arch/arm/kernel/swp_emulate.c - linux - Git at Google

 /*
  *  linux/arch/arm/kernel/swp_emulate.c
  *
  *  Copyright (C) 2009 ARM Limited
  *  __user_* functions adapted from include/asm/uaccess.h
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 2 as
  * published by the Free Software Foundation.
  *
  *  Implements emulation of the SWP/SWPB instructions using load-exclusive and
  *  store-exclusive for processors that have them disabled (or future ones that
  *  might not implement them).
  *
  *  Syntax of SWP{B} instruction: SWP{B}<c> <Rt>, <Rt2>, [<Rn>]
  *  Where: Rt  = destination
  *	   Rt2 = source
  *	   Rn  = address
  */

 #include <linux/init.h>
 #include <linux/kernel.h>
 #include <linux/proc_fs.h>
 #include <linux/sched.h>
 #include <linux/syscalls.h>
 #include <linux/perf_event.h>

 #include <asm/opcodes.h>
 #include <asm/traps.h>
 #include <asm/uaccess.h>

 /*
  * Error-checking SWP macros implemented using ldrex{b}/strex{b}
  */
 #define __user_swpX_asm(data, addr, res, temp, B)		\
 	__asm__ __volatile__(					\
 	"	mov		%2, %1\n"			\
 	"0:	ldrex"B"	%1, [%3]\n"			\
 	"1:	strex"B"	%0, %2, [%3]\n"			\
 	"	cmp		%0, #0\n"			\
 	"	movne		%0, %4\n"			\
 	"2:\n"							\
 	"	.section	 .fixup,\"ax\"\n"		\
 	"	.align		2\n"				\
 	"3:	mov		%0, %5\n"			\
 	"	b		2b\n"				\
 	"	.previous\n"					\
 	"	.section	 __ex_table,\"a\"\n"		\
 	"	.align		3\n"				\
 	"	.long		0b, 3b\n"			\
 	"	.long		1b, 3b\n"			\
 	"	.previous"					\
 	: "=&r" (res), "+r" (data), "=&r" (temp)		\
 	: "r" (addr), "i" (-EAGAIN), "i" (-EFAULT)		\
 	: "cc", "memory")

 #define __user_swp_asm(data, addr, res, temp) \
 	__user_swpX_asm(data, addr, res, temp, "")
 #define __user_swpb_asm(data, addr, res, temp) \
 	__user_swpX_asm(data, addr, res, temp, "b")

 /*
  * Macros/defines for extracting register numbers from instruction.
  */
 #define EXTRACT_REG_NUM(instruction, offset) \
 	(((instruction) & (0xf << (offset))) >> (offset))
 #define RN_OFFSET  16
 #define RT_OFFSET  12
 #define RT2_OFFSET  0
 /*
  * Bit 22 of the instruction encoding distinguishes between
  * the SWP and SWPB variants (bit set means SWPB).
  */
 #define TYPE_SWPB (1 << 22)

 static unsigned long swpcounter;
 static unsigned long swpbcounter;
 static unsigned long abtcounter;
 static pid_t         previous_pid;

 #ifdef CONFIG_PROC_FS
 static int proc_read_status(char *page, char **start, off_t off, int count,
 			    int *eof, void *data)
 {
 	char *p = page;
 	int len;

 	p += sprintf(p, "Emulated SWP:\t\t%lu\n", swpcounter);
 	p += sprintf(p, "Emulated SWPB:\t\t%lu\n", swpbcounter);
 	p += sprintf(p, "Aborted SWP{B}:\t\t%lu\n", abtcounter);
 	if (previous_pid != 0)
 		p += sprintf(p, "Last process:\t\t%d\n", previous_pid);

 	len = (p - page) - off;
 	if (len < 0)
 		len = 0;

 	*eof = (len <= count) ? 1 : 0;
 	*start = page + off;

 	return len;
 }
 #endif

 /*
  * Set up process info to signal segmentation fault - called on access error.
  */
 static void set_segfault(struct pt_regs *regs, unsigned long addr)
 {
 	siginfo_t info;

 	down_read(&current->mm->mmap_sem);
 	if (find_vma(current->mm, addr) == NULL)
 		info.si_code = SEGV_MAPERR;
 	else
 		info.si_code = SEGV_ACCERR;
 	up_read(&current->mm->mmap_sem);

 	info.si_signo = SIGSEGV;
 	info.si_errno = 0;
 	info.si_addr  = (void *) instruction_pointer(regs);

 	pr_debug("SWP{B} emulation: access caused memory abort!\n");
 	arm_notify_die("Illegal memory access", regs, &info, 0, 0);

 	abtcounter++;
 }

 static int emulate_swpX(unsigned int address, unsigned int *data,
 			unsigned int type)
 {
 	unsigned int res = 0;

 	if ((type != TYPE_SWPB) && (address & 0x3)) {
 		/* SWP to unaligned address not permitted */
 		pr_debug("SWP instruction on unaligned pointer!\n");
 		return -EFAULT;
 	}

 	while (1) {
 		unsigned long temp;

