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List:       freebsd-bugs
Subject:    kern/186236: sigcode not synced on executable stack on icache not coherent archs
From:       Svatopluk Kraus <onwahe () gmail ! com>
Date:       2014-01-29 14:03:25
Message-ID: 201401291403.s0TE3PVi032056 () oldred ! freebsd ! org
[Download RAW message or body]


> 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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