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Commit 1deb9c5d authored by Chris Metcalf's avatar Chris Metcalf
Browse files

arch/tile: don't allow user code to set the PL via ptrace or signal return 



The kernel was allowing any component of the pt_regs to be updated either
by signal handlers writing to the stack, or by processes writing via
PTRACE_POKEUSR or PTRACE_SETREGS, which meant they could set their PL
up from 0 to 1 and get access to kernel code and data (or, in practice,
cause a kernel panic).  We now always reset the ex1 field, allowing the
user to set their ICS bit only.

Signed-off-by: default avatarChris Metcalf <cmetcalf@tilera.com>
parent 34a89d26

arch/tile/kernel/ptrace.c

+21 −18
Original line number Diff line number Diff line
@@ -50,10 +50,10 @@ long arch_ptrace(struct task_struct *child, long request, 
{

	unsigned long __user *datap = (long __user __force *)data;

	unsigned long tmp;

	int i;

	long ret = -EIO;

	unsigned long *childregs;

	char *childreg;

	struct pt_regs copyregs;

	int ex1_offset;



	switch (request) {
@@ -80,6 +80,16 @@ long arch_ptrace(struct task_struct *child, long request, 
		if (addr >= PTREGS_SIZE)

			break;

		childreg = (char *)task_pt_regs(child) + addr;



		/* Guard against overwrites of the privilege level. */

		ex1_offset = PTREGS_OFFSET_EX1;

#if defined(CONFIG_COMPAT) && defined(__BIG_ENDIAN)

		if (is_compat_task())   /* point at low word */

			ex1_offset += sizeof(compat_long_t);

#endif

		if (addr == ex1_offset)

			data = PL_ICS_EX1(USER_PL, EX1_ICS(data));



#ifdef CONFIG_COMPAT

		if (is_compat_task()) {

			if (addr & (sizeof(compat_long_t)-1))
@@ -96,26 +106,19 @@ long arch_ptrace(struct task_struct *child, long request, 
		break;



	case PTRACE_GETREGS:  /* Get all registers from the child. */

		if (!access_ok(VERIFY_WRITE, datap, PTREGS_SIZE))

			break;

		childregs = (long *)task_pt_regs(child);

		for (i = 0; i < sizeof(struct pt_regs)/sizeof(unsigned long);

				++i) {

			ret = __put_user(childregs[i], &datap[i]);

			if (ret != 0)

				break;

		if (copy_to_user(datap, task_pt_regs(child),

				 sizeof(struct pt_regs)) == 0) {

			ret = 0;

		}

		break;



	case PTRACE_SETREGS:  /* Set all registers in the child. */

		if (!access_ok(VERIFY_READ, datap, PTREGS_SIZE))

			break;

		childregs = (long *)task_pt_regs(child);

		for (i = 0; i < sizeof(struct pt_regs)/sizeof(unsigned long);

				++i) {

			ret = __get_user(childregs[i], &datap[i]);

			if (ret != 0)

				break;

		if (copy_from_user(&copyregs, datap,

				   sizeof(struct pt_regs)) == 0) {

			copyregs.ex1 =

				PL_ICS_EX1(USER_PL, EX1_ICS(copyregs.ex1));

			*task_pt_regs(child) = copyregs;

			ret = 0;

		}

		break;

arch/tile/kernel/signal.c

+3 −0
Original line number Diff line number Diff line
@@ -71,6 +71,9 @@ int restore_sigcontext(struct pt_regs *regs, 
	for (i = 0; i < sizeof(struct pt_regs)/sizeof(long); ++i)

		err |= __get_user(regs->regs[i], &sc->gregs[i]);



	/* Ensure that the PL is always set to USER_PL. */

	regs->ex1 = PL_ICS_EX1(USER_PL, EX1_ICS(regs->ex1));



	regs->faultnum = INT_SWINT_1_SIGRETURN;



	err |= __get_user(*pr0, &sc->gregs[0]);