/*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
*
* Copyright (C) 2007 Alan Stern
* Copyright (C) 2009 IBM Corporation
*/
/*
* HW_breakpoint: a unified kernel/user-space hardware breakpoint facility,
* using the CPU's debug registers.
*/
#include <linux/irqflags.h>
#include <linux/notifier.h>
#include <linux/kallsyms.h>
#include <linux/kprobes.h>
#include <linux/percpu.h>
#include <linux/kdebug.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/sched.h>
#include <linux/init.h>
#include <linux/smp.h>
#include <asm/hw_breakpoint.h>
#include <asm/processor.h>
#include <asm/debugreg.h>
/* Unmasked kernel DR7 value */
static unsigned long kdr7;
/*
* Masks for the bits corresponding to registers DR0 - DR3 in DR7 register.
* Used to clear and verify the status of bits corresponding to DR0 - DR3
*/
static const unsigned long dr7_masks[HBP_NUM] = {
0x000f0003, /* LEN0, R/W0, G0, L0 */
0x00f0000c, /* LEN1, R/W1, G1, L1 */
0x0f000030, /* LEN2, R/W2, G2, L2 */
0xf00000c0 /* LEN3, R/W3, G3, L3 */
};
/*
* Encode the length, type, Exact, and Enable bits for a particular breakpoint
* as stored in debug register 7.
*/
static unsigned long encode_dr7(int drnum, unsigned int len, unsigned int type)
{
unsigned long bp_info;
bp_info = (len | type) & 0xf;
bp_info <<= (DR_CONTROL_SHIFT + drnum * DR_CONTROL_SIZE);
bp_info |= (DR_GLOBAL_ENABLE << (drnum * DR_ENABLE_SIZE)) |
DR_GLOBAL_SLOWDOWN;
return bp_info;
}
void arch_update_kernel_hw_breakpoint(void *unused)
{
struct hw_breakpoint *bp;
int i, cpu = get_cpu();
unsigned long temp_kdr7 = 0;
/* Don't allow debug exceptions while we update the registers */
set_debugreg(0UL, 7);
for (i = hbp_kernel_pos; i < HBP_NUM; i++) {
per_cpu(this_hbp_kernel[i], cpu) = bp = hbp_kernel[i];
if (bp) {
temp_kdr7 |= encode_dr7(i, bp->info.len, bp->info.type);
set_debugreg(bp->info.address, i);
}
}
/* No need to set DR6. Update the debug registers with kernel-space
* breakpoint values from kdr7 and user-space requests from the
* current process
*/
kdr7 = temp_kdr7;
set_debugreg(kdr7 | current->thread.debugreg7, 7);
put_cpu();
}
/*
* Install the thread breakpoints in their debug registers.
*/
void arch_install_thread_hw_breakpoint(struct task_struct *tsk)
{
struct thread_struct *thread = &(tsk->thread);
switch (hbp_kernel_pos) {
case 4:
set_debugreg(thread->debugreg[3], 3);
case 3:
set_debugreg(thread->debugreg[2], 2);
case 2:
set_debugreg(thread->debugreg[1], 1);
case 1:
set_debugreg(thread->debugreg[0], 0);
default:
break;
}
/* No need to set DR6 */
set_debugreg((kdr7 | thread->debugreg7), 7);
}
/*
* Install the debug register values for just the kernel, no thread.
*/
void arch_uninstall_thread_hw_breakpoint()
{
/* Clear the user-space portion of debugreg7 by setting only kdr7 */
set_debugreg(kdr7, 7);
}
static int get_hbp_len(u8 hbp_len)
{
unsigned int len_in_bytes = 0;
switch (hbp_len) {
case HW_BREAKPOINT_LEN_1:
len_in_bytes = 1;
break;
case HW_BREAKPOINT_LEN_2:
len_in_bytes = 2;
break;
case HW_BREAKPOINT_LEN_4:
len_in_bytes = 4;
break;
#ifdef CONFIG_X86_64
case HW_BREAKPOINT_LEN_8:
len_in_bytes = 8;
break;
#endif
}
return len_in_bytes;
}
/*
* Check for virtual address in user space.
*/
int arch_check_va_in_userspace(unsigned long va, u8 hbp_len)
{
unsigned int len;
len = get_hbp_len(hbp_len);
return (va <= TASK_SIZE - len);
}
/*
* Check for virtual address in kernel space.
*/
int arch_check_va_in_kernelspace(unsigned long va, u8 hbp_len)
{
unsigned int len;
len = get_hbp_len(hbp_len);
return (va >= TASK_SIZE) && ((va + len - 1) >= TASK_SIZE);
}
/*
* Store a breakpoint's encoded address, length, and type.
*/
static int arch_store_info(struct hw_breakpoint *bp, struct task_struct *tsk)
{
/*
* User-space requests will always have the address field populated
* Symbol names from user-space are rejected
*/
if (tsk && bp->info.name)
return -EINVAL;
/*
* For kernel-addresses, either the address or symbol name can be
* specified.
