Commit 29da4f91 authored by Ravi Bangoria's avatar Ravi Bangoria Committed by Michael Ellerman
Browse files

powerpc/watchpoint: Don't allow concurrent perf and ptrace events 



With Book3s DAWR, ptrace and perf watchpoints on powerpc behaves
differently. Ptrace watchpoint works in one-shot mode and generates
signal before executing instruction. It's ptrace user's job to
single-step the instruction and re-enable the watchpoint. OTOH, in
case of perf watchpoint, kernel emulates/single-steps the instruction
and then generates event. If perf and ptrace creates two events with
same or overlapping address ranges, it's ambiguous to decide who
should single-step the instruction. Because of this issue, don't
allow perf and ptrace watchpoint at the same time if their address
range overlaps.

Signed-off-by: default avatarRavi Bangoria <ravi.bangoria@linux.ibm.com>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
Reviewed-by: default avatarMichael Neuling <mikey@neuling.org>
Link: https://lore.kernel.org/r/20200514111741.97993-15-ravi.bangoria@linux.ibm.com
parent 74c68810

arch/powerpc/include/asm/hw_breakpoint.h

+2 −0
Original line number Diff line number Diff line
@@ -70,6 +70,8 @@ extern int hw_breakpoint_exceptions_notify(struct notifier_block *unused, 
						unsigned long val, void *data);

int arch_install_hw_breakpoint(struct perf_event *bp);

void arch_uninstall_hw_breakpoint(struct perf_event *bp);

int arch_reserve_bp_slot(struct perf_event *bp);

void arch_release_bp_slot(struct perf_event *bp);

void arch_unregister_hw_breakpoint(struct perf_event *bp);

void hw_breakpoint_pmu_read(struct perf_event *bp);

extern void flush_ptrace_hw_breakpoint(struct task_struct *tsk);

arch/powerpc/kernel/hw_breakpoint.c

+221 −0
Original line number Diff line number Diff line
@@ -124,6 +124,227 @@ static bool is_ptrace_bp(struct perf_event *bp) 
	return bp->overflow_handler == ptrace_triggered;

}



struct breakpoint {

	struct list_head list;

	struct perf_event *bp;

	bool ptrace_bp;

};



static DEFINE_PER_CPU(struct breakpoint *, cpu_bps[HBP_NUM_MAX]);

static LIST_HEAD(task_bps);



static struct breakpoint *alloc_breakpoint(struct perf_event *bp)

{

	struct breakpoint *tmp;



	tmp = kzalloc(sizeof(*tmp), GFP_KERNEL);

	if (!tmp)

		return ERR_PTR(-ENOMEM);

	tmp->bp = bp;

	tmp->ptrace_bp = is_ptrace_bp(bp);

	return tmp;

}



static bool bp_addr_range_overlap(struct perf_event *bp1, struct perf_event *bp2)

{

	__u64 bp1_saddr, bp1_eaddr, bp2_saddr, bp2_eaddr;



	bp1_saddr = ALIGN_DOWN(bp1->attr.bp_addr, HW_BREAKPOINT_SIZE);

	bp1_eaddr = ALIGN(bp1->attr.bp_addr + bp1->attr.bp_len, HW_BREAKPOINT_SIZE);

	bp2_saddr = ALIGN_DOWN(bp2->attr.bp_addr, HW_BREAKPOINT_SIZE);

	bp2_eaddr = ALIGN(bp2->attr.bp_addr + bp2->attr.bp_len, HW_BREAKPOINT_SIZE);



	return (bp1_saddr < bp2_eaddr && bp1_eaddr > bp2_saddr);

}



static bool alternate_infra_bp(struct breakpoint *b, struct perf_event *bp)

{

	return is_ptrace_bp(bp) ? !b->ptrace_bp : b->ptrace_bp;

}



static bool can_co_exist(struct breakpoint *b, struct perf_event *bp)

{

	return !(alternate_infra_bp(b, bp) && bp_addr_range_overlap(b->bp, bp));

}



static int task_bps_add(struct perf_event *bp)

{

	struct breakpoint *tmp;



	tmp = alloc_breakpoint(bp);

	if (IS_ERR(tmp))

		return PTR_ERR(tmp);



	list_add(&tmp->list, &task_bps);

	return 0;

}



static void task_bps_remove(struct perf_event *bp)

{

	struct list_head *pos, *q;



	list_for_each_safe(pos, q, &task_bps) {

		struct breakpoint *tmp = list_entry(pos, struct breakpoint, list);



		if (tmp->bp == bp) {

			list_del(&tmp->list);

			kfree(tmp);

			break;

		}

	}

}



/*

 * If any task has breakpoint from alternate infrastructure,

 * return true. Otherwise return false.

 */

static bool all_task_bps_check(struct perf_event *bp)

{

	struct breakpoint *tmp;



	list_for_each_entry(tmp, &task_bps, list) {

		if (!can_co_exist(tmp, bp))

			return true;

	}

	return false;

}



/*

 * If same task has breakpoint from alternate infrastructure,

 * return true. Otherwise return false.

