[PATCH 11/13] ptrace: PTRACE_DETACH should do flush_ptrace_hw_breakpoint(child)

[Oleg Nesterov]

Change ptrace_detach() to call flush_ptrace_hw_breakpoint(child).
This frees the slots for non-ptrace PERF_TYPE_BREAKPOINT users, and
this ensures that the tracee won't be killed by SIGTRAP triggered by
the active breakpoints.

Test-case:

        unsigned long encode_dr7(int drnum, int enable, unsigned int type, 
unsigned int len)
        {
                unsigned long dr7;

                dr7 = ((len | type) & 0xf)
                        << (DR_CONTROL_SHIFT + drnum * DR_CONTROL_SIZE);
                if (enable)
                        dr7 |= (DR_GLOBAL_ENABLE << (drnum * DR_ENABLE_SIZE));

                return dr7;
        }

        int write_dr(int pid, int dr, unsigned long val)
        {
                return ptrace(PTRACE_POKEUSER, pid,
                                offsetof (struct user, u_debugreg[dr]),
                                val);
        }

        void func(void)
        {
        }

        int main(void)
        {
                int pid, stat;
                unsigned long dr7;

                pid = fork();
                if (!pid) {
                        assert(ptrace(PTRACE_TRACEME, 0,0,0) == 0);
                        kill(getpid(), SIGHUP);

                        func();
                        return 0x13;
                }

                assert(pid == waitpid(-1, &stat, 0));
                assert(WSTOPSIG(stat) == SIGHUP);

                assert(write_dr(pid, 0, (long)func) == 0);
                dr7 = encode_dr7(0, 1, DR_RW_EXECUTE, DR_LEN_1);
                assert(write_dr(pid, 7, dr7) == 0);

                assert(ptrace(PTRACE_DETACH, pid, 0,0) == 0);
                assert(pid == waitpid(-1, &stat, 0));
                assert(stat == 0x1300);

                return 0;
        }

Before this patch the child is killed after PTRACE_DETACH.

Signed-off-by: Oleg Nesterov <o...@redhat.com>
Acked-by: Frederic Weisbecker <fweis...@gmail.com>
---
 kernel/ptrace.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index 8cc170b..0ea7f22 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -469,6 +469,7 @@ static int ptrace_detach(struct task_struct *child, 
unsigned int data)
        /* Architecture-specific hardware disable .. */
        ptrace_disable(child);
        clear_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
+       flush_ptrace_hw_breakpoint(child);
 
        write_lock_irq(&tasklist_lock);
        /*
-- 
1.5.5.1

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/