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x86/iopl: Restrict iopl() permission scope

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The access to the full I/O port range can be also provided by the TSS I/O
bitmap, but that would require to copy 8k of data on scheduling in the
task. As shown with the sched out optimization TSS.io_bitmap_base can be
used to switch the incoming task to a preallocated I/O bitmap which has all
bits zero, i.e. allows access to all I/O ports.

Implementing this allows to provide an iopl() emulation mode which restricts
the IOPL level 3 permissions to I/O port access but removes the STI/CLI
permission which is coming with the hardware IOPL mechansim.

Provide a config option to switch IOPL to emulation mode, make it the
default and while at it also provide an option to disable IOPL completely.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Andy Lutomirski <luto@kernel.org>
This commit is contained in:
Thomas Gleixner
2019-11-11 23:03:28 +01:00
parent be9afb4b52
commit c8137ace56
6 changed files with 137 additions and 45 deletions
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87
arch/x86/kernel/ioport.c
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@@ -17,25 +17,41 @@
static atomic64_t io_bitmap_sequence;
void io_bitmap_share(struct task_struct *tsk)
{
/*
* Take a refcount on current's bitmap. It can be used by
* both tasks as long as none of them changes the bitmap.
*/
refcount_inc(&current->thread.io_bitmap->refcnt);
tsk->thread.io_bitmap = current->thread.io_bitmap;
{
/* Can be NULL when current->thread.iopl_emul == 3 */
if (current->thread.io_bitmap) {
/*
* Take a refcount on current's bitmap. It can be used by
* both tasks as long as none of them changes the bitmap.
*/
refcount_inc(&current->thread.io_bitmap->refcnt);
tsk->thread.io_bitmap = current->thread.io_bitmap;
}
set_tsk_thread_flag(tsk, TIF_IO_BITMAP);
}
static void task_update_io_bitmap(void)
{
struct thread_struct *t = &current->thread;
if (t->iopl_emul == 3 || t->io_bitmap) {
/* TSS update is handled on exit to user space */
set_thread_flag(TIF_IO_BITMAP);
} else {
clear_thread_flag(TIF_IO_BITMAP);
/* Invalidate TSS */
preempt_disable();
tss_update_io_bitmap();
preempt_enable();
}
}
void io_bitmap_exit(void)
{
struct io_bitmap *iobm = current->thread.io_bitmap;
current->thread.io_bitmap = NULL;
clear_thread_flag(TIF_IO_BITMAP);
preempt_disable();
tss_update_io_bitmap();
preempt_enable();
task_update_io_bitmap();
if (iobm && refcount_dec_and_test(&iobm->refcnt))
kfree(iobm);
}
@@ -157,36 +173,55 @@ SYSCALL_DEFINE3(ioperm, unsigned long, from, unsigned long, num, int, turn_on)
*/
SYSCALL_DEFINE1(iopl, unsigned int, level)
{
struct pt_regs *regs = current_pt_regs();
struct thread_struct *t = &current->thread;
struct pt_regs *regs = current_pt_regs();
unsigned int old;
/*
* Careful: the IOPL bits in regs->flags are undefined under Xen PV
* and changing them has no effect.
*/
unsigned int old = t->iopl >> X86_EFLAGS_IOPL_BIT;
if (IS_ENABLED(CONFIG_X86_IOPL_NONE))
return -ENOSYS;
if (level > 3)
return -EINVAL;
if (IS_ENABLED(CONFIG_X86_IOPL_EMULATION))
old = t->iopl_emul;
else
old = t->iopl >> X86_EFLAGS_IOPL_BIT;
/* No point in going further if nothing changes */
if (level == old)
return 0;
/* Trying to gain more privileges? */
if (level > old) {
if (!capable(CAP_SYS_RAWIO) ||
security_locked_down(LOCKDOWN_IOPORT))
return -EPERM;
}
/*
* Change the flags value on the return stack, which has been set
* up on system-call entry. See also the fork and signal handling
* code how this is handled.
*/
regs->flags = (regs->flags & ~X86_EFLAGS_IOPL) |
(level << X86_EFLAGS_IOPL_BIT);
/* Store the new level in the thread struct */
t->iopl = level << X86_EFLAGS_IOPL_BIT;
/*
* X86_32 switches immediately and XEN handles it via emulation.
*/
set_iopl_mask(t->iopl);
if (IS_ENABLED(CONFIG_X86_IOPL_EMULATION)) {
t->iopl_emul = level;
task_update_io_bitmap();
} else {
/*
* Change the flags value on the return stack, which has
* been set up on system-call entry. See also the fork and
* signal handling code how this is handled.
*/
regs->flags = (regs->flags & ~X86_EFLAGS_IOPL) |
(level << X86_EFLAGS_IOPL_BIT);
/* Store the new level in the thread struct */
t->iopl = level << X86_EFLAGS_IOPL_BIT;
/*
* X86_32 switches immediately and XEN handles it via
* emulation.
*/
set_iopl_mask(t->iopl);
}
return 0;
}