[uml-devel] Cleanups about SYSEMU_SINGLESTEP / fixes about sysaudit-singlestep-umlhost

[Blaisorblade <bla...@ya...>]

Ok, the first thing is the cleanup of PTRACE_SYSEMU_SINGLESTEP. I've carefully 
moved the handling to go near to PTRACE_SINGLESTEP. As said, it's needed also 
to port this stuff to 2.6.10 easily (wrt the introduction of 
{clear,set}_singlestep).

The patch is attached both with only my changes, to go on top of the 
add-SYSEMU_SINGLESTEP one, and in the merged form. They are both for 2.6.9.

I'm also going to release both 2.6.9-V8-rc2 and 2.6.10-V8-rc2 with this stuff.

I also added a patch about mm->dumpable (still in doubt whether to merge it).

Second thing: I've analyzed sysaudit-singlestep-umlhost.... the important 
thing is #2 below.

1) there is some moving around of do_syscall_trace vars, which I've merged in 
my cleanup (it's needed for item #3, however it's nice anyway); so I've 
modified and reattached it.

2) I guess that the ptrace_disable() change (which clears TIF_SYSCALL_TRACE  
and TIF_SYSCALL_EMU) is just cosmetical.

I verified that in kernel/ and arch/i386/kernel the only caller is 
ptrace_detach (as the comment says), which later clears child->ptrace through 
__ptrace_unlink.

Since everything (I took this for granted) tests current->ptrace | PT_PTRACED, 
correctness should be ok.

It hurts a bit performance, however, because we don't run inside the syscall 
fastpath, and do one more conditional jump. We must discuss this with 
mainline, too.

3) a real fix for TIF_SYSCALL_AUDIT | TIF_SINGLESTEP, which is also correct 
when setting TIF_SYSCALL_EMU too (I had doubts about this, since I was 
missing that is_singlestep == 1 only for PTRACE_SINGLESTEP and not when doing 
PTRACE_SYSEMU_SINGLESTEP).

I want to merge it before 2.6.11.

We must in fact avoid to do the tracing for syscall entry, since 
TIF_SINGLESTEP does not trigger inside entry.S the syscall tracing (see the 
marked "testb" line below).

(around line 277 of arch/i386/kernel/entry.S):

ENTRY(system_call)
        pushl %eax                      # save orig_eax
        SAVE_ALL
        GET_THREAD_INFO(%ebp)
# system call tracing in operation / emulation


//in the mask _TIF_SINGLESTEP is not set !!! <<<<<<<<<<<<<<
        testb $(_TIF_SYSCALL_EMU|_TIF_SYSCALL_TRACE|
_TIF_SYSCALL_AUDIT),TI_flags(%ebp)


        jnz syscall_trace_entry
        cmpl $(nr_syscalls), %eax
        jae syscall_badsys
syscall_call:
        call *sys_call_table(,%eax,4)
        movl %eax,EAX(%esp)             # store the return value
syscall_exit:


-- 
Paolo Giarrusso, aka Blaisorblade
Linux registered user n. 292729
http://www.user-mode-linux.org/~blaisorblade