[uml-devel] Big SKAS3 bug found with 2.6/CONFIG_REGPARM - please upgrade

[Blaisorblade <blaisorblade@yahoo.it>]

I've worked during this weekend to diagnose the problem I reported earlier, in 
the thread " Please test 2.6.13-rc2 in TT mode! Big problem with syscall 
parameters clobbering".

It can affect an application when these conditions are verified:
*) the host is running a 2.6 kernel with SKAS patch and is compiled with 
CONFIG_REGPARM
*) it is calling sys_mmap2, old_mmap, sys_mprotect or sys_modify_ldt
*) the call happens via int 0x80
*) on return, the application relies on the values stored in registers 
(actually on some specific registers, depending on the exact situation).

Condition 3 means that a dynamically linked app with NPTL glibc won't incur in 
this problem, nor will statically linked app compiled on NPTL-only distros.

I've tested 2.6.9-V7, 2.6.11-V8/-V9-pre4 and 2.6.12-V8/-V9-pre4, all with 
CONFIG_REGPARM enabled, and compiled with gcc 3.3.4, and they all show this 
bug. Analysis with CONFIG_REGPARM disabled show that the problem won't happen.

Probably gcc 3.4 triggers it as well; the buggy code is present 
unchanged even in SKAS3-V1 against 2.6.3, although maybe it wouldn't be 
triggered by such an old kernel (because CONFIG_REGPARM wasn't present IIRC).

The solution, for user, is to upgrade to SKAS3-V8.2, or to SKAS3-v9-pre7 
(which is still to consider as *experimental*).
-- 
Inform me of my mistakes, so I can keep imitating Homer Simpson's "Doh!".
Paolo Giarrusso, aka Blaisorblade (Skype ID "PaoloGiarrusso", ICQ 215621894)
http://www.user-mode-linux.org/~blaisorblade


	

	
		
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