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

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Date:   Sat, 22 Jun 2019 16:58:22 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Matthew Garrett <matthewgarrett@...gle.com>
Cc:     jmorris@...ei.org, linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
        Matthew Garrett <mjg59@...f.ucam.org>,
        Matthew Garrett <mjg59@...gle.com>,
        David Howells <dhowells@...hat.com>, x86@...nel.org
Subject: Re: [PATCH V34 12/29] x86: Lock down IO port access when the kernel
 is locked down

On Fri, Jun 21, 2019 at 05:03:41PM -0700, Matthew Garrett wrote:
> From: Matthew Garrett <mjg59@...f.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@...gle.com>

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

-Kees

> Signed-off-by: David Howells <dhowells@...hat.com>
> cc: x86@...nel.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