x86: Lock down IO port access when securelevel is enabled

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 <mjg59@srcf.ucam.org>
Gbp-Pq: Topic features/all/securelevel
Gbp-Pq: Name x86-lock-down-io-port-access-when-securelevel-is-ena.patch

diff --git a/arch/x86/kernel/ioport.c b/arch/x86/kernel/ioport.c
index 589b3193f1020b8389a5f64b296cff531e85e849..48c888f0ea67b49b81d4a14e0a7126bde8b2f0e3 100644 (file)
--- 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;
 
        /*
@@ -108,7 +109,7 @@ 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) |

diff --git a/drivers/char/mem.c b/drivers/char/mem.c
index 593a8818aca99e345e03d0fb56eabd25b5ffd05a..25cf624a375c74ef0fe436042917eacb31f6b0dc 100644 (file)
--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -28,6 +28,7 @@
 #include <linux/export.h>
 #include <linux/io.h>
 #include <linux/uio.h>
+#include <linux/security.h>
 
 #include <linux/uaccess.h>
 
@@ -587,6 +588,9 @@ 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) {
@@ -605,6 +609,9 @@ 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) {