linux-kernel - Re: [RFC,PATCH 0/14] utrace/ptrace

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Date:	Wed, 25 Nov 2009 16:40:52 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Ananth N Mavinakayanahalli <ananth@...ibm.com>
Cc:	Alexey Dobriyan <adobriyan@...il.com>,
	Christoph Hellwig <hch@...radead.org>,
	"Frank Ch. Eigler" <fche@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	Roland McGrath <roland@...hat.com>,
	linux-kernel@...r.kernel.org, utrace-devel@...hat.com
Subject: Re: [RFC,PATCH 0/14] utrace/ptrace

On 11/25, Ananth N Mavinakayanahalli wrote:
>
> I ran the ptrace-tests testsuite [1] on powerpc on the vanilla ptrace
> and then with ptrace/utrace. The results for ptrace/utrace look better
> :-)

Great! thanks a lot Ananth for doing this.

ptrace-utrace still fails 2 tests,

> FAIL: syscall-reset

I'll take a look later. Since unpatched kernel fails this test too
I am not going to worry right now. I think this is ppc specific, x86
passes this test.

> step-fork: step-fork.c:56: handler_fail: Assertion `0' failed.
> /bin/sh: line 5: 24803 Aborted                 ${dir}$tst
> FAIL: step-fork

This is expected. Should be fixed by

	ptrace-copy_process-should-disable-stepping.patch

in -mm tree. (I am attaching this patch below just in case)
I din't mention this patch in this series because this bug
is "ortogonal" to utrace/ptrace.

Oleg.

------------------------------------------------------
If the tracee calls fork() after PTRACE_SINGLESTEP, the forked child
starts with TIF_SINGLESTEP/X86_EFLAGS_TF bits copied from ptraced parent.
This is not right, especially when the new child is not auto-attaced: in
this case it is killed by SIGTRAP.

Change copy_process() to call user_disable_single_step(). Tested on x86.

Test-case:

	#include <stdio.h>
	#include <unistd.h>
	#include <signal.h>
	#include <sys/ptrace.h>
	#include <sys/wait.h>
	#include <assert.h>

	int main(void)
	{
		int pid, status;

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

			if (!fork()) {
				/* kernel bug: this child will be killed by SIGTRAP */
				printf("Hello world\n");
				return 43;
			}

			wait(&status);
			return WEXITSTATUS(status);
		}

		for (;;) {
			assert(pid == wait(&status));
			if (WIFEXITED(status))
				break;
			assert(ptrace(PTRACE_SINGLESTEP, pid, 0,0) == 0);
		}

		assert(WEXITSTATUS(status) == 43);
		return 0;
	}

Signed-off-by: Oleg Nesterov <oleg@...hat.com>
Acked-by: Roland McGrath <roland@...hat.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
---


diff -puN kernel/fork.c~ptrace-copy_process-should-disable-stepping kernel/fork.c
--- a/kernel/fork.c~ptrace-copy_process-should-disable-stepping
+++ a/kernel/fork.c
@@ -1203,9 +1203,10 @@ static struct task_struct *copy_process(
 		p->sas_ss_sp = p->sas_ss_size = 0;
 
 	/*
-	 * Syscall tracing should be turned off in the child regardless
-	 * of CLONE_PTRACE.
+	 * Syscall tracing and stepping should be turned off in the
+	 * child regardless of CLONE_PTRACE.
 	 */
+	user_disable_single_step(p);
 	clear_tsk_thread_flag(p, TIF_SYSCALL_TRACE);
 #ifdef TIF_SYSCALL_EMU
 	clear_tsk_thread_flag(p, TIF_SYSCALL_EMU);

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