kern/186236: sigcode not synced on executable stack on icache not

>Number:         186236
>Category:       kern
>Synopsis:       sigcode not synced on executable stack on icache not coherent archs
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    freebsd-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Wed Jan 29 14:10:00 UTC 2014
>Closed-Date:
>Last-Modified:
>Originator:     Svatopluk Kraus
>Release:        current
>Organization:
>Environment:
>Description:
When sigcode (signal trampoline) is copied to user stack during exec, no icache syncing is called. This is problem on architectures where icache is not coherent.
>How-To-Repeat:
I have noticed the problem after fork(), when parent process was immediately sending signal to child process. As a cache problem, the problem displayed itself rarely.
>Fix:
I'm attaching simple patch. Another approche is to map user stack without exec privilege, copy sigcode, and then remap the stack with exec privilege.

Patch attached with submission follows:

Index: sys/kern/kern_exec.c
===================================================================
--- sys/kern/kern_exec.c	(revision 261262)
+++ sys/kern/kern_exec.c	(working copy)
@@ -1264,9 +1264,12 @@
 	/*
 	 * install sigcode
 	 */
-	if (szsigcode != 0)
+	if (szsigcode != 0) {
 		copyout(p->p_sysent->sv_sigcode, ((caddr_t)arginfo -
 		    szsigcode), szsigcode);
+		vm_sync_icache(&(p->p_vmspace->vm_map), ((vm_offset_t)arginfo -
+		    szsigcode), szsigcode);
+	}
 
 	/*
 	 * Copy the image path for the rtld.


>Release-Note:
>Audit-Trail:
>Unformatted:
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