Re: [PATCH v6 2/6] arm64: ptrace: allow tracer to skip a system call

[AKASHI Takahiro]

On 09/02/2014 06:16 PM, Russell King - ARM Linux wrote:
> On Tue, Sep 02, 2014 at 05:47:29PM +0900, AKASHI Takahiro wrote:
> > On 09/01/2014 08:47 PM, Russell King - ARM Linux wrote:
> > > On Wed, Aug 27, 2014 at 02:55:46PM +0900, AKASHI Takahiro wrote:
> > > > 1)
> > > > setting x0 to -ENOSYS is necessary because, otherwise, user-issued syscall(-1) will
> > > > return a bogus value when audit tracing is on.
> > > >
> > > > Please note that, on arm,
> > > >                    not traced      traced
> > > >                    ------          ------
> > > > syscall(-1)      aborted         OOPs(BUG_ON)
> > > > syscall(-3000)   aborted         aborted
> > > > syscall(1000)    ENOSYS          ENOSYS
> > >
> > > Two points here:
> > >
> > > 1. You've found a case which causes a BUG_ON().  Where is the bug report
> > >      for this, so the problem can be investigated and resolved?
> >
> > I think that I mentioned it could also happen on arm somewhere in a talk
> > with Will, but don't remember exactly when.
>
> Sorry, not good enough.  Please report this bug so it can be investigated
> and fixed.

Please review my patch as well as the commit message.

> > > 2. What do you mean by "aborted" ?
> >
> > I mean that the process will receive SIGILL and get aborted.
> > A system call number, like -1 and -3000, won't be trapped by *switch*
> > statement in asm_syscall() and end up with being signaled.
>
> That is correct behaviour - because numbers greater than 0xf0000 (or
> 0x9f0000 for OABI - the 0x900000 offset on the syscalls on OABI is to
> distinguish them from syscalls used by RISC OS) are not intended to
> be Linux syscalls per-se.

I tried to make such invalid/pseudo syscalls hehave in the same way
whether or not a task is traced (by seccomp, ptrace or audit).

> > > Please, if you find a problem with 32-bit ARM, report it.  Don't hide it,
> > > because hiding it can be a security issue or in the case of BUG_ON(), it
> > > could be a denial of service issue.
> > >
> > > As you're part of Linaro, I would have thought you'd be more responsible
> > > in this regard - after all, Linaro is supposed to be about improving the
> > > ARM kernel...  Maybe I got that wrong, and Linaro is actually about
> > > ensuring that the ARM kernel is stuffed full of broken features?
> >
> > I thought my first priority was on arm64 (and then arm), but now that
> > you and Will seem to want to see the fix first on arm, okey, I will
> > start with arm issue.
>
> So what you're saying there is that if you find a bug in ARM code, which
> everyone is currently using, you can ignore it until you've sorted out
> ARM64 which almost no one is using.
>
> This is absurd, and whoever has set your priorities is clearly on drugs.

Thank you. I learned a new English word, absurd.

-Takahiro AKASHI

>


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/