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

From: Oleg Nesterov
Date: Mon May 13 2013 - 11:21:49 EST


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 <oleg@xxxxxxxxxx>
Acked-by: Frederic Weisbecker <fweisbec@xxxxxxxxx>
---
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

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