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parisc: Ensure userspace privilege for ptraced processes in regset functions 

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>
This commit is contained in:
Helge Deller 2019-07-04 03:44:17 +02:00
parent 10835c8546
commit 34c32fc603
1 changed files with 2 additions and 1 deletions
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3
arch/parisc/kernel/ptrace.c
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@ -504,7 +504,8 @@ static void set_reg(struct pt_regs *regs, int num, unsigned long val)
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;