/*
* 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
* Copyright (C) 2009 Frederic Weisbecker <fweisbec@gmail.com>
*
* Authors: Alan Stern <stern@rowland.harvard.edu>
* K.Prasad <prasad@linux.vnet.ibm.com>
* Frederic Weisbecker <fweisbec@gmail.com>
*/
/*
* HW_breakpoint: a unified kernel/user-space hardware breakpoint facility,
* using the CPU's debug registers.
*/
#include <linux/perf_event.h>
#include <linux/hw_breakpoint.h>
#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>
/* Per cpu debug control register value */
DEFINE_PER_CPU(unsigned long, cpu_dr7);
EXPORT_PER_CPU_SYMBOL(cpu_dr7);
/* Per cpu debug address registers values */
static DEFINE_PER_CPU(unsigned long, cpu_debugreg[HBP_NUM]);
/*
* Stores the breakpoints currently in use on each breakpoint address
* register for each cpus
*/
static DEFINE_PER_CPU(struct perf_event *, bp_per_reg[HBP_NUM]);
static inline 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));
return bp_info;
}
/*
* Encode the length, type, Exact, and Enable bits for a particular breakpoint
* as stored in debug register 7.
*/
unsigned long encode_dr7(int drnum, unsigned int len, unsigned int type)
{
return __encode_dr7(drnum, len, type) | DR_GLOBAL_SLOWDOWN;
}
/*
* Decode the length and type bits for a particular breakpoint as
* stored in debug register 7. Return the "enabled" status.
*/
int decode_dr7(unsigned long dr7, int bpnum, unsigned *len, unsigned *type)
{
int bp_info = dr7 >> (DR_CONTROL_SHIFT + bpnum * DR_CONTROL_SIZE);
*len = (bp_info & 0xc) | 0x40;
*type = (bp_info & 0x3) | 0x80;
return (dr7 >> (bpnum * DR_ENABLE_SIZE)) & 0x3;
}
/*
* Install a perf counter breakpoint.
*
* We seek a free debug address register and use it for this
* breakpoint. Eventually we enable it in the debug control register.
*
* Atomic: we hold the counter->ctx->lock and we only handle variables
* and registers local to this cpu.
*/
int arch_install_hw_breakpoint(struct perf_event *bp)
{
struct arch_hw_breakpoint *info = counter_arch_bp(bp);
unsigned long *dr7;
int i;
for (i = 0; i < HBP_NUM; i++) {
struct perf_event **slot = &__get_cpu_var(bp_per_reg[i]);
if (!*slot) {
*slot = bp;
break;
}
}
if (WARN_ONCE(i == HBP_NUM, "Can't find any breakpoint slot"))
return -EBUSY;
set_debugreg(info->address, i);
__get_cpu_var(cpu_debugreg[i]) = info->address;
dr7 = &__get_cpu_var(cpu_dr7);
*dr7 |= encode_dr7(i, info->len, info->type);
set_debugreg(*dr7, 7);
return 0;
}
/*
* Uninstall the breakpoint contained in the given counter.
*
* First we search the debug address register it uses and then we disable
* it.
*
* Atomic: we hold the counter->ctx->lock and we only handle variables
* and registers local to this cpu.
*/
void arch_uninstall_hw_breakpoint(struct perf_event *bp)
{
struct arch_hw_breakpoint *info = counter_arch_bp(bp);
unsigned long *dr7;
int i;
for (i = 0; i < HBP_NUM; i++) {
struct perf_event **slot = &__get_cpu_var(bp_per_reg[i]);
if (*slot == bp) {
*slot = NULL;
break;
}
}
if (WARN_ONCE(i == HBP_NUM, "Can't find any breakpoint slot"))
return;
dr7 = &__get_cpu_var(cpu_dr7);
*dr7 &= ~__encode_dr7(i, info->len, info->type);
set_debugreg(*dr7, 7);
}
static int get_hbp_len(u8 hbp_len)
{
unsigned int len_in_bytes = 0;
switch (hbp_len) {
case X86_BREAKPOINT_LEN_1:
len_in_bytes = 1;
break;
case X86_BREAKPOINT_LEN_2:
len_in_bytes = 2;
break;
case X86_BREAKPOINT_LEN_4:
len_in_bytes = 4;
break;
#ifdef CONFIG_X86_64
case X86_BREAKPOINT_LEN_8:
len_in_bytes = 8;
break;
#endif
}
return len_in_bytes;
}
/*
* Check for virtual address in kernel space.
