[uml-devel] Re: [patch] uml fixes, 2.6.1-mm5-A2

[Ingo Molnar <mingo@elte.hu>]

* Jeff Dike <jdike@addtoit.com> wrote:

> On Fri, Jan 23, 2004 at 10:35:41AM +0100, Ingo Molnar wrote:
> > hm, there's this code in arch/um/sys-i386/bugs.c:arch_handle_signal():
> > 
> >         ip = UPT_IP(regs);
> >         if((*((char *) ip) != 0x0f) || ((*((char *) (ip + 1)) & 0xf0) != 0x40))
> >                 return(0);
> > 
> > we are running in the UML kernel context here. Is the dereferencing of
> > IP safe? 
> 
> No, it's not.  There needs to be a copy_from_user in there.

ok - partial patch below. (Couldnt figure out how to include the proper
uaccess.h file to get copy_from_user() - so the build will fail with
this patch for the time being.)

	Ingo

--- linux/arch/um/sys-i386/bugs.c.orig	
+++ linux/arch/um/sys-i386/bugs.c	
@@ -183,15 +183,16 @@ void arch_check_bugs(void)
 
 int arch_handle_signal(int sig, union uml_pt_regs *regs)
 {
-	unsigned long ip;
+	unsigned char tmp[2];
 
 	/* This is testing for a cmov (0x0f 0x4x) instruction causing a
 	 * SIGILL in init.
 	 */
 	if((sig != SIGILL) || (TASK_PID(get_current()) != 1)) return(0);
 
-	ip = UPT_IP(regs);
-	if((*((char *) ip) != 0x0f) || ((*((char *) (ip + 1)) & 0xf0) != 0x40))
+	if (copy_from_user(tmp, UPT_IP(regs), 2))
+		panic("SIGILL in init, could not read instructions!\n");
+	if((tmp[0] != 0x0f) || ((tmp[1] & 0xf0) != 0x40))
 		return(0);
 
 	if(host_has_cmov == 0)


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