 		/*
 		 * Barrier required between accessing protected resource and
 		 * releasing a lock for it. Legacy code might not have done
 		 * this, and we cannot determine that this is not the case
 		 * being emulated, so insert always.
 		 */
 		smp_mb();

 		if (type == TYPE_SWPB)
 			__user_swpb_asm(*data, address, res, temp);
 		else
 			__user_swp_asm(*data, address, res, temp);

 		if (likely(res != -EAGAIN) || signal_pending(current))
 			break;

 		cond_resched();
 	}

 	if (res == 0) {
 		/*
 		 * Barrier also required between acquiring a lock for a
 		 * protected resource and accessing the resource. Inserted for
 		 * same reason as above.
 		 */
 		smp_mb();

 		if (type == TYPE_SWPB)
 			swpbcounter++;
 		else
 			swpcounter++;
 	}

 	return res;
 }

 /*
  * swp_handler logs the id of calling process, dissects the instruction, sanity
  * checks the memory location, calls emulate_swpX for the actual operation and
  * deals with fixup/error handling before returning
  */
 static int swp_handler(struct pt_regs *regs, unsigned int instr)
 {
 	unsigned int address, destreg, data, type;
 	unsigned int res = 0;

 	perf_sw_event(PERF_COUNT_SW_EMULATION_FAULTS, 1, regs, regs->ARM_pc);

 	res = arm_check_condition(instr, regs->ARM_cpsr);
 	switch (res) {
 	case ARM_OPCODE_CONDTEST_PASS:
 		break;
 	case ARM_OPCODE_CONDTEST_FAIL:
 		/* Condition failed - return to next instruction */
 		regs->ARM_pc += 4;
 		return 0;
 	case ARM_OPCODE_CONDTEST_UNCOND:
 		/* If unconditional encoding - not a SWP, undef */
 		return -EFAULT;
 	default:
 		return -EINVAL;
 	}

 	if (current->pid != previous_pid) {
 		pr_debug("\"%s\" (%ld) uses deprecated SWP{B} instruction\n",
 			 current->comm, (unsigned long)current->pid);
 		previous_pid = current->pid;
 	}

 	address = regs->uregs[EXTRACT_REG_NUM(instr, RN_OFFSET)];
 	data	= regs->uregs[EXTRACT_REG_NUM(instr, RT2_OFFSET)];
 	destreg = EXTRACT_REG_NUM(instr, RT_OFFSET);

 	type = instr & TYPE_SWPB;

 	pr_debug("addr in r%d->0x%08x, dest is r%d, source in r%d->0x%08x)\n",
 		 EXTRACT_REG_NUM(instr, RN_OFFSET), address,
 		 destreg, EXTRACT_REG_NUM(instr, RT2_OFFSET), data);

 	/* Check access in reasonable access range for both SWP and SWPB */
 	if (!access_ok(VERIFY_WRITE, (address & ~3), 4)) {
 		pr_debug("SWP{B} emulation: access to %p not allowed!\n",
 			 (void *)address);
 		res = -EFAULT;
 	} else {
 		res = emulate_swpX(address, &data, type);
 	}

 	if (res == 0) {
 		/*
 		 * On successful emulation, revert the adjustment to the PC
 		 * made in kernel/traps.c in order to resume execution at the
 		 * instruction following the SWP{B}.
 		 */
 		regs->ARM_pc += 4;
 		regs->uregs[destreg] = data;
 	} else if (res == -EFAULT) {
 		/*
 		 * Memory errors do not mean emulation failed.
 		 * Set up signal info to return SEGV, then return OK
 		 */
 		set_segfault(regs, address);
 	}

 	return 0;
 }

 /*
  * Only emulate SWP/SWPB executed in ARM state/User mode.
  * The kernel must be SWP free and SWP{B} does not exist in Thumb/ThumbEE.
  */
 static struct undef_hook swp_hook = {
 	.instr_mask = 0x0fb00ff0,
 	.instr_val  = 0x01000090,
 	.cpsr_mask  = MODE_MASK | PSR_T_BIT | PSR_J_BIT,
 	.cpsr_val   = USR_MODE,
 	.fn	    = swp_handler
 };