*/
int arch_check_bp_in_kernelspace(struct perf_event *bp)
{
unsigned int len;
unsigned long va;
struct arch_hw_breakpoint *info = counter_arch_bp(bp);
va = info->address;
len = get_hbp_len(info->len);
return (va >= TASK_SIZE) && ((va + len - 1) >= TASK_SIZE);
}
int arch_bp_generic_fields(int x86_len, int x86_type,
int *gen_len, int *gen_type)
{
/* Type */
switch (x86_type) {
case X86_BREAKPOINT_EXECUTE:
if (x86_len != X86_BREAKPOINT_LEN_X)
return -EINVAL;
*gen_type = HW_BREAKPOINT_X;
*gen_len = sizeof(long);
return 0;
case X86_BREAKPOINT_WRITE:
*gen_type = HW_BREAKPOINT_W;
break;
case X86_BREAKPOINT_RW:
*gen_type = HW_BREAKPOINT_W | HW_BREAKPOINT_R;
break;
default:
return -EINVAL;
}
/* Len */
switch (x86_len) {
case X86_BREAKPOINT_LEN_1:
*gen_len = HW_BREAKPOINT_LEN_1;
break;
case X86_BREAKPOINT_LEN_2:
*gen_len = HW_BREAKPOINT_LEN_2;
break;
case X86_BREAKPOINT_LEN_4:
*gen_len = HW_BREAKPOINT_LEN_4;
break;
#ifdef CONFIG_X86_64
case X86_BREAKPOINT_LEN_8:
*gen_len = HW_BREAKPOINT_LEN_8;
break;
#endif
default:
return -EINVAL;
}
return 0;
}
static int arch_build_bp_info(struct perf_event *bp)
{
struct arch_hw_breakpoint *info = counter_arch_bp(bp);
info->address = bp->attr.bp_addr;
/* Type */
switch (bp->attr.bp_type) {
case HW_BREAKPOINT_W:
info->type = X86_BREAKPOINT_WRITE;
break;
case HW_BREAKPOINT_W | HW_BREAKPOINT_R:
info->type = X86_BREAKPOINT_RW;
break;
case HW_BREAKPOINT_X:
info->type = X86_BREAKPOINT_EXECUTE;
/*
* x86 inst breakpoints need to have a specific undefined len.
* But we still need to check userspace is not trying to setup
* an unsupported length, to get a range breakpoint for example.
*/
if (bp->attr.bp_len == sizeof(long)) {
info->len = X86_BREAKPOINT_LEN_X;
return 0;
}
default:
return -EINVAL;
}
/* Len */
switch (bp->attr.bp_len) {
case HW_BREAKPOINT_LEN_1:
info->len = X86_BREAKPOINT_LEN_1;
break;
case HW_BREAKPOINT_LEN_2:
info->len = X86_BREAKPOINT_LEN_2;
break;
case HW_BREAKPOINT_LEN_4:
info->len = X86_BREAKPOINT_LEN_4;
break;
#ifdef CONFIG_X86_64
case HW_BREAKPOINT_LEN_8:
info->len = X86_BREAKPOINT_LEN_8;
break;
#endif
default:
return -EINVAL;
}
return 0;
}
/*
* Validate the arch-specific HW Breakpoint register settings
*/
int arch_validate_hwbkpt_settings(struct perf_event *bp)
{
struct arch_hw_breakpoint *info = counter_arch_bp(bp);
unsigned int align;
int ret;
ret = arch_build_bp_info(bp);
if (ret)
return ret;
ret = -EINVAL;
switch (info->len) {
case X86_BREAKPOINT_LEN_1:
align = 0;
break;
case X86_BREAKPOINT_LEN_2:
align = 1;
break;
case X86_BREAKPOINT_LEN_4:
align = 3;
break;
#ifdef CONFIG_X86_64
case X86_BREAKPOINT_LEN_8:
align = 7;
break;
#endif
default:
return ret;
}
/*
* Check that the low-order bits of the address are appropriate
* for the alignment implied by len.
