linux_dsm_epyc7002/arch/x86/kernel/ioport.c

// SPDX-License-Identifier: GPL-2.0
/*
 * This contains the io-permission bitmap code - written by obz, with changes
 * by Linus. 32/64 bits code unification by Miguel Botón.
 */
#include <linux/capability.h>
#include <linux/security.h>
#include <linux/syscalls.h>
#include <linux/bitmap.h>
#include <linux/ioport.h>
#include <linux/sched.h>
#include <linux/slab.h>

#include <asm/io_bitmap.h>
#include <asm/desc.h>

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;
	set_tsk_thread_flag(tsk, TIF_IO_BITMAP);
}

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();
	if (iobm && refcount_dec_and_test(&iobm->refcnt))
		kfree(iobm);
}

/*
 * this changes the io permissions bitmap in the current task.
 */
long ksys_ioperm(unsigned long from, unsigned long num, int turn_on)
{
	struct thread_struct *t = &current->thread;
	unsigned int i, max_long;
	struct io_bitmap *iobm;

	if ((from + num <= from) || (from + num > IO_BITMAP_BITS))
		return -EINVAL;
	if (turn_on && (!capable(CAP_SYS_RAWIO) ||
			security_locked_down(LOCKDOWN_IOPORT)))
		return -EPERM;

	/*
	 * If it's the first ioperm() call in this thread's lifetime, set the
	 * IO bitmap up. ioperm() is much less timing critical than clone(),
	 * this is why we delay this operation until now:
	 */
	iobm = t->io_bitmap;
	if (!iobm) {
		/* No point to allocate a bitmap just to clear permissions */
		if (!turn_on)
			return 0;
		iobm = kmalloc(sizeof(*iobm), GFP_KERNEL);
		if (!iobm)
			return -ENOMEM;

		memset(iobm->bitmap, 0xff, sizeof(iobm->bitmap));
		refcount_set(&iobm->refcnt, 1);
	}

	/*
	 * If the bitmap is not shared, then nothing can take a refcount as
	 * current can obviously not fork at the same time. If it's shared
	 * duplicate it and drop the refcount on the original one.
	 */
	if (refcount_read(&iobm->refcnt) > 1) {
		iobm = kmemdup(iobm, sizeof(*iobm), GFP_KERNEL);
		if (!iobm)
			return -ENOMEM;
		refcount_set(&iobm->refcnt, 1);
		io_bitmap_exit();
	}

	/*
	 * Store the bitmap pointer (might be the same if the task already
	 * head one). Must be done here so freeing the bitmap when all
	 * permissions are dropped has the pointer set up.
	 */
	t->io_bitmap = iobm;
	/* Mark it active for context switching and exit to user mode */
	set_thread_flag(TIF_IO_BITMAP);

	/*
	 * Update the tasks bitmap. The update of the TSS bitmap happens on
	 * exit to user mode. So this needs no protection.
	 */
	if (turn_on)
		bitmap_clear(iobm->bitmap, from, num);
	else
		bitmap_set(iobm->bitmap, from, num);

	/*
	 * Search for a (possibly new) maximum. This is simple and stupid,
	 * to keep it obviously correct:
	 */
	max_long = UINT_MAX;
	for (i = 0; i < IO_BITMAP_LONGS; i++) {
		if (iobm->bitmap[i] != ~0UL)
			max_long = i;
	}
	/* All permissions dropped? */
	if (max_long == UINT_MAX) {
		io_bitmap_exit();
		return 0;
	}

	iobm->max = (max_long + 1) * sizeof(unsigned long);

	/*
	 * Update the sequence number to force a TSS update on return to
	 * user mode.
	 */
	iobm->sequence = atomic64_add_return(1, &io_bitmap_sequence);

	return 0;
}

SYSCALL_DEFINE3(ioperm, unsigned long, from, unsigned long, num, int, turn_on)
{
	return ksys_ioperm(from, num, turn_on);
}

/*
 * sys_iopl has to be used when you want to access the IO ports
 * beyond the 0x3ff range: to get the full 65536 ports bitmapped
 * you'd need 8kB of bitmaps/process, which is a bit excessive.
 *
 * Here we just change the flags value on the stack: we allow
 * only the super-user to do it. This depends on the stack-layout
 * on system-call entry - see also fork() and the signal handling
 * code.
 */
SYSCALL_DEFINE1(iopl, unsigned int, level)
{
	struct pt_regs *regs = current_pt_regs();
	struct thread_struct *t = &current->thread;

	/*
	 * 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 (level > 3)
		return -EINVAL;
	/* Trying to gain more privileges? */
	if (level > old) {
		if (!capable(CAP_SYS_RAWIO) ||
		    security_locked_down(LOCKDOWN_IOPORT))
			return -EPERM;
	}
	regs->flags = (regs->flags & ~X86_EFLAGS_IOPL) |
		(level << X86_EFLAGS_IOPL_BIT);
	t->iopl = level << X86_EFLAGS_IOPL_BIT;
	set_iopl_mask(t->iopl);

	return 0;
}