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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Rolf Eike Beer <eike-kernel@sf-tec.de>,
        Helge Deller <deller@gmx.de>
Subject: [PATCH 4.19 253/271] parisc: Ensure userspace privilege for ptraced processes in regset functions
Date:   Wed, 24 Jul 2019 21:22:02 +0200
Message-Id: <20190724191716.885680591@linuxfoundation.org>
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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;