>
> #include <linux/ioport.h>
> +#include <linux/security.h>
> #include <linux/smp.h>
> #include <linux/stddef.h>
> #include <linux/slab.h>
> @@ -31,7 +32,8 @@ long ksys_ioperm(unsigned long from, unsigned long num, int turn_on)
>
> if ((from + num <= from) || (from + num > IO_BITMAP_BITS))
> return -EINVAL;
> - if (turn_on && !capable(CAP_SYS_RAWIO))
> + if (turn_on && (!capable(CAP_SYS_RAWIO) ||
> + security_locked_down(LOCKDOWN_IOPORT)))
> return -EPERM;
>
> /*
> @@ -126,7 +128,8 @@ SYSCALL_DEFINE1(iopl, unsigned int, level)
> return -EINVAL;
> /* Trying to gain more privileges? */
> if (level > old) {
> - if (!capable(CAP_SYS_RAWIO))
> + if (!capable(CAP_SYS_RAWIO) ||
> + security_locked_down(LOCKDOWN_IOPORT))
> return -EPERM;
> }
> regs->flags = (regs->flags & ~X86_EFLAGS_IOPL) |
> diff --git a/include/linux/security.h b/include/linux/security.h
> index 1b849f10dec6..60569b7e9465 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -87,6 +87,7 @@ enum lockdown_reason {
> LOCKDOWN_KEXEC,
> LOCKDOWN_HIBERNATION,
> LOCKDOWN_PCI_ACCESS,
> + LOCKDOWN_IOPORT,
> LOCKDOWN_INTEGRITY_MAX,
> LOCKDOWN_CONFIDENTIALITY_MAX,
> };
> diff --git a/security/lockdown/lockdown.c b/security/lockdown/lockdown.c
> index e2ee8a16b94c..895ef3ba1b4c 100644
> --- a/security/lockdown/lockdown.c
> +++ b/security/lockdown/lockdown.c
> @@ -23,6 +23,7 @@ static char *lockdown_reasons[LOCKDOWN_CONFIDENTIALITY_MAX+1] = {
> [LOCKDOWN_KEXEC] = "kexec of unsigned images",
> [LOCKDOWN_HIBERNATION] = "hibernation",
> [LOCKDOWN_PCI_ACCESS] = "direct PCI access",
> + [LOCKDOWN_IOPORT] = "raw io port access",
> [LOCKDOWN_INTEGRITY_MAX] = "integrity",
> [LOCKDOWN_CONFIDENTIALITY_MAX] = "confidentiality",
> };
> --
> 2.22.0.410.gd8fdbe21b5-goog
>

--
Kees Cook