Messages in this thread | | | Date | Thu, 3 Jul 2014 11:24:50 +0100 | From | Will Deacon <> | Subject | Re: [PATCH] arm: ptrace: fix syscall modification under PTRACE_O_TRACESECCOMP |
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On Thu, Jul 03, 2014 at 08:43:07AM +0100, AKASHI Takahiro wrote: > Hi Will,
Hi Akashi,
> On 06/24/2014 05:54 PM, Will Deacon wrote: > > On Mon, Jun 23, 2014 at 08:46:52PM +0100, Kees Cook wrote: > >> What's the state of seccomp on arm64? I saw a series back in March, > >> but nothing since then? It looked complete, but I haven't set up a > >> test environment yet to verify. > > > > I think Akashi was going to repost `real soon now' so we can include them > > for 3.17. He missed the merge window last time around. > > I took a quick look at the current implementation of ptrace. > ptrace(PTRACE_GETREGSET/SETREGSET), eventually gpr_get/set(), handles only > 'struct user_pt_regs', and we have no way to modify orig_x0 nor syscallno > in 'struct pt_regs' directly. > So it seems to me that we can't change a system call by ptrace(). > Do I misunderstand anything?
No, it looks like you have a point here. I don't think userspace has any business with orig_x0, but changing syscallno is certainly useful. I can think of two ways to fix this:
(1) Updating syscallno based on w8, but this ties us to the current ABI and could get messy if this register changes in the future.
(2) Adding a PTRACE_SET_SYSCALL request, like we have for arch/arm/, but that means adding arch-specific stuff to arch_ptrace (which currently goes straight to ptrace_request on arm64).
It looks like x86 uses orig_ax, which I *think* means we would go with (1) above if we followed their lead.
Anybody else have an opinion about this?
Will
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