Re: [RESEND PATCH v4 2/2] arm64: Add seccomp support

[AKASHI Takahiro]

Will,

>  (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.

So, is this the conclusion that I should follow?

-Takahiro AKASHI


On 07/09/2014 01:12 PM, Will Deacon wrote:
> Hi Akashi,
>
> On Fri, Jul 04, 2014 at 08:31:55AM +0100, AKASHI Takahiro wrote:
> > secure_computing() should always be called first in syscall_trace_enter().
> > If it returns non-zero, we should stop further handling. Then that system
> > call may eventually fail, be trapped or the process itself be killed
> > depending on loaded rules.
> > In this case, syscall_trace_enter() returns a dedicated value in order to
> > skip a normal syscall table lookup because a seccomp rule may have already
> > overridden errno.
>
> [...]
>
> > diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
> > index 70526cf..baab5fc 100644
> > --- a/arch/arm64/kernel/ptrace.c
> > +++ b/arch/arm64/kernel/ptrace.c
> > @@ -21,12 +21,14 @@
> >
> >   #include <linux/audit.h>
> >   #include <linux/compat.h>
> > +#include <linux/errno.h>
> >   #include <linux/kernel.h>
> >   #include <linux/sched.h>
> >   #include <linux/mm.h>
> >   #include <linux/smp.h>
> >   #include <linux/ptrace.h>
> >   #include <linux/user.h>
> > +#include <linux/seccomp.h>
> >   #include <linux/security.h>
> >   #include <linux/init.h>
> >   #include <linux/signal.h>
> > @@ -1109,6 +1111,10 @@ static void tracehook_report_syscall(struct pt_regs *regs,
> >
> >   asmlinkage int syscall_trace_enter(struct pt_regs *regs)
> >   {
> > +	if (secure_computing(regs->syscallno) == -1)
> > +		/* seccomp failures shouldn't expose any additional code. */
> > +		return -EPERM;
> > +
> >   	if (test_thread_flag(TIF_SYSCALL_TRACE))
> >   		tracehook_report_syscall(regs, PTRACE_SYSCALL_ENTER);
>
> We return regs->syscallno immediately after this, so we have the same issue
> that Kees identified for arch/arm/. Did you follow the discussion I had with
> Andy?
>
> Will
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