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


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