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32ef1b30ad
restore_sigcontext() copies the whole supervision register (SR) from the
signal frame and only clears SPR_SR_SM before the value is reloaded into
the hardware SR (through ESR and l.rfe) on the return to user space. All
other SR bits are left under user control.
An unprivileged task can thus return from a signal handler through a
crafted sigframe that clears SPR_SR_DME. With the data MMU disabled the
CPU performs no translation or protection on data accesses, so the task
gains read and write access to arbitrary physical memory, a local
privilege escalation. SPR_SR_IME, SPR_SR_SUMRA, SPR_SR_LEE, SPR_SR_EPH
and the cache-enable bits are exposed the same way. The ptrace GPR regset
already refuses any change to SR for exactly this reason.
Restore only the arithmetic flag bits (F, CY, OV) from the signal frame
and take every privileged control bit from the SR the kernel saved on
signal entry.
Verified with qemu-system-or1k -M or1k-sim: before this change an
unprivileged PoC clears SPR_SR_DME in rt_sigreturn and writes a marker to
physical address 0x03000000 (beyond the kernel's mem=32M); afterwards the
same PoC receives SIGSEGV and physical memory is unchanged.
Fixes: ac689eb7f9 ("OpenRISC: Signal handling")
Cc: stable@vger.kernel.org
Signed-off-by: Ali Ahmet Memis <ali@iusegentoo.com>
Signed-off-by: Stafford Horne <shorne@gmail.com>
85 lines
2.5 KiB
C
85 lines
2.5 KiB
C
/* SPDX-License-Identifier: GPL-2.0-or-later */
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/*
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* OpenRISC Linux
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*
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* Linux architectural port borrowing liberally from similar works of
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* others. All original copyrights apply as per the original source
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* declaration.
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*
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* OpenRISC implementation:
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* Copyright (C) 2003 Matjaz Breskvar <phoenix@bsemi.com>
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* Copyright (C) 2010-2011 Jonas Bonn <jonas@southpole.se>
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* et al.
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*/
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#ifndef __ASM_OPENRISC_PROCESSOR_H
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#define __ASM_OPENRISC_PROCESSOR_H
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#include <asm/spr_defs.h>
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#include <asm/page.h>
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#include <asm/ptrace.h>
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#define STACK_TOP TASK_SIZE
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#define STACK_TOP_MAX STACK_TOP
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/* Kernel and user SR register setting */
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#define KERNEL_SR (SPR_SR_DME | SPR_SR_IME | SPR_SR_ICE \
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| SPR_SR_DCE | SPR_SR_SM)
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#define USER_SR (SPR_SR_DME | SPR_SR_IME | SPR_SR_ICE \
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| SPR_SR_DCE | SPR_SR_IEE | SPR_SR_TEE)
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/* SR bits user space may change via sigreturn, the rest stay kernel owned */
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#define SPR_SR_USER_MASK (SPR_SR_F | SPR_SR_CY | SPR_SR_OV)
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/*
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* User space process size. This is hardcoded into a few places,
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* so don't change it unless you know what you are doing.
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*/
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#define TASK_SIZE (0x80000000UL)
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/* This decides where the kernel will search for a free chunk of vm
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* space during mmap's.
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*/
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#define TASK_UNMAPPED_BASE (TASK_SIZE / 8 * 3)
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#ifndef __ASSEMBLER__
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struct task_struct;
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struct thread_struct {
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long fpcsr; /* Floating point control status register. */
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};
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/*
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* At user->kernel entry, the pt_regs struct is stacked on the top of the
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* kernel-stack. This macro allows us to find those regs for a task.
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* Notice that subsequent pt_regs stackings, like recursive interrupts
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* occurring while we're in the kernel, won't affect this - only the first
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* user->kernel transition registers are reached by this (i.e. not regs
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* for running signal handler)
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*/
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#define user_regs(thread_info) (((struct pt_regs *)((unsigned long)(thread_info) + THREAD_SIZE - STACK_FRAME_OVERHEAD)) - 1)
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/*
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* Dito but for the currently running task
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*/
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#define task_pt_regs(task) user_regs(task_thread_info(task))
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#define INIT_SP (sizeof(init_stack) + (unsigned long) &init_stack)
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#define INIT_THREAD { }
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#define KSTK_EIP(tsk) (task_pt_regs(tsk)->pc)
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#define KSTK_ESP(tsk) (task_pt_regs(tsk)->sp)
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void start_thread(struct pt_regs *regs, unsigned long nip, unsigned long sp);
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unsigned long __get_wchan(struct task_struct *p);
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void show_registers(struct pt_regs *regs);
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#define cpu_relax() barrier()
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#endif /* __ASSEMBLER__ */
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#endif /* __ASM_OPENRISC_PROCESSOR_H */
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