Contributors: 2
Author Tokens Token Proportion Commits Commit Proportion
Benjamin Gray 1316 63.45% 2 66.67%
Ravi Bangoria 758 36.55% 1 33.33%
Total 2074 3 


// SPDX-License-Identifier: GPL-2.0+

#include <asm/unistd.h>
#include <linux/hw_breakpoint.h>
#include <linux/ptrace.h>
#include <memory.h>
#include <stdlib.h>
#include <sys/wait.h>

#include "utils.h"

/*
 * Child subroutine that performs a load on the address, then traps
 */
void same_watch_addr_child(unsigned long *addr);

/* Address of the ld instruction in same_watch_addr_child() */
extern char same_watch_addr_load[];

/* Address of the end trap instruction in same_watch_addr_child() */
extern char same_watch_addr_trap[];

/*
 * Child subroutine that performs a load on the first address, then a load on
 * the second address (with no instructions separating this from the first
 * load), then traps.
 */
void perf_then_ptrace_child(unsigned long *first_addr, unsigned long *second_addr);

/* Address of the first ld instruction in perf_then_ptrace_child() */
extern char perf_then_ptrace_load1[];

/* Address of the second ld instruction in perf_then_ptrace_child() */
extern char perf_then_ptrace_load2[];

/* Address of the end trap instruction in perf_then_ptrace_child() */
extern char perf_then_ptrace_trap[];

static inline long sys_ptrace(long request, pid_t pid, unsigned long addr, unsigned long data)
{
	return syscall(__NR_ptrace, request, pid, addr, data);
}

static long ptrace_traceme(void)
{
	return sys_ptrace(PTRACE_TRACEME, 0, 0, 0);
}

static long ptrace_getregs(pid_t pid, struct pt_regs *result)
{
	return sys_ptrace(PTRACE_GETREGS, pid, 0, (unsigned long)result);
}

static long ptrace_setregs(pid_t pid, struct pt_regs *result)
{
	return sys_ptrace(PTRACE_SETREGS, pid, 0, (unsigned long)result);
}

static long ptrace_cont(pid_t pid, long signal)
{
	return sys_ptrace(PTRACE_CONT, pid, 0, signal);
}

static long ptrace_singlestep(pid_t pid, long signal)
{
	return sys_ptrace(PTRACE_SINGLESTEP, pid, 0, signal);
}

static long ppc_ptrace_gethwdbginfo(pid_t pid, struct ppc_debug_info *dbginfo)
{
	return sys_ptrace(PPC_PTRACE_GETHWDBGINFO, pid, 0, (unsigned long)dbginfo);
}

static long ppc_ptrace_sethwdbg(pid_t pid, struct ppc_hw_breakpoint *bp_info)
{
	return sys_ptrace(PPC_PTRACE_SETHWDEBUG, pid, 0, (unsigned long)bp_info);
}

static long ppc_ptrace_delhwdbg(pid_t pid, int bp_id)
{
	return sys_ptrace(PPC_PTRACE_DELHWDEBUG, pid, 0L, bp_id);
}

static long ptrace_getreg_pc(pid_t pid, void **pc)
{
	struct pt_regs regs;
	long err;

	err = ptrace_getregs(pid, &regs);
	if (err)
		return err;

	*pc = (void *)regs.nip;

	return 0;
}

static long ptrace_setreg_pc(pid_t pid, void *pc)
{
	struct pt_regs regs;
	long err;

	err = ptrace_getregs(pid, &regs);
	if (err)
		return err;

	regs.nip = (unsigned long)pc;

	err = ptrace_setregs(pid, &regs);
	if (err)
		return err;

	return 0;
}

static int perf_event_open(struct perf_event_attr *attr, pid_t pid, int cpu,
			   int group_fd, unsigned long flags)
{
	return syscall(__NR_perf_event_open, attr, pid, cpu, group_fd, flags);
}

static void perf_user_event_attr_set(struct perf_event_attr *attr, void *addr, u64 len)
{
	memset(attr, 0, sizeof(struct perf_event_attr));

	attr->type		= PERF_TYPE_BREAKPOINT;
	attr->size		= sizeof(struct perf_event_attr);
	attr->bp_type		= HW_BREAKPOINT_R;
	attr->bp_addr		= (u64)addr;
	attr->bp_len		= len;
	attr->exclude_kernel	= 1;
	attr->exclude_hv	= 1;
}

static int perf_watchpoint_open(pid_t child_pid, void *addr, u64 len)
{
	struct perf_event_attr attr;

	perf_user_event_attr_set(&attr, addr, len);
	return perf_event_open(&attr, child_pid, -1, -1, 0);
}

static int perf_read_counter(int perf_fd, u64 *count)
{
	/*
	 * A perf counter is retrieved by the read() syscall. It contains
	 * the current count as 8 bytes that are interpreted as a u64
	 */
	ssize_t len = read(perf_fd, count, sizeof(*count));