 */

static bool same_task_bps_check(struct perf_event *bp)

{

	struct breakpoint *tmp;



	list_for_each_entry(tmp, &task_bps, list) {

		if (tmp->bp->hw.target == bp->hw.target &&

		    !can_co_exist(tmp, bp))

			return true;

	}

	return false;

}



static int cpu_bps_add(struct perf_event *bp)

{

	struct breakpoint **cpu_bp;

	struct breakpoint *tmp;

	int i = 0;



	tmp = alloc_breakpoint(bp);

	if (IS_ERR(tmp))

		return PTR_ERR(tmp);



	cpu_bp = per_cpu_ptr(cpu_bps, bp->cpu);

	for (i = 0; i < nr_wp_slots(); i++) {

		if (!cpu_bp[i]) {

			cpu_bp[i] = tmp;

			break;

		}

	}

	return 0;

}



static void cpu_bps_remove(struct perf_event *bp)

{

	struct breakpoint **cpu_bp;

	int i = 0;



	cpu_bp = per_cpu_ptr(cpu_bps, bp->cpu);

	for (i = 0; i < nr_wp_slots(); i++) {

		if (!cpu_bp[i])

			continue;



		if (cpu_bp[i]->bp == bp) {

			kfree(cpu_bp[i]);

			cpu_bp[i] = NULL;

			break;

		}

	}

}



static bool cpu_bps_check(int cpu, struct perf_event *bp)

{

	struct breakpoint **cpu_bp;

	int i;



	cpu_bp = per_cpu_ptr(cpu_bps, cpu);

	for (i = 0; i < nr_wp_slots(); i++) {

		if (cpu_bp[i] && !can_co_exist(cpu_bp[i], bp))

			return true;

	}

	return false;

}



static bool all_cpu_bps_check(struct perf_event *bp)

{

	int cpu;



	for_each_online_cpu(cpu) {

		if (cpu_bps_check(cpu, bp))

			return true;

	}

	return false;

}



/*

 * We don't use any locks to serialize accesses to cpu_bps or task_bps

 * because are already inside nr_bp_mutex.

 */

int arch_reserve_bp_slot(struct perf_event *bp)

{

	int ret;



	/* ptrace breakpoint */

	if (is_ptrace_bp(bp)) {

		if (all_cpu_bps_check(bp))

			return -ENOSPC;



		if (same_task_bps_check(bp))

			return -ENOSPC;



		return task_bps_add(bp);

	}



	/* perf breakpoint */

	if (is_kernel_addr(bp->attr.bp_addr))

		return 0;



	if (bp->hw.target && bp->cpu == -1) {

		if (same_task_bps_check(bp))

			return -ENOSPC;



		return task_bps_add(bp);

	} else if (!bp->hw.target && bp->cpu != -1) {

		if (all_task_bps_check(bp))

			return -ENOSPC;



		return cpu_bps_add(bp);

	}



	if (same_task_bps_check(bp))

		return -ENOSPC;



	ret = cpu_bps_add(bp);

	if (ret)

		return ret;

	ret = task_bps_add(bp);

	if (ret)

		cpu_bps_remove(bp);



	return ret;

}



void arch_release_bp_slot(struct perf_event *bp)

{

	if (!is_kernel_addr(bp->attr.bp_addr)) {

		if (bp->hw.target)

			task_bps_remove(bp);

		if (bp->cpu != -1)

			cpu_bps_remove(bp);

	}

}



/*

 * Perform cleanup of arch-specific counters during unregistration

 * of the perf-event

kernel/events/hw_breakpoint.c

+16 −0
Original line number Diff line number Diff line
@@ -213,6 +213,15 @@ toggle_bp_slot(struct perf_event *bp, bool enable, enum bp_type_idx type, 
		list_del(&bp->hw.bp_list);

}



__weak int arch_reserve_bp_slot(struct perf_event *bp)

{

	return 0;

}



__weak void arch_release_bp_slot(struct perf_event *bp)

{

}



/*

 * Function to perform processor-specific cleanup during unregistration

 */
@@ -270,6 +279,7 @@ static int __reserve_bp_slot(struct perf_event *bp, u64 bp_type) 
	struct bp_busy_slots slots = {0};

	enum bp_type_idx type;

	int weight;

	int ret;



	/* We couldn't initialize breakpoint constraints on boot */

	if (!constraints_initialized)
@@ -294,6 +304,10 @@ static int __reserve_bp_slot(struct perf_event *bp, u64 bp_type) 
	if (slots.pinned + (!!slots.flexible) > nr_slots[type])

		return -ENOSPC;



	ret = arch_reserve_bp_slot(bp);

	if (ret)

		return ret;



	toggle_bp_slot(bp, true, type, weight);



	return 0;
@@ -317,6 +331,8 @@ static void __release_bp_slot(struct perf_event *bp, u64 bp_type) 
	enum bp_type_idx type;

	int weight;



	arch_release_bp_slot(bp);



	type = find_slot_idx(bp_type);

	weight = hw_breakpoint_weight(bp);

	toggle_bp_slot(bp, false, type, weight);