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Date:      Tue, 20 May 2014 09:19:35 +0000 (UTC)
From:      Konstantin Belousov <kib@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org
Subject:   svn commit: r266464 - in head/sys: kern sys vm
Message-ID:  <201405200919.s4K9JZvg087765@svn.freebsd.org>
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Author: kib
Date: Tue May 20 09:19:35 2014
New Revision: 266464
URL: http://svnweb.freebsd.org/changeset/base/266464

Log:
  When exec_new_vmspace() decides that current vmspace cannot be reused
  on execve(2), it calls vmspace_exec(), which frees the current
  vmspace.  The thread executing an exec syscall gets new vmspace
  assigned, and old vmspace is freed if only referenced by the current
  process.  The free operation includes pmap_release(), which
  de-constructs the paging structures used by hardware.
  
  If the calling process is multithreaded, other threads are suspended
  in the thread_suspend_check(), and need to be unsuspended and run to
  be able to exit on successfull exec.  Now, since the old vmspace is
  destroyed, paging structures are invalid, threads are resumed on the
  non-existent pmaps (page tables), which leads to triple fault on x86.
  
  To fix, postpone the free of old vmspace until the threads are resumed
  and exited.  To avoid modifications to all image activators all of
  which use exec_new_vmspace(), memoize the current (old) vmspace in
  kern_execve(), and notify it about the need to call vmspace_free()
  with a thread-private flag TDP_EXECVMSPC.
  
  http://bugs.debian.org/743141
  
  Reported by:	Ivo De Decker <ivo.dedecker@ugent.be> through secteam
  Sponsored by:	The FreeBSD Foundation
  MFC after:	3 days

Modified:
  head/sys/kern/kern_exec.c
  head/sys/sys/proc.h
  head/sys/vm/vm_map.c

Modified: head/sys/kern/kern_exec.c
==============================================================================
--- head/sys/kern/kern_exec.c	Tue May 20 03:00:20 2014	(r266463)
+++ head/sys/kern/kern_exec.c	Tue May 20 09:19:35 2014	(r266464)
@@ -282,6 +282,7 @@ kern_execve(td, args, mac_p)
 	struct mac *mac_p;
 {
 	struct proc *p = td->td_proc;
+	struct vmspace *oldvmspace;
 	int error;
 
 	AUDIT_ARG_ARGV(args->begin_argv, args->argc,
@@ -298,6 +299,8 @@ kern_execve(td, args, mac_p)
 		PROC_UNLOCK(p);
 	}
 
+	KASSERT((td->td_pflags & TDP_EXECVMSPC) == 0, ("nested execve"));
+	oldvmspace = td->td_proc->p_vmspace;
 	error = do_execve(td, args, mac_p);
 
 	if (p->p_flag & P_HADTHREADS) {
@@ -312,6 +315,12 @@ kern_execve(td, args, mac_p)
 			thread_single_end();
 		PROC_UNLOCK(p);
 	}
+	if ((td->td_pflags & TDP_EXECVMSPC) != 0) {
+		KASSERT(td->td_proc->p_vmspace != oldvmspace,
+		    ("oldvmspace still used"));
+		vmspace_free(oldvmspace);
+		td->td_pflags &= ~TDP_EXECVMSPC;
+	}
 
 	return (error);
 }

Modified: head/sys/sys/proc.h
==============================================================================
--- head/sys/sys/proc.h	Tue May 20 03:00:20 2014	(r266463)
+++ head/sys/sys/proc.h	Tue May 20 09:19:35 2014	(r266464)
@@ -429,6 +429,7 @@ do {									\
 #define	TDP_NERRNO	0x08000000 /* Last errno is already in td_errno */
 #define	TDP_UIOHELD	0x10000000 /* Current uio has pages held in td_ma */
 #define	TDP_DEVMEMIO	0x20000000 /* Accessing memory for /dev/mem */
+#define	TDP_EXECVMSPC	0x40000000 /* Execve destroyed old vmspace */
 
 /*
  * Reasons that the current thread can not be run yet.

Modified: head/sys/vm/vm_map.c
==============================================================================
--- head/sys/vm/vm_map.c	Tue May 20 03:00:20 2014	(r266463)
+++ head/sys/vm/vm_map.c	Tue May 20 09:19:35 2014	(r266464)
@@ -3758,6 +3758,8 @@ vmspace_exec(struct proc *p, vm_offset_t
 	struct vmspace *oldvmspace = p->p_vmspace;
 	struct vmspace *newvmspace;
 
+	KASSERT((curthread->td_pflags & TDP_EXECVMSPC) == 0,
+	    ("vmspace_exec recursed"));
 	newvmspace = vmspace_alloc(minuser, maxuser, NULL);
 	if (newvmspace == NULL)
 		return (ENOMEM);
@@ -3774,7 +3776,7 @@ vmspace_exec(struct proc *p, vm_offset_t
 	PROC_VMSPACE_UNLOCK(p);
 	if (p == curthread->td_proc)
 		pmap_activate(curthread);
-	vmspace_free(oldvmspace);
+	curthread->td_pflags |= TDP_EXECVMSPC;
 	return (0);
 }

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