	if (len != sizeof(*count))
		return -1;

	return 0;
}

static void ppc_ptrace_init_breakpoint(struct ppc_hw_breakpoint *info,
				       int type, void *addr, int len)
{
	info->version = 1;
	info->trigger_type = type;
	info->condition_mode = PPC_BREAKPOINT_CONDITION_NONE;
	info->addr = (u64)addr;
	info->addr2 = (u64)addr + len;
	info->condition_value = 0;
	if (!len)
		info->addr_mode = PPC_BREAKPOINT_MODE_EXACT;
	else
		info->addr_mode = PPC_BREAKPOINT_MODE_RANGE_INCLUSIVE;
}

/*
 * Checks if we can place at least 2 watchpoints on the child process
 */
static int check_watchpoints(pid_t pid)
{
	struct ppc_debug_info dbginfo;

	FAIL_IF_MSG(ppc_ptrace_gethwdbginfo(pid, &dbginfo), "PPC_PTRACE_GETHWDBGINFO failed");
	SKIP_IF_MSG(dbginfo.num_data_bps <= 1, "Not enough data watchpoints (need at least 2)");

	return 0;
}

/*
 * Wrapper around a plain fork() call that sets up the child for
 * ptrace-ing. Both the parent and child return from this, though
 * the child is stopped until ptrace_cont(pid) is run by the parent.
 */
static int ptrace_fork_child(pid_t *pid)
{
	int status;

	*pid = fork();

	if (*pid < 0)
		FAIL_IF_MSG(1, "Failed to fork child");

	if (!*pid) {
		FAIL_IF_EXIT_MSG(ptrace_traceme(), "PTRACE_TRACEME failed");
		FAIL_IF_EXIT_MSG(raise(SIGSTOP), "Child failed to raise SIGSTOP");
	} else {
		/* Synchronise on child SIGSTOP */
		FAIL_IF_MSG(waitpid(*pid, &status, 0) == -1, "Failed to wait for child");
		FAIL_IF_MSG(!WIFSTOPPED(status), "Child is not stopped");
	}

	return 0;
}

/*
 * Tests the interaction between ptrace and perf watching the same data.
 *
 * We expect ptrace to take 'priority', as it is has before-execute
 * semantics.
 *
 * The perf counter should not be incremented yet because perf has after-execute
 * semantics. E.g., if ptrace changes the child PC, we don't even execute the
 * instruction at all.
 *
 * When the child is stopped for ptrace, we test both continue and single step.
 * Both should increment the perf counter. We also test changing the PC somewhere
 * different and stepping, which should not increment the perf counter.
 */
int same_watch_addr_test(void)
{
	struct ppc_hw_breakpoint bp_info;	/* ptrace breakpoint info */
	int bp_id;	/* Breakpoint handle of ptrace watchpoint */
	int perf_fd;	/* File descriptor of perf performance counter */
	u64 perf_count;	/* Most recently fetched perf performance counter value */
	pid_t pid;	/* PID of child process */
	void *pc;	/* Most recently fetched child PC value */
	int status;	/* Stop status of child after waitpid */
	unsigned long value;	/* Dummy value to be read/written to by child */
	int err;

	err = ptrace_fork_child(&pid);
	if (err)
		return err;

	if (!pid) {
		same_watch_addr_child(&value);
		exit(1);
	}

	err = check_watchpoints(pid);
	if (err)
		return err;

	/* Place a perf watchpoint counter on value */
	perf_fd = perf_watchpoint_open(pid, &value, sizeof(value));
	FAIL_IF_MSG(perf_fd < 0, "Failed to open perf performance counter");

	/* Place a ptrace watchpoint on value */
	ppc_ptrace_init_breakpoint(&bp_info, PPC_BREAKPOINT_TRIGGER_READ, &value, sizeof(value));
	bp_id = ppc_ptrace_sethwdbg(pid, &bp_info);
	FAIL_IF_MSG(bp_id < 0, "Failed to set ptrace watchpoint");

	/* Let the child run. It should stop on the ptrace watchpoint */
	FAIL_IF_MSG(ptrace_cont(pid, 0), "Failed to continue child");

	FAIL_IF_MSG(waitpid(pid, &status, 0) == -1, "Failed to wait for child");
	FAIL_IF_MSG(!WIFSTOPPED(status), "Child is not stopped");
	FAIL_IF_MSG(ptrace_getreg_pc(pid, &pc), "Failed to get child PC");
	FAIL_IF_MSG(pc != same_watch_addr_load, "Child did not stop on load instruction");

	/*
	 * We stopped before executing the load, so perf should not have
	 * recorded any events yet
	 */
	FAIL_IF_MSG(perf_read_counter(perf_fd, &perf_count), "Failed to read perf counter");
	FAIL_IF_MSG(perf_count != 0, "perf recorded unexpected event");

