linux-kernel - [PATCH V33 13/30] x86: Lock down IO port access when the kernel is locked down

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Date:   Thu, 20 Jun 2019 18:19:24 -0700
From:   Matthew Garrett <matthewgarrett@...gle.com>
To:     jmorris@...ei.org
Cc:     linux-security@...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: [PATCH V33 13/30] x86: Lock down IO port access when the kernel is
 locked down

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>
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..ac0ba0b2f3be 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_is_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_is_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 95aa5ac1fa6b..59f0ac7adfa6 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 ae76a7cce7ba..6e426887bb23 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