path: root/arch/mips/kernel/unaligned.c

/*
 * Handle unaligned accesses by emulation.
 *
 * This file is subject to the terms and conditions of the GNU General Public
 * License.  See the file "COPYING" in the main directory of this archive
 * for more details.
 *
 * Copyright (C) 1996, 1998, 1999, 2002 by Ralf Baechle
 * Copyright (C) 1999 Silicon Graphics, Inc.
 * Copyright (C) 2014 Imagination Technologies Ltd.
 *
 * This file contains exception handler for address error exception with the
 * special capability to execute faulting instructions in software.  The
 * handler does not try to handle the case when the program counter points
 * to an address not aligned to a word boundary.
 *
 * Putting data to unaligned addresses is a bad practice even on Intel where
 * only the performance is affected.  Much worse is that such code is non-
 * portable.  Due to several programs that die on MIPS due to alignment
 * problems I decided to implement this handler anyway though I originally
 * didn't intend to do this at all for user code.
 *
 * For now I enable fixing of address errors by default to make life easier.
 * I however intend to disable this somewhen in the future when the alignment
 * problems with user programs have been fixed.	 For programmers this is the
 * right way to go.
 *
 * Fixing address errors is a per process option.  The option is inherited
 * across fork(2) and execve(2) calls.	If you really want to use the
 * option in your user programs - I discourage the use of the software
 * emulation strongly - use the following code in your userland stuff:
 *
 * #include <sys/sysmips.h>
 *
 * ...
 * sysmips(MIPS_FIXADE, x);
 * ...
 *
 * The argument x is 0 for disabling software emulation, enabled otherwise.
 *
 * Below a little program to play around with this feature.
 *
 * #include <stdio.h>
 * #include <sys/sysmips.h>
 *
 * struct foo {
 *	   unsigned char bar[8];
 * };
 *
 * main(int argc, char *argv[])
 * {
 *	   struct foo x = {0, 1, 2, 3, 4, 5, 6, 7};
 *	   unsigned int *p = (unsigned int *) (x.bar + 3);
 *	   int i;
 *
 *	   if (argc > 1)
 *		   sysmips(MIPS_FIXADE, atoi(argv[1]));
 *
 *	   printf("*p = %08lx\n", *p);
 *
 *	   *p = 0xdeadface;
 *
 *	   for(i = 0; i <= 7; i++)
 *	   printf("%02x ", x.bar[i]);
 *	   printf("\n");
 * }
 *
 * Coprocessor loads are not supported; I think this case is unimportant
 * in the practice.
 *
 * TODO: Handle ndc (attempted store to doubleword in uncached memory)
 *	 exception for the R6000.
 *	 A store crossing a page boundary might be executed only partially.
 *	 Undo the partial store in this case.
 */
#include <linux/context_tracking.h>
#include <linux/mm.h>
#include <linux/signal.h>
#include <linux/smp.h>
#include <linux/sched.h>
#include <linux/debugfs.h>
#include <linux/perf_event.h>

#include <asm/asm.h>
#include <asm/branch.h>
#include <asm/byteorder.h>
#include <asm/cop2.h>
#include <asm/debug.h>
#include <asm/fpu.h>
#include <asm/fpu_emulator.h>
#include <asm/inst.h>
#include <asm/unaligned-emul.h>
#include <asm/mmu_context.h>
#include <linux/uaccess.h>

#include "access-helper.h"

enum {
	UNALIGNED_ACTION_QUIET,
	UNALIGNED_ACTION_SIGNAL,
	UNALIGNED_ACTION_SHOW,
};
#ifdef CONFIG_DEBUG_FS
static u32 unaligned_instructions;
static u32 unaligned_action;
#else
#define unaligned_action UNALIGNED_ACTION_QUIET
#endif
extern void show_registers(struct pt_regs *regs);

static void emulate_load_store_insn(struct pt_regs *regs,
	void __user *addr, unsigned int *pc)
{
	unsigned long origpc, orig31, value;
	union mips_instruction insn;
	unsigned int res;
	bool user = user_mode(regs);

	origpc = (unsigned long)pc;
	orig31 = regs->regs[31];

	perf_sw_event(PERF_COUNT_SW_EMULATION_FAULTS, 1, regs, 0);

	/*
	 * This load never faults.
	 */
	__get_inst32(&insn.word, pc, user);

	switch (insn.i_format.opcode) {
		/*
		 * These are instructions that a compiler doesn't generate.  We
		 * can assume therefore that the code is MIPS-aware and
		 * really buggy.  Emulating these instructions would break the
		 * semantics anyway.
		 */
	case ll_op:
	case lld_op:
	case sc_op:
	case scd_op:

		/*
		 * For these instructions the only way to create an address
		 * error is an attempted access to kernel/supervisor address
		 * space.
		 */
	case ldl_op:
	case ldr_op:
	case lwl_op:
	case lwr_op:
	case sdl_op:
	case sdr_op:
	case swl_op:
	case swr_op:
	case lb_op:
	case lbu_op:
	case sb_op:
		goto sigbus;

		/*
		 * The remaining opcodes are the ones that are really of
		 * interest.
		 */
	case spec3_op:
		if (insn.dsp_format.func == lx_op) {
			switch (insn.dsp_format.op) {
			case lwx_op:
				if (user && !access_ok(addr, 4))
					goto sigbus;
				LoadW(addr, value, res);
				if (res)
					goto fault;
				compute_return_epc(regs);
				regs->regs[insn.dsp_format.rd] = value;
				break;
			case lhx_op:
				if (user && !access_ok(addr, 2))
					goto sigbus;
				LoadHW(addr, value, res);
				if (res)
					goto fault;
				compute_return_epc(regs);
				regs->regs[insn.dsp_format.rd] = value;
				break;
			default:
				goto sigill;
			}
		}
#ifdef CONFIG_EVA
		else {
			/*
			 * we can land here only from kernel accessing user
			 * memory, so we need to "switch" the address limit to
			 * user space, so that address check can work properly.
			 */
			switch (insn.spec3_format.func) {
			case lhe_op:
				if (!access_ok(addr, 2))
					goto sigbus;
				LoadHWE(addr, value, res);
				if (res)
					goto fault;
				compute_return_epc(regs);
				regs->regs[insn.spec3_format.rt] = value;
				break;
			case lwe_op:
				if (!access_ok(addr, 4))
					goto sigbus;
				LoadWE(addr, value, res);
				if (res)
					goto fault;
				compute_return_epc(regs);
				regs->regs[insn.spec3_format.rt] = value;
				break;
			case lhue_op:
				if (!access_ok(addr, 2))
					goto sigbus;
				LoadHWUE(addr, value, res);
				if (res)
					goto fault;
				compute_return_epc(regs);
				regs->regs[insn.spec3_format.rt] = value;
				break;
			case she_op:
				if (!access_ok(addr, 2))
					goto sigbus;
				compute_return_epc(regs);
				value = regs->regs[insn.spec3_format.rt];
				StoreHWE(addr, value, res);
				if (res)
					goto fault;
				break;
			case swe_op:
				if (!access_ok(addr, 4))
					goto sigbus;
				compute_return_epc(regs);
				value = regs-&g