	/* Single stepping over the load should increment the perf counter */
	FAIL_IF_MSG(ptrace_singlestep(pid, 0), "Failed to single step child");

	FAIL_IF_MSG(waitpid(pid, &status, 0) == -1, "Failed to wait for child");
	FAIL_IF_MSG(!WIFSTOPPED(status), "Child is not stopped");
	FAIL_IF_MSG(ptrace_getreg_pc(pid, &pc), "Failed to get child PC");
	FAIL_IF_MSG(pc != same_watch_addr_load + 4, "Failed to single step load instruction");
	FAIL_IF_MSG(perf_read_counter(perf_fd, &perf_count), "Failed to read perf counter");
	FAIL_IF_MSG(perf_count != 1, "perf counter did not increment");

	/*
	 * Set up a ptrace watchpoint on the value again and trigger it.
	 * The perf counter should not have incremented because we do not
	 * execute the load yet.
	 */
	FAIL_IF_MSG(ppc_ptrace_delhwdbg(pid, bp_id), "Failed to remove old ptrace watchpoint");
	bp_id = ppc_ptrace_sethwdbg(pid, &bp_info);
	FAIL_IF_MSG(bp_id < 0, "Failed to set ptrace watchpoint");
	FAIL_IF_MSG(ptrace_setreg_pc(pid, same_watch_addr_load), "Failed to set child PC");
	FAIL_IF_MSG(ptrace_cont(pid, 0), "Failed to continue child");

	FAIL_IF_MSG(waitpid(pid, &status, 0) == -1, "Failed to wait for child");
	FAIL_IF_MSG(!WIFSTOPPED(status), "Child is not stopped");
	FAIL_IF_MSG(ptrace_getreg_pc(pid, &pc), "Failed to get child PC");
	FAIL_IF_MSG(pc != same_watch_addr_load, "Child did not stop on load trap");
	FAIL_IF_MSG(perf_read_counter(perf_fd, &perf_count), "Failed to read perf counter");
	FAIL_IF_MSG(perf_count != 1, "perf counter should not have changed");

	/* Continuing over the load should increment the perf counter */
	FAIL_IF_MSG(ptrace_cont(pid, 0), "Failed to continue child");

	FAIL_IF_MSG(waitpid(pid, &status, 0) == -1, "Failed to wait for child");
	FAIL_IF_MSG(!WIFSTOPPED(status), "Child is not stopped");
	FAIL_IF_MSG(ptrace_getreg_pc(pid, &pc), "Failed to get child PC");
	FAIL_IF_MSG(pc != same_watch_addr_trap, "Child did not stop on end trap");
	FAIL_IF_MSG(perf_read_counter(perf_fd, &perf_count), "Failed to read perf counter");
	FAIL_IF_MSG(perf_count != 2, "perf counter did not increment");

	/*
	 * If we set the child PC back to the load instruction, then continue,
	 * we should reach the end trap (because ptrace is one-shot) and have
	 * another perf event.
	 */
	FAIL_IF_MSG(ptrace_setreg_pc(pid, same_watch_addr_load), "Failed to set child PC");
	FAIL_IF_MSG(ptrace_cont(pid, 0), "Failed to continue child");

	FAIL_IF_MSG(waitpid(pid, &status, 0) == -1, "Failed to wait for child");
	FAIL_IF_MSG(!WIFSTOPPED(status), "Child is not stopped");
	FAIL_IF_MSG(ptrace_getreg_pc(pid, &pc), "Failed to get child PC");
	FAIL_IF_MSG(pc != same_watch_addr_trap, "Child did not stop on end trap");
	FAIL_IF_MSG(perf_read_counter(perf_fd, &perf_count), "Failed to read perf counter");
	FAIL_IF_MSG(perf_count != 3, "perf counter did not increment");

	/*
	 * If we set the child PC back to the load instruction, set a ptrace
	 * watchpoint on the load, then continue, we should immediately get
	 * the ptrace trap without incrementing the perf counter
	 */
	FAIL_IF_MSG(ppc_ptrace_delhwdbg(pid, bp_id), "Failed to remove old ptrace watchpoint");
	bp_id = ppc_ptrace_sethwdbg(pid, &bp_info);
	FAIL_IF_MSG(bp_id < 0, "Failed to set ptrace watchpoint");
	FAIL_IF_MSG(ptrace_setreg_pc(pid, same_watch_addr_load), "Failed to set child PC");
	FAIL_IF_MSG(ptrace_cont(pid, 0), "Failed to continue child");

