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    Subject[PATCH 4.19 253/271] parisc: Ensure userspace privilege for ptraced processes in regset functions
    Date
    From: Helge Deller <deller@gmx.de>

    commit 34c32fc603311a72cb558e5e337555434f64c27b upstream.

    On parisc the privilege level of a process is stored in the lowest two bits of
    the instruction pointers (IAOQ0 and IAOQ1). On Linux we use privilege level 0
    for the kernel and privilege level 3 for user-space. So userspace should not be
    allowed to modify IAOQ0 or IAOQ1 of a ptraced process to change it's privilege
    level to e.g. 0 to try to gain kernel privileges.

    This patch prevents such modifications in the regset support functions by
    always setting the two lowest bits to one (which relates to privilege level 3
    for user-space) if IAOQ0 or IAOQ1 are modified via ptrace regset calls.

    Link: https://bugs.gentoo.org/481768
    Cc: <stable@vger.kernel.org> # v4.7+
    Tested-by: Rolf Eike Beer <eike-kernel@sf-tec.de>
    Signed-off-by: Helge Deller <deller@gmx.de>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    arch/parisc/kernel/ptrace.c | 3 ++-
    1 file changed, 2 insertions(+), 1 deletion(-)

    --- a/arch/parisc/kernel/ptrace.c
    +++ b/arch/parisc/kernel/ptrace.c
    @@ -496,7 +496,8 @@ static void set_reg(struct pt_regs *regs
    return;
    case RI(iaoq[0]):
    case RI(iaoq[1]):
    - regs->iaoq[num - RI(iaoq[0])] = val;
    + /* set 2 lowest bits to ensure userspace privilege: */
    + regs->iaoq[num - RI(iaoq[0])] = val | 3;
    return;
    case RI(sar): regs->sar = val;
    return;

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