*/
if (info->address & align)
return -EINVAL;
return 0;
}
/*
* Dump the debug register contents to the user.
* We can't dump our per cpu values because it
* may contain cpu wide breakpoint, something that
* doesn't belong to the current task.
*
* TODO: include non-ptrace user breakpoints (perf)
*/
void aout_dump_debugregs(struct user *dump)
{
int i;
int dr7 = 0;
struct perf_event *bp;
struct arch_hw_breakpoint *info;
struct thread_struct *thread = ¤t->thread;
for (i = 0; i < HBP_NUM; i++) {
bp = thread->ptrace_bps[i];
if (bp && !bp->attr.disabled) {
dump->u_debugreg[i] = bp->attr.bp_addr;
info = counter_arch_bp(bp);
dr7 |= encode_dr7(i, info->len, info->type);
} else {
dump->u_debugreg[i] = 0;
}
}
dump->u_debugreg[4] = 0;
dump->u_debugreg[5] = 0;
dump->u_debugreg[6] = current->thread.debugreg6;
dump->u_debugreg[7] = dr7;
}
EXPORT_SYMBOL_GPL(aout_dump_debugregs);
/*
* Release the user breakpoints used by ptrace
*/
void flush_ptrace_hw_breakpoint(struct task_struct *tsk)
{
int i;
struct thread_struct *t = &tsk->thread;
for (i = 0; i < HBP_NUM; i++) {
unregister_hw_breakpoint(t->ptrace_bps[i]);
t->ptrace_bps[i] = NULL;
}
}
void hw_breakpoint_restore(void)
{
set_debugreg(__get_cpu_var(cpu_debugreg[0]), 0);
set_debugreg(__get_cpu_var(cpu_debugreg[1]), 1);
set_debugreg(__get_cpu_var(cpu_debugreg[2]), 2);
set_debugreg(__get_cpu_var(cpu_debugreg[3]), 3);
set_debugreg(current->thread.debugreg6, 6);
set_debugreg(__get_cpu_var(cpu_dr7), 7);
}
EXPORT_SYMBOL_GPL(hw_breakpoint_restore);
/*
* 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
*
*/
static int __kprobes hw_breakpoint_handler(struct die_args *args)
{
int i, cpu, rc = NOTIFY_STOP;
struct perf_event *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;
/* If it's a single step, TRAP bits are random */
if (dr6 & DR_STEP)
return NOTIFY_DONE;
/* Do an early return if no trap bits are set in DR6 */
if ((dr6 & DR_TRAP_BITS) == 0)
return NOTIFY_DONE;
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;
/*
* The counter may be concurrently released but that can only
* occur from a call_rcu() path. We can then safely fetch
* the breakpoint, use its callback, touch its counter
* while we are in an rcu_read_lock() path.
*/
rcu_read_lock();
bp = per_cpu(bp_per_reg[i], cpu);
/*
* 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 concurrent perf counter removing.
*/
if (!bp) {
rcu_read_unlock();
break;
}
perf_bp_event(bp, args->regs);
/*
* Set up resume flag to avoid breakpoint recursion when
* returning back to origin.
*/
if (bp->hw.info.type == X86_BREAKPOINT_EXECUTE)
args->regs->flags |= X86_EFLAGS_RF;
rcu_read_unlock();
}
/*
* Further processing in do_debug() is needed for a) user-space
* breakpoints (to generate signals) and b) when the system has
* taken exception due to multiple causes
*/
if ((current->thread.debugreg6 & DR_TRAP_BITS) ||
(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);
}
void hw_breakpoint_pmu_read(struct perf_event *bp)
{
/* TODO */
}
