From: will.deacon@arm.com (Will Deacon)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH v5 1/3] arm64: ptrace: reload a syscall number after ptrace operations
Date: Wed, 23 Jul 2014 09:25:05 +0100 [thread overview]
Message-ID: <20140723082505.GB27260@arm.com> (raw)
In-Reply-To: <53CF5E53.3060409@linaro.org>
On Wed, Jul 23, 2014 at 08:03:47AM +0100, AKASHI Takahiro wrote:
> On 07/23/2014 05:15 AM, Kees Cook wrote:
> > On Tue, Jul 22, 2014 at 2:14 AM, AKASHI Takahiro
> > <takahiro.akashi@linaro.org> wrote:
> >> asmlinkage int syscall_trace_enter(struct pt_regs *regs)
> >> {
> >> + unsigned long saved_x0, saved_x8;
> >> +
> >> + saved_x0 = regs->regs[0];
> >> + saved_x8 = regs->regs[8];
> >> +
> >> if (test_thread_flag(TIF_SYSCALL_TRACE))
> >> tracehook_report_syscall(regs, PTRACE_SYSCALL_ENTER);
> >>
> >> + regs->syscallno = regs->regs[8];
> >> + if ((long)regs->syscallno == ~0UL) { /* skip this syscall */
> >> + regs->regs[8] = saved_x8;
> >> + if (regs->regs[0] == saved_x0) /* not changed by user */
> >> + regs->regs[0] = -ENOSYS;
> >
> > I'm not sure this is right compared to other architectures. Generally
> > when a tracer performs a syscall skip, it's up to them to also adjust
> > the return value. They may want to be faking a syscall, and what if
> > the value they want to return happens to be what x0 was going into the
> > tracer? It would have no way to avoid this -ENOSYS case. I think
> > things are fine without this test.
>
> Yeah, I know this issue, but was not sure that setting a return value
> is mandatory. (x86 seems to return -ENOSYS by default if not explicitly
> specified.)
> Is "fake a system call" a more appropriate word than "skip"?
>
> I will defer to Will.
I agree with Kees -- iirc, I only suggested restoring x8.
Will
next prev parent reply other threads:[~2014-07-23 8:25 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 [this message]
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
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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