Re: [PATCH v9 1/6] arm64: ptrace: add NT_ARM_SYSTEM_CALL regset

[AKASHI Takahiro]

On 11/27/2014 11:10 PM, Will Deacon wrote:
> On Thu, Nov 27, 2014 at 05:53:36AM +0000, AKASHI Takahiro wrote:
> > On 11/26/2014 09:41 PM, Will Deacon wrote:
> > > On Wed, Nov 26, 2014 at 04:49:46AM +0000, AKASHI Takahiro wrote:
> > > > This regeset is intended to be used to get and set a system call number
> > > > while tracing.
> > > > There was some discussion about possible approaches to do so:
> > > >
> > > > (1) modify x8 register with ptrace(PTRACE_SETREGSET) indirectly,
> > > >       and update regs->syscallno later on in syscall_trace_enter(), or
> > > > (2) define a dedicated regset for this purpose as on s390, or
> > > > (3) support ptrace(PTRACE_SET_SYSCALL) as on arch/arm
> > > >
> > > > Thinking of the fact that user_pt_regs doesn't expose 'syscallno' to
> > > > tracer as well as that secure_computing() expects a changed syscall number,
> > > > especially case of -1, to be visible before this function returns in
> > > > syscall_trace_enter(), (1) doesn't work well.
> > > > We will take (2) since it looks much cleaner.
> > > >
> > > > Signed-off-by: AKASHI Takahiro <takahiro.akashi@xxxxxxxxxx>
> > > > ---
> > > >    arch/arm64/kernel/ptrace.c |   35 +++++++++++++++++++++++++++++++++++
> > > >    include/uapi/linux/elf.h   |    1 +
> > > >    2 files changed, 36 insertions(+)
> > > >
> > > > diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
> > > > index 8a4ae8e..8b98781 100644
> > > > --- a/arch/arm64/kernel/ptrace.c
> > > > +++ b/arch/arm64/kernel/ptrace.c
> > > > @@ -551,6 +551,32 @@ static int tls_set(struct task_struct *target, const struct user_regset *regset,
> > > >    	return ret;
> > > >    }
> > > >
> > > > +static int system_call_get(struct task_struct *target,
> > > > +			   const struct user_regset *regset,
> > > > +			   unsigned int pos, unsigned int count,
> > > > +			   void *kbuf, void __user *ubuf)
> > > > +{
> > > > +	struct pt_regs *regs = task_pt_regs(target);
> > > > +
> > > > +