From: Will Deacon <will.deacon@arm.com>
To: AKASHI Takahiro <takahiro.akashi@linaro.org>
Cc: "linaro-kernel@lists.linaro.org" <linaro-kernel@lists.linaro.org>,
Will Drewry <wad@chromium.org>, Kees Cook <keescook@chromium.org>,
Catalin Marinas <Catalin.Marinas@arm.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Andy Lutomirski <luto@amacapital.net>,
Deepak Saxena <dsaxena@linaro.org>,
Lee Campbell <leecam@google.com>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH v5 3/3] arm64: Add seccomp support
Date: Tue, 12 Aug 2014 10:40:58 +0100 [thread overview]
Message-ID: <20140812094058.GD29013@arm.com> (raw)
In-Reply-To: <53E9BAD5.3080201@linaro.org>
Hi Akashi,
On Tue, Aug 12, 2014 at 07:57:25AM +0100, AKASHI Takahiro wrote:
> On 08/11/2014 06:24 PM, Will Deacon wrote:
> > On Fri, Aug 08, 2014 at 08:35:42AM +0100, AKASHI Takahiro wrote:
> >> As discussed in a few weeks ago, aarch64 won't support PTRACE_SET_SYSCALL.
> >
> > Well, I don't think anything was set in stone. If you have a compelling
> > reason why adding the new request gives you something over setting w8
> > directly, then we can extend ptrace.
>
> Yeah, I think I may have to change my mind. Looking into __secure_computing(),
> I found the code below:
>
> > case SECCOMP_MODE_FILTER:
> > case SECCOMP_RET_TRACE:
> > ...
> > if (syscall_get_nr(current, regs) < 0)
> > goto skip;
>
> This implies that we should modify syscallno *before* __secure_computing()
> returns.
Why does it imply that? There are four competing entities here:
- seccomp
- tracehook
- ftrace (trace_sys_*)
- audit
With the exception of ftrace, they can all potentially rewrite the pt_regs
(the code you cite above is just below a ptrace_event call), so we have
to choose some order in which to call them.
On entry, x86 and arm call them in the order I listed above, so it seems
sensible to follow that.
> I assumed, in my next version, we could skip a system call by overwriting
> syscallno with x8 in syscall_trace_enter() after __secure_computing()
> returns 0, and it actually works.
Why does overwriting the syscallno with x8 skip the syscall?
I thought the idea was that we would save w8 prior to each call that could
change the pt_regs, then if it was changed to -1 we would replace it with
the saved value and return -1? The only confusion I have is whether we
should call the exit hooks after skipping a syscall. I *think* x86 does
call them, but ARM doesn't. Andy says this can trigger an OOPs:
http://lists.infradead.org/pipermail/linux-arm-kernel/2014-July/274988.html
so we should fix that for ARM while we're here.
Will
next prev parent reply other threads:[~2014-08-12 9:41 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
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 [this message]
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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