Messages in this thread Patch in this message | | | From | Tejun Heo <> | Subject | [PATCH 04/10] ptrace: implement PTRACE_INTERRUPT | Date | Mon, 16 May 2011 20:17:23 +0200 |
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Currently, there's no way to trap a running ptracee short of sending a signal which has various side effects. This patch implements PTRACE_INTERRUPT which traps ptracee without any signal or job control related side effect.
The implementation is almost trivial. It uses the group stop trap - SIGTRAP | PTRACE_EVENT_STOP << 8. A new trap flag JOBCTL_TRAP_INTERRUPT is added, which is set on PTRACE_INTERRUPT and cleared when any trap happens. As INTERRUPT should be useable regardless of the current state of tracee, task_is_traced() test in ptrace_check_attach() is skipped for INTERRUPT.
PTRACE_INTERRUPT is available iff tracee is attached with PTRACE_SEIZE.
Test program follows.
#define PTRACE_SEIZE 0x4206 #define PTRACE_INTERRUPT 0x4207
#define PTRACE_SEIZE_DEVEL 0x80000000
static const struct timespec ts100ms = { .tv_nsec = 100000000 }; static const struct timespec ts1s = { .tv_sec = 1 }; static const struct timespec ts3s = { .tv_sec = 3 };
int main(int argc, char **argv) { pid_t tracee;
tracee = fork(); if (tracee == 0) { nanosleep(&ts100ms, NULL); while (1) { printf("tracee: alive pid=%d\n", getpid()); nanosleep(&ts1s, NULL); } }
if (argc > 1) kill(tracee, SIGSTOP);
nanosleep(&ts100ms, NULL);
ptrace(PTRACE_SEIZE, tracee, NULL, (void *)(unsigned long)PTRACE_SEIZE_DEVEL); waitid(P_PID, tracee, NULL, WSTOPPED); ptrace(PTRACE_CONT, tracee, NULL, NULL); nanosleep(&ts3s, NULL);
printf("tracer: INTERRUPT and DETACH\n"); ptrace(PTRACE_INTERRUPT, tracee, NULL, NULL); waitid(P_PID, tracee, NULL, WSTOPPED); ptrace(PTRACE_DETACH, tracee, NULL, NULL); nanosleep(&ts3s, NULL);
printf("tracer: exiting\n"); kill(tracee, SIGKILL); return 0; }
When called without argument, tracee is seized from running state, continued, interrupted and then detached back to running state.
# ./test-interrupt tracee: alive pid=4546 tracee: alive pid=4546 tracee: alive pid=4546 tracer: INTERRUPT and DETACH tracee: alive pid=4546 tracee: alive pid=4546 tracee: alive pid=4546 tracer: exiting
When called with argument, it's the same but tracee is detached back to stopped state.
# ./test-interrupt 1 tracee: alive pid=4548 tracee: alive pid=4548 tracee: alive pid=4548 tracer: INTERRUPT and DETACH tracer: exiting
Before PTRACE_INTERRUPT, once the tracee was continued, there was no easy way to do PTRACE_DETACH without causing side effect as tracee couldn't be trapped without side effect.
Signed-off-by: Tejun Heo <tj@kernel.org> --- include/linux/ptrace.h | 1 + kernel/ptrace.c | 27 +++++++++++++++++++++++++-- 2 files changed, 26 insertions(+), 2 deletions(-)
diff --git a/include/linux/ptrace.h b/include/linux/ptrace.h index 3fd389d..b07b9e3 100644 --- a/include/linux/ptrace.h +++ b/include/linux/ptrace.h @@ -48,6 +48,7 @@ #define PTRACE_SETREGSET 0x4205 #define PTRACE_SEIZE 0x4206 +#define PTRACE_INTERRUPT 0x4207 /* flags in @data for PTRACE_SEIZE */ #define PTRACE_SEIZE_DEVEL 0x80000000 /* temp flag for development */ diff --git a/kernel/ptrace.c b/kernel/ptrace.c index 7aefd43..351db7c 100644 --- a/kernel/ptrace.c +++ b/kernel/ptrace.c @@ -706,6 +706,7 @@ int ptrace_request(struct task_struct *child, long request, siginfo_t siginfo; void __user *datavp = (void __user *) data; unsigned long __user *datalp = datavp; + unsigned long flags; switch (request) { case PTRACE_PEEKTEXT: @@ -738,6 +739,26 @@ int ptrace_request(struct task_struct *child, long request, ret = ptrace_setsiginfo(child, &siginfo); break; + case PTRACE_INTERRUPT: + /* + * Stop tracee without any side-effect on signal or job + * control. At least one trap is guaranteed to happen + * after this request. If @child is already trapped, the + * current trap is not disturbed and another trap will + * happen after the current trap is ended with PTRACE_CONT. + * + * The actual trap might not be PTRACE_EVENT_STOP trap but + * the pending condition is cleared regardless. + */ + if (likely(child->ptrace & PT_SEIZED) && + lock_task_sighand(child, &flags)) { + child->jobctl |= JOBCTL_TRAP_STOP; + signal_wake_up(child, 0); + unlock_task_sighand(child, &flags); + ret = 0; + } + break; + case PTRACE_DETACH: /* detach a process that was attached. */ ret = ptrace_detach(child, data); break; @@ -863,7 +884,8 @@ SYSCALL_DEFINE4(ptrace, long, request, long, pid, unsigned long, addr, goto out_put_task_struct; } - ret = ptrace_check_attach(child, request == PTRACE_KILL); + ret = ptrace_check_attach(child, request == PTRACE_KILL || + request == PTRACE_INTERRUPT); if (ret < 0) goto out_put_task_struct; @@ -1005,7 +1027,8 @@ asmlinkage long compat_sys_ptrace(compat_long_t request, compat_long_t pid, goto out_put_task_struct; } - ret = ptrace_check_attach(child, request == PTRACE_KILL); + ret = ptrace_check_attach(child, request == PTRACE_KILL || + request == PTRACE_INTERRUPT); if (!ret) ret = compat_arch_ptrace(child, request, addr, data); -- 1.7.1
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