*/
if (bp->info.name)
bp->info.address = (unsigned long)
kallsyms_lookup_name(bp->info.name);
if (bp->info.address)
return 0;
return -EINVAL;
}
/*
* Validate the arch-specific HW Breakpoint register settings
*/
int arch_validate_hwbkpt_settings(struct hw_breakpoint *bp,
struct task_struct *tsk)
{
unsigned int align;
int ret = -EINVAL;
switch (bp->info.type) {
/*
* Ptrace-refactoring code
* For now, we'll allow instruction breakpoint only for user-space
* addresses
*/
case HW_BREAKPOINT_EXECUTE:
if ((!arch_check_va_in_userspace(bp->info.address,
bp->info.len)) &&
bp->info.len != HW_BREAKPOINT_LEN_EXECUTE)
return ret;
break;
case HW_BREAKPOINT_WRITE:
break;
case HW_BREAKPOINT_RW:
break;
default:
return ret;
}
switch (bp->info.len) {
case HW_BREAKPOINT_LEN_1:
align = 0;
break;
case HW_BREAKPOINT_LEN_2:
align = 1;
break;
case HW_BREAKPOINT_LEN_4:
align = 3;
break;
#ifdef CONFIG_X86_64
case HW_BREAKPOINT_LEN_8:
align = 7;
break;
#endif
default:
return ret;
}
if (bp->triggered)
ret = arch_store_info(bp, tsk);
if (ret < 0)
return ret;
/*
* Check that the low-order bits of the address are appropriate
* for the alignment implied by len.
*/
if (bp->info.address & align)
return -EINVAL;
/* Check that the virtual address is in the proper range */
if (tsk) {
if (!arch_check_va_in_userspace(bp->info.address, bp->info.len))
return -EFAULT;
} else {
if (!arch_check_va_in_kernelspace(bp->info.address,
bp->info.len))
return -EFAULT;
}
return 0;
}
void arch_update_user_hw_breakpoint(int pos, struct task_struct *tsk)
{
struct thread_struct *thread = &(tsk->thread);
struct hw_breakpoint *bp = thread->hbp[pos];
thread->debugreg7 &= ~dr7_masks[pos];
if (bp) {
thread->debugreg[pos] = bp->info.address;
thread->debugreg7 |= encode_dr7(pos, bp->info.len,
bp->info.type);
} else
thread->debugreg[pos] = 0;
}
void arch_flush_thread_hw_breakpoint(struct task_struct *tsk)
{
int i;
struct thread_struct *thread = &(tsk->thread);
thread->debugreg7 = 0;
for (i = 0; i < HBP_NUM; i++)
thread->debugreg[i] = 0;
}
/*
* Handle debug exception notifications.
*
* Return value is either NOTIFY_STOP or NOTIFY_DONE as explained below.
*
* NOTIFY_DONE returned if one of the following conditions is true.
* i) When the causative address is from user-space and the exception
* is a valid one, i.e. not triggered as a result of lazy debug register
* switching
* ii) When there are more bits than trap<n> set in DR6 register (such
* as BD, BS or BT) indicating that more than one debug condition is
* met and requires some more action in do_debug().
*
* NOTIFY_STOP returned for all other cases
*
*/
int __kprobes hw_breakpoint_handler(struct die_args *args)
{
int i, cpu, rc = NOTIFY_STOP;
struct hw_breakpoint *bp;
unsigned long dr7, dr6;
unsigned long *dr6_p;
/* The DR6 value is pointed by args->err */
dr6_p = (unsigned long *)ERR_PTR(args->err);
dr6 = *dr6_p;
/* Do an early return if no trap bits are set in DR6 */
if ((dr6 & DR_TRAP_BITS) == 0)
return NOTIFY_DONE;
/* Lazy debug register switching */
if (!test_tsk_thread_flag(current, TIF_DEBUG))
arch_uninstall_thread_hw_breakpoint();
get_debugreg(dr7, 7);
/* Disable breakpoints during exception handling */
set_debugreg(0UL, 7);
/*
* Assert that local interrupts are disabled
* Reset the DRn bits in the virtualized register value.
* The ptrace trigger routine will add in whatever is needed.
*/
current->thread.debugreg6 &= ~DR_TRAP_BITS;
cpu = get_cpu();
/* Handle all the breakpoints that were triggered */
for (i = 0; i < HBP_NUM; ++i) {
if (likely(!(dr6 & (DR_TRAP0 << i))))
continue;
/*
* Find the corresponding hw_breakpoint structure and
* invoke its triggered callback.
*/
if (i >= hbp_kernel_pos)
bp = per_cpu(this_hbp_kernel[i], cpu);
else {
bp = current->thread.hbp[i];
if (bp)
rc = NOTIFY_DONE;
}
/*
* Reset the 'i'th TRAP bit in dr6 to denote completion of
* exception handling
*/
(*dr6_p) &= ~(DR_TRAP0 << i);
/*
* bp can be NULL due to lazy debug register switching
* or due to the delay between updates of hbp_kernel_pos
* and this_hbp_kernel.
*/
if (!bp)
continue;
(bp->triggered)(bp, args->regs);
}
if (dr6 & (~DR_TRAP_BITS))
rc = NOTIFY_DONE;
set_debugreg(dr7, 7);
put_cpu();
return rc;
}
/*
* Handle debug exception notifications.
*/
int __kprobes hw_breakpoint_exceptions_notify(
struct notifier_block *unused, unsigned long val, void *data)
{
if (val != DIE_DEBUG)
return NOTIFY_DONE;
return hw_breakpoint_handler(data);
}