 /*
  * Register handler and create status file in /proc/cpu
  * Invoked as late_initcall, since not needed before init spawned.
  */
 static int __init swp_emulation_init(void)
 {
 #ifdef CONFIG_PROC_FS
 	struct proc_dir_entry *res;

 	res = create_proc_entry("cpu/swp_emulation", S_IRUGO, NULL);

 	if (!res)
 		return -ENOMEM;

 	res->read_proc = proc_read_status;
 #endif /* CONFIG_PROC_FS */

 	printk(KERN_NOTICE "Registering SWP/SWPB emulation handler\n");
 	register_undef_hook(&swp_hook);

 	return 0;
 }

 late_initcall(swp_emulation_init);
	/*
	* linux/arch/arm/kernel/swp_emulate.c
	*
	* Copyright (C) 2009 ARM Limited
	* __user_* functions adapted from include/asm/uaccess.h
	*
	* This program is free software; you can redistribute it and/or modify
	* it under the terms of the GNU General Public License version 2 as
	* published by the Free Software Foundation.
	*
	* Implements emulation of the SWP/SWPB instructions using load-exclusive and
	* store-exclusive for processors that have them disabled (or future ones that
	* might not implement them).
	*
	* Syntax of SWP{B} instruction: SWP{B}<c> <Rt>, <Rt2>, [<Rn>]
	* Where: Rt = destination
	* Rt2 = source
	* Rn = address
	*/

	#include <linux/init.h>
	#include <linux/kernel.h>
	#include <linux/proc_fs.h>
	#include <linux/sched.h>
	#include <linux/syscalls.h>
	#include <linux/perf_event.h>

	#include <asm/opcodes.h>
	#include <asm/traps.h>
	#include <asm/uaccess.h>

	/*
	* Error-checking SWP macros implemented using ldrex{b}/strex{b}
	*/
	#define __user_swpX_asm(data, addr, res, temp, B) \
	__asm__ __volatile__( \
	" mov %2, %1\n" \
	"0: ldrex"B" %1, [%3]\n" \
	"1: strex"B" %0, %2, [%3]\n" \
	" cmp %0, #0\n" \
	" movne %0, %4\n" \
	"2:\n" \
	" .section .fixup,\"ax\"\n" \
	" .align 2\n" \
	"3: mov %0, %5\n" \
	" b 2b\n" \
	" .previous\n" \
	" .section __ex_table,\"a\"\n" \
	" .align 3\n" \
	" .long 0b, 3b\n" \
	" .long 1b, 3b\n" \
	" .previous" \
	: "=&r" (res), "+r" (data), "=&r" (temp) \
	: "r" (addr), "i" (-EAGAIN), "i" (-EFAULT) \
	: "cc", "memory")

	#define __user_swp_asm(data, addr, res, temp) \
	__user_swpX_asm(data, addr, res, temp, "")
	#define __user_swpb_asm(data, addr, res, temp) \
	__user_swpX_asm(data, addr, res, temp, "b")

	/*
	* Macros/defines for extracting register numbers from instruction.
	*/
	#define EXTRACT_REG_NUM(instruction, offset) \
	(((instruction) & (0xf << (offset))) >> (offset))
	#define RN_OFFSET 16
	#define RT_OFFSET 12
	#define RT2_OFFSET 0
	/*
	* Bit 22 of the instruction encoding distinguishes between
	* the SWP and SWPB variants (bit set means SWPB).
	*/
	#define TYPE_SWPB (1 << 22)

	static unsigned long swpcounter;
	static unsigned long swpbcounter;
	static unsigned long abtcounter;
	static pid_t previous_pid;

	#ifdef CONFIG_PROC_FS
	static int proc_read_status(char page, char *start, off_t off, int count,
	int eof, void data)
	{
	char *p = page;
	int len;

	p += sprintf(p, "Emulated SWP:\t\t%lu\n", swpcounter);
	p += sprintf(p, "Emulated SWPB:\t\t%lu\n", swpbcounter);
	p += sprintf(p, "Aborted SWP{B}:\t\t%lu\n", abtcounter);
	if (previous_pid != 0)
	p += sprintf(p, "Last process:\t\t%d\n", previous_pid);

	len = (p - page) - off;
	if (len < 0)
	len = 0;

	*eof = (len <= count) ? 1 : 0;
	*start = page + off;

	return len;
	}
	#endif

	/*
	* Set up process info to signal segmentation fault - called on access error.
	*/
	static void set_segfault(struct pt_regs *regs, unsigned long addr)
	{
	siginfo_t info;

	down_read(&current->mm->mmap_sem);
	if (find_vma(current->mm, addr) == NULL)
	info.si_code = SEGV_MAPERR;
	else
	info.si_code = SEGV_ACCERR;
	up_read(&current->mm->mmap_sem);

	info.si_signo = SIGSEGV;
	info.si_errno = 0;
	info.si_addr = (void *) instruction_pointer(regs);

	pr_debug("SWP{B} emulation: access caused memory abort!\n");
	arm_notify_die("Illegal memory access", regs, &info, 0, 0);

	abtcounter++;
	}

	static int emulate_swpX(unsigned int address, unsigned int *data,
	unsigned int type)
	{
	unsigned int res = 0;

	if ((type != TYPE_SWPB) && (address & 0x3)) {
	/* SWP to unaligned address not permitted */
	pr_debug("SWP instruction on unaligned pointer!\n");
	return -EFAULT;
	}

	while (1) {
	unsigned long temp;

