From: Will Deacon <will.deacon@arm.com>
To: AKASHI Takahiro <takahiro.akashi@linaro.org>
Cc: Andy Lutomirski <luto@amacapital.net>,
Deepak Saxena <dsaxena@linaro.org>,
Will Drewry <wad@chromium.org>, Kees Cook <keescook@chromium.org>,
"linaro-kernel@lists.linaro.org" <linaro-kernel@lists.linaro.org>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>,
Catalin Marinas <Catalin.Marinas@arm.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v5 1/3] arm64: ptrace: reload a syscall number after ptrace operations
Date: Tue, 29 Jul 2014 14:26:59 +0100 [thread overview]
Message-ID: <20140729132659.GR9245@arm.com> (raw)
In-Reply-To: <53D7440B.10006@linaro.org>
On Tue, Jul 29, 2014 at 07:49:47AM +0100, AKASHI Takahiro wrote:
> On 07/25/2014 08:03 PM, Will Deacon wrote:
> > On Fri, Jul 25, 2014 at 11:36:49AM +0100, AKASHI Takahiro wrote:
> >> On 07/25/2014 12:01 AM, Andy Lutomirski wrote:
> >>>>> If so, then you risk (at least) introducing
> >>>>>
> >>>>> a nice user-triggerable OOPS if audit is enabled.
> >>>>
> >>>>
> >>>> Can you please elaborate this?
> >>>> Since I didn't find any definition of audit's behavior when syscall is
> >>>> rewritten to -1, I thought it is reasonable to skip "exit tracing" of
> >>>> "skipped" syscall.
> >>>> (otherwise, "fake" seems to be more appropriate :)
> >>>
> >>> The audit entry hook will oops if you call it twice in a row without
> >>> calling the exit hook in between.
> >>
> >> Thank you, I could reproduce this problem which hits BUG(in_syscall) in
> >> audit_syscall_entry(). Really bad, and I fixed it in my next version and
> >> now a "skipped" system call is also traced by audit.
> >
> > Can you reproduce this on arch/arm/ too? If so, we should also fix the code
> > there.
>
> As far as I tried on arm with syscall auditing enabled,
>
> 1) Changing a syscall number to -1 under seccomp doesn't hit BUG_ON(in_syscall).
> 2) But, in fact, audit_syscall_entry() is NOT called in this case because
> __secure_computing() returns -1 and then it causes the succeeding tracing
> in syscall_trace_enter(), including audit_syscall_entry(), skipped.
What happens if CONFIG_SECCOMP=n?
> 3) On the other hand, calling syscall(-1) from userspace hits BUG_ON because
> the return path, ret_slow_syscall, doesn't contain syscall_trace_exit().
> 4) When we re-write a syscall number to -1 without seccomp, we will also see
> BUG_ON hit, although I didn't try yet.
>
> Fixing case 3 is easy, but should we also fix case 2?
I think so.
Will
next prev parent reply other threads:[~2014-07-29 13:27 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-07-22 9:14 [PATCH v5 0/3] arm64: Add seccomp support AKASHI Takahiro
2014-07-22 9:14 ` [PATCH v5 1/3] arm64: ptrace: reload a syscall number after ptrace operations AKASHI Takahiro
2014-07-22 20:15 ` Kees Cook
2014-07-23 7:03 ` AKASHI Takahiro
2014-07-23 8:25 ` Will Deacon
2014-07-23 9:09 ` AKASHI Takahiro
2014-07-23 15:13 ` Kees Cook
2014-07-24 3:54 ` Andy Lutomirski
2014-07-24 5:57 ` AKASHI Takahiro
2014-07-24 15:01 ` Andy Lutomirski
2014-07-25 10:36 ` AKASHI Takahiro
2014-07-25 11:03 ` Will Deacon
2014-07-29 6:49 ` AKASHI Takahiro
2014-07-29 13:26 ` Will Deacon [this message]
2014-07-22 9:14 ` [PATCH v5 2/3] asm-generic: Add generic seccomp.h for secure computing mode 1 AKASHI Takahiro
2014-07-24 3:40 ` Andy Lutomirski
2014-07-24 4:41 ` Kees Cook
2014-07-24 5:17 ` AKASHI Takahiro
2014-07-24 14:57 ` Andy Lutomirski
2014-07-25 8:52 ` AKASHI Takahiro
2014-07-22 9:14 ` [PATCH v5 3/3] arm64: Add seccomp support AKASHI Takahiro
2014-07-24 3:52 ` Andy Lutomirski
2014-07-24 5:40 ` AKASHI Takahiro
2014-07-24 15:00 ` Andy Lutomirski
2014-07-24 15:16 ` Catalin Marinas
2014-07-25 9:37 ` AKASHI Takahiro
2014-08-05 15:08 ` Kees Cook
2014-08-08 7:35 ` AKASHI Takahiro
2014-08-11 9:24 ` Will Deacon
2014-08-12 6:57 ` AKASHI Takahiro
2014-08-12 9:40 ` Will Deacon
2014-08-12 11:17 ` AKASHI Takahiro
2014-08-15 14:33 ` Will Deacon
2014-07-22 20:16 ` [PATCH v5 0/3] " Kees Cook
2014-07-23 7:09 ` AKASHI Takahiro
2014-07-23 15:36 ` Kees Cook
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