Re: Bad code path in DoSyscall

On Mon, Nov 10, 2003 at 10:56:08AM -0500, John Whitney wrote:

There seems to be a bad code path in the assembly routine DoSyscall()
(arch/ppc/kernel/entry.S).  In the case of an invalid syscall being made (in
my case, from user space), DoSyscall is called and eventually branches to
label 66.  Note that before the branch, r12 is set to zero.

<snip>

    /* disable interrupts so current_thread_info()->flags can't change */
30: LOAD_MSR_KERNEL(r10,MSR_KERNEL) /* doesn't include MSR_EE */
    SYNC
    MTMSRD(r10)
    lwz r9,TI_FLAGS(r12)

Which immediately causes a bad page fault kernel oops.  I haven't come up
with a patch yet, but will try to when I get the time unless someone with
more knowledge in this area wants to do it.  Just wanted to let the list
know about the problem.

Thanks, here's a patch to grab the thread info when you go down the
no syscall path. This should cure the problem.

It's against linuxppc-2.5.  I think that's what you meant since this
bug isn't in 2.4.

-Matt

===== arch/ppc/kernel/entry.S 1.40 vs edited =====

--- 1.40/arch/ppc/kernel/entry.S        Sat Sep 27 03:58:48 2003
+++ edited/arch/ppc/kernel/entry.S      Mon Nov 10 09:36:55 2003

@@ -234,6 +234,7 @@
        RFI

 66:    li      r3,ENOSYS
+       rlwinm  r12,r1,0,0,18   /* current_thread_info() */
        b       22b

        .globl  ret_from_fork

** Sent via the linuxppc-dev mail list. See http://lists.linuxppc.org/