Re: [PATCH] audit: add arch field to seccomp event log

From: Richard Guy Briggs
Date: Wed Feb 19 2014 - 14:38:03 EST


On 14/02/18, Richard Guy Briggs wrote:
> On 14/02/18, Steve Grubb wrote:
> > On Tuesday, February 18, 2014 03:50:44 PM Richard Guy Briggs wrote:
> > > > missing '=' but this isn't what audit_get_context() does... it's
> > > > crappy naming... I'd think a combo of audit_dummy_context() and
> > > > current->audit_context would be most appropriate.
> > >
> > > Ok. I think I finally understand audit_dummy_context(). Thanks for the
> > > hint. However, it appears it is not useful in this sitation, since if
> > > there is an audit_context, even a dummy context, it appears arch is
> > > filled in.
> > >
> > > diff --git a/kernel/auditsc.c b/kernel/auditsc.c
> > > @@ -2406,12 +2406,18 @@ void audit_core_dumps(long signr)
> > > void __audit_seccomp(unsigned long syscall, long signr, int code)
> > > {
> > > struct audit_buffer *ab;
> > > + struct audit_context *context = current->audit_context;
> > >
> > > ab = audit_log_start(NULL, GFP_KERNEL, AUDIT_SECCOMP);
> > > if (unlikely(!ab))
> > > return;
> > > audit_log_task(ab);
> > > audit_log_format(ab, " sig=%ld", signr);
> > > + audit_log_format(ab, " arch=");
> > > + if (context)
> > > + audit_log_format(ab, "%x", context->arch);
> > > + else
> > > + audit_log_format(ab, "(null)");
> > > audit_log_format(ab, " syscall=%ld", syscall);
> > > audit_log_format(ab, " compat=%d", is_compat_task());
> > > audit_log_format(ab, " ip=0x%lx", KSTK_EIP(current));
> >
> > Is there anything that could be passed by the caller that might identify the
> > syscall ABI when this call was blocked? '(null)' still makes syscall number
> > uninterpretable.
>
> This is the way it is done in the existing record that prints a syscall
> record in audit_log_exit().
>
> It is set by the arch-dependent assembler linkage for
> __audit_syscall_entry() or set by the arch-dependent ptrace code that
> calls audit_syscall_entry(). In some arches there are a couple of
> choices.
>
>
> To pass this in to __audit_seccomp() as an arg, I'd have to add that arg
> to:
> __audit_seccomp()
> audit_seccomp()
> __secure_computing()
> secure_computing()
>
>
> As you've pointed out in IRC, there is a syscall_get_arch(current, regs)
> that could be used to get the arch when an audit context is not yet created.

s390x architecture doesn't have it defined. :(

> I was just looking for something like that... I am noticing that all
> arches call a variant of syscall_trace_enter() which first calls
> secure_computing() [which eventually calls __audit_seccomp()] *before*
> calling audit_syscall_entry() [which eventually sets context->arch]. So
> I'm not sure how task->audit_context->arch got set... Perhaps
> __audit_syscall_entry() should just call syscall_get_arch() instead of
> lugging it through the stack like it presently does.
>
> Is this going to give the same information? (I guess I should be able
> to answer that question...)
>
> > -Steve
>
> - RGB

- RGB

--
Richard Guy Briggs <rbriggs@xxxxxxxxxx>
Senior Software Engineer, Kernel Security, AMER ENG Base Operating Systems, Red Hat
Remote, Ottawa, Canada
Voice: +1.647.777.2635, Internal: (81) 32635, Alt: +1.613.693.0684x3545
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