	FAIL_IF_MSG(waitpid(pid, &status, 0) == -1, "Failed to wait for child");
	FAIL_IF_MSG(!WIFSTOPPED(status), "Child is not stopped");
	FAIL_IF_MSG(ptrace_getreg_pc(pid, &pc), "Failed to get child PC");
	FAIL_IF_MSG(pc != same_watch_addr_load, "Child did not stop on load instruction");
	FAIL_IF_MSG(perf_read_counter(perf_fd, &perf_count), "Failed to read perf counter");
	FAIL_IF_MSG(perf_count != 3, "perf counter should not have changed");

	/*
	 * If we change the PC while stopped on the load instruction, we should
	 * not increment the perf counter (because ptrace is before-execute,
	 * perf is after-execute).
	 */
	FAIL_IF_MSG(ptrace_setreg_pc(pid, same_watch_addr_load + 4), "Failed to set child PC");
	FAIL_IF_MSG(ptrace_cont(pid, 0), "Failed to continue child");

	FAIL_IF_MSG(waitpid(pid, &status, 0) == -1, "Failed to wait for child");
	FAIL_IF_MSG(!WIFSTOPPED(status), "Child is not stopped");
	FAIL_IF_MSG(ptrace_getreg_pc(pid, &pc), "Failed to get child PC");
	FAIL_IF_MSG(pc != same_watch_addr_trap, "Child did not stop on end trap");
	FAIL_IF_MSG(perf_read_counter(perf_fd, &perf_count), "Failed to read perf counter");
	FAIL_IF_MSG(perf_count != 3, "perf counter should not have changed");

	/* Clean up child */
	FAIL_IF_MSG(kill(pid, SIGKILL) != 0, "Failed to kill child");

	return 0;
}

/*
 * Tests the interaction between ptrace and perf when:
 * 1. perf watches a value
 * 2. ptrace watches a different value
 * 3. The perf value is read, then the ptrace value is read immediately after
 *
 * A breakpoint implementation may accidentally misattribute/skip one of
 * the ptrace or perf handlers, as interrupt based work is done after perf
 * and before ptrace.
 *
 * We expect the perf counter to increment before the ptrace watchpoint
 * triggers.
 */
int perf_then_ptrace_test(void)
{
	struct ppc_hw_breakpoint bp_info;	/* ptrace breakpoint info */
	int bp_id;	/* Breakpoint handle of ptrace watchpoint */
	int perf_fd;	/* File descriptor of perf performance counter */
	u64 perf_count;	/* Most recently fetched perf performance counter value */
	pid_t pid;	/* PID of child process */
	void *pc;	/* Most recently fetched child PC value */
	int status;	/* Stop status of child after waitpid */
	unsigned long perf_value;	/* Dummy value to be watched by perf */
	unsigned long ptrace_value;	/* Dummy value to be watched by ptrace */
	int err;

	err = ptrace_fork_child(&pid);
	if (err)
		return err;

	/*
	 * If we are the child, run a subroutine that reads the perf value,
	 * then reads the ptrace value with consecutive load instructions
	 */
	if (!pid) {
		perf_then_ptrace_child(&perf_value, &ptrace_value);
		exit(0);
	}

	err = check_watchpoints(pid);
	if (err)
		return err;

	/* Place a perf watchpoint counter */
	perf_fd = perf_watchpoint_open(pid, &perf_value, sizeof(perf_value));
	FAIL_IF_MSG(perf_fd < 0, "Failed to open perf performance counter");

	/* Place a ptrace watchpoint */
	ppc_ptrace_init_breakpoint(&bp_info, PPC_BREAKPOINT_TRIGGER_READ,
				   &ptrace_value, sizeof(ptrace_value));
	bp_id = ppc_ptrace_sethwdbg(pid, &bp_info);
	FAIL_IF_MSG(bp_id < 0, "Failed to set ptrace watchpoint");

	/* Let the child run. It should stop on the ptrace watchpoint */
	FAIL_IF_MSG(ptrace_cont(pid, 0), "Failed to continue child");

	FAIL_IF_MSG(waitpid(pid, &status, 0) == -1, "Failed to wait for child");
	FAIL_IF_MSG(!WIFSTOPPED(status), "Child is not stopped");
	FAIL_IF_MSG(ptrace_getreg_pc(pid, &pc), "Failed to get child PC");
	FAIL_IF_MSG(pc != perf_then_ptrace_load2, "Child did not stop on ptrace load");

	/* perf should have recorded the first load */
	FAIL_IF_MSG(perf_read_counter(perf_fd, &perf_count), "Failed to read perf counter");
	FAIL_IF_MSG(perf_count != 1, "perf counter did not increment");

	/* Clean up child */
	FAIL_IF_MSG(kill(pid, SIGKILL) != 0, "Failed to kill child");

	return 0;
}

int main(int argc, char *argv[])
{
	int err = 0;

	err |= test_harness(same_watch_addr_test, "same_watch_addr");
	err |= test_harness(perf_then_ptrace_test, "perf_then_ptrace");

	return err;
}