	/*
	* Barrier required between accessing protected resource and
	* releasing a lock for it. Legacy code might not have done
	* this, and we cannot determine that this is not the case
	* being emulated, so insert always.
	*/
	smp_mb();

	if (type == TYPE_SWPB)
	__user_swpb_asm(*data, address, res, temp);
	else
	__user_swp_asm(*data, address, res, temp);

	if (likely(res != -EAGAIN) \|\| signal_pending(current))
	break;

	cond_resched();
	}

	if (res == 0) {
	/*
	* Barrier also required between acquiring a lock for a
	* protected resource and accessing the resource. Inserted for
	* same reason as above.
	*/
	smp_mb();

	if (type == TYPE_SWPB)
	swpbcounter++;
	else
	swpcounter++;
	}

	return res;
	}

	/*
	* swp_handler logs the id of calling process, dissects the instruction, sanity
	* checks the memory location, calls emulate_swpX for the actual operation and
	* deals with fixup/error handling before returning
	*/
	static int swp_handler(struct pt_regs *regs, unsigned int instr)
	{
	unsigned int address, destreg, data, type;
	unsigned int res = 0;

	perf_sw_event(PERF_COUNT_SW_EMULATION_FAULTS, 1, regs, regs->ARM_pc);

	res = arm_check_condition(instr, regs->ARM_cpsr);
	switch (res) {
	case ARM_OPCODE_CONDTEST_PASS:
	break;
	case ARM_OPCODE_CONDTEST_FAIL:
	/* Condition failed - return to next instruction */
	regs->ARM_pc += 4;
	return 0;
	case ARM_OPCODE_CONDTEST_UNCOND:
	/* If unconditional encoding - not a SWP, undef */
	return -EFAULT;
	default:
	return -EINVAL;
	}

	if (current->pid != previous_pid) {
	pr_debug("\"%s\" (%ld) uses deprecated SWP{B} instruction\n",
	current->comm, (unsigned long)current->pid);
	previous_pid = current->pid;
	}

	address = regs->uregs[EXTRACT_REG_NUM(instr, RN_OFFSET)];
	data = regs->uregs[EXTRACT_REG_NUM(instr, RT2_OFFSET)];
	destreg = EXTRACT_REG_NUM(instr, RT_OFFSET);

	type = instr & TYPE_SWPB;

	pr_debug("addr in r%d->0x%08x, dest is r%d, source in r%d->0x%08x)\n",
	EXTRACT_REG_NUM(instr, RN_OFFSET), address,
	destreg, EXTRACT_REG_NUM(instr, RT2_OFFSET), data);

	/* Check access in reasonable access range for both SWP and SWPB */
	if (!access_ok(VERIFY_WRITE, (address & ~3), 4)) {
	pr_debug("SWP{B} emulation: access to %p not allowed!\n",
	(void *)address);
	res = -EFAULT;
	} else {
	res = emulate_swpX(address, &data, type);
	}

	if (res == 0) {
	/*
	* On successful emulation, revert the adjustment to the PC
	* made in kernel/traps.c in order to resume execution at the
	* instruction following the SWP{B}.
	*/
	regs->ARM_pc += 4;
	regs->uregs[destreg] = data;
	} else if (res == -EFAULT) {
	/*
	* Memory errors do not mean emulation failed.
	* Set up signal info to return SEGV, then return OK
	*/
	set_segfault(regs, address);
	}

	return 0;
	}

	/*
	* Only emulate SWP/SWPB executed in ARM state/User mode.
	* The kernel must be SWP free and SWP{B} does not exist in Thumb/ThumbEE.
	*/
	static struct undef_hook swp_hook = {
	.instr_mask = 0x0fb00ff0,
	.instr_val = 0x01000090,
	.cpsr_mask = MODE_MASK \| PSR_T_BIT \| PSR_J_BIT,
	.cpsr_val = USR_MODE,
	.fn = swp_handler
	};

	/*
	* Register handler and create status file in /proc/cpu
	* Invoked as late_initcall, since not needed before init spawned.
	*/
	static int __init swp_emulation_init(void)
	{
	#ifdef CONFIG_PROC_FS
	struct proc_dir_entry *res;

	res = create_proc_entry("cpu/swp_emulation", S_IRUGO, NULL);

	if (!res)
	return -ENOMEM;

	res->read_proc = proc_read_status;
	#endif /* CONFIG_PROC_FS */

	printk(KERN_NOTICE "Registering SWP/SWPB emulation handler\n");
	register_undef_hook(&swp_hook);

	return 0;
	}

	late_initcall(swp_emulation_init);