Re: [uml-devel] [PATCH] x86_64 32-bit ptrace mangles sixth system call argument

[Jeff Dike <jdike@addtoit.com>]

On Fri, Feb 02, 2007 at 06:48:39PM +0100, Blaisorblade wrote:
> Is this a recent regression or did this always happen?

I haven't looked at the history of the code, but it has the look of
something that's been there a long time.

> Is this the bug diagnosed by Bodo Stroesser time ago, or only it looks 
> similar? I recall vaguely that in that bug RCX was corrupted.

No, RCX corruption is different - that happens when a sysexit is done
from a system call where userspace wasn't prepared to save and restore
RCX.  sigreturn is the best example.

> Above all, how can UML run in SKAS0 mode with this bug (if it can)?

The impact is limited by several things -
	it must be a 32-bit UML on a 64-bit host
	the system call must have 6 arguments - mmap and pselect are
the only 6-argument system calls that I can find quickly
	the system call must be made through sysenter - int 0x80 is
fine

But, a 32-bit UML making mmap calls through sysenter indeed does not run
very well.

				Jeff

-- 
Work email - jdike at linux dot intel dot com

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