Re: [uml-devel] Patch for arch/um/kernel/trap_kern.c to fix bad panic

[BlaisorBlade <blaisorblade_spam@yahoo.it>]

Alle 13:39, lunedì 28 giugno 2004, azu ha scritto:
> Hi,

> I triggered the following panic from userspace in skas mode
> by mapping pages above 0xa0000000 ...

> The check is useless in skas-mode (kernel faults get filtered
> in segv() before handle_page_fault() is called),
> so I added an ifdef for tt mode.

This is a more sensible version of the patch (with runtime checking instead 
that compile time), if I did not overlook anything: it must be an if(mode_tt). 
I always compile in TT mode and normally don't use it (and sometimes UML does 
not compile otherwise), and the patch must still work.


However, I don't think this is the proper fix: please elaborate a bit more. 
Segv() works the same way under TT and SKAS, and I think that more likely 
there were an actual stack overflow (try to increase 
CONFIG_KERNEL_STACK_ORDER and try to re-get the panic).

diff -puN arch/um/kernel/trap_kern.c~silly_panic arch/um/kernel/trap_kern.c
--- uml-linux-2.6.7/arch/um/kernel/trap_kern.c~silly_panic	2004-06-28 
21:42:06.025387464 +0200
+++ uml-linux-2.6.7-paolo/arch/um/kernel/trap_kern.c	2004-06-28 
21:43:47.676934080 +0200
@@ -54,8 +54,10 @@ int handle_page_fault(unsigned long addr
 	if(is_write && !(vma->vm_flags & VM_WRITE)) 
 		goto out;
 	page = address & PAGE_MASK;
-	if(page == (unsigned long) current_thread + PAGE_SIZE)
-		panic("Kernel stack overflow");
+	if (mode_tt) {
+		if(page == (unsigned long) current_thread + PAGE_SIZE)
+			panic("Kernel stack overflow");
+	}
 	pgd = pgd_offset(mm, page);
 	pmd = pmd_offset(pgd, page);
 	do {

-- 
Paolo Giarrusso, aka Blaisorblade
Linux registered user n. 292729



-------------------------------------------------------
This SF.Net email sponsored by Black Hat Briefings & Training.
Attend Black Hat Briefings & Training, Las Vegas July 24-29 - 
digital self defense, top technical experts, no vendor pitches, 
unmatched networking opportunities. Visit www.blackhat.com
_______________________________________________
User-mode-linux-devel mailing list
User-mode-linux-devel@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/user-mode-linux-devel