linux-kernel - [PATCH 11/27] x86: Lock down IO port access when the kernel is locked down

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Date:   Thu, 19 Oct 2017 15:51:56 +0100
From:   David Howells <dhowells@...hat.com>
To:     linux-security-module@...r.kernel.org
Cc:     gnomes@...rguk.ukuu.org.uk, linux-efi@...r.kernel.org,
        matthew.garrett@...ula.com, gregkh@...uxfoundation.org,
        linux-kernel@...r.kernel.org, dhowells@...hat.com,
        jforbes@...hat.com
Subject: [PATCH 11/27] x86: Lock down IO port access when the kernel is
 locked down

From: Matthew Garrett <matthew.garrett@...ula.com>

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 <matthew.garrett@...ula.com>
Signed-off-by: David Howells <dhowells@...hat.com>
Reviewed-by: Thomas Gleixner <tglx@...utronix.de>
cc: x86@...nel.org
---

 arch/x86/kernel/ioport.c |    6 ++++--
 drivers/char/mem.c       |    2 ++
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/ioport.c b/arch/x86/kernel/ioport.c
index 9c3cf0944bce..2c0f058651c5 100644
--- a/arch/x86/kernel/ioport.c
+++ b/arch/x86/kernel/ioport.c
@@ -30,7 +30,8 @@ asmlinkage long sys_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) ||
+			kernel_is_locked_down("ioperm")))
 		return -EPERM;
 
 	/*
@@ -120,7 +121,8 @@ 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) ||
+		    kernel_is_locked_down("iopl"))
 			return -EPERM;
 	}
 	regs->flags = (regs->flags & ~X86_EFLAGS_IOPL) |
diff --git a/drivers/char/mem.c b/drivers/char/mem.c
index b7c36898b689..0875b3d47773 100644
--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -768,6 +768,8 @@ static loff_t memory_lseek(struct file *file, loff_t offset, int orig)
 
 static int open_port(struct inode *inode, struct file *filp)
 {
+	if (kernel_is_locked_down("Direct ioport access"))
+		return -EPERM;
 	return capable(CAP_SYS_RAWIO) ? 0 : -EPERM;
 }