[PATCH 04/12] x86: Lock down IO port access when securelevel is enabled

Matthew Garrett
2013-09-09T15:52:21Z

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 when securelevel is set.

Signed-off-by: Matthew Garrett <matthew.garrett@nebula.com>
---
arch/x86/kernel/ioport.c | 5 +++--
drivers/char/mem.c | 7 +++++++
2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/ioport.c b/arch/x86/kernel/ioport.c
index 4ddaf66..2a9ccd4 100644
--- a/arch/x86/kernel/ioport.c
+++ b/arch/x86/kernel/ioport.c
@@ -15,6 +15,7 @@
#include <linux/thread_info.h>
#include <linux/syscalls.h>
#include <linux/bitmap.h>
+#include <linux/security.h>
#include <asm/syscalls.h>

/*
@@ -28,7 +29,7 @@ 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) || (get_securelevel() > 0)))
return -EPERM;

/*
@@ -103,7 +104,7 @@ 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) || (get_securelevel() > 0))
return -EPERM;
}
regs->flags = (regs->flags & ~X86_EFLAGS_IOPL) | (level << 12);
diff --git a/drivers/char/mem.c b/drivers/char/mem.c
index f895a8c..741f536 100644
--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -28,6 +28,7 @@
#include <linux/export.h>
#include <linux/io.h>
#include <linux/aio.h>
+#include <linux/security.h>

#include <asm/uaccess.h>

@@ -545,6 +546,9 @@ static ssize_t read_port(struct file *file, char __user *buf,
unsigned long i = *ppos;
char __user *tmp = buf;

+ if (get_securelevel() > 0)
+ return -EPERM;
+
if (!access_ok(VERIFY_WRITE, buf, count))
return -EFAULT;
while (count-- > 0 && i < 65536) {
@@ -563,6 +567,9 @@ static ssize_t write_port(struct file *file, const char __user *buf,
unsigned long i = *ppos;
const char __user *tmp = buf;

+ if (get_securelevel() > 0)
+ return -EPERM;
+
if (!access_ok(VERIFY_READ, buf, count))
return -EFAULT;
while (count-- > 0 && i < 65536) {
--
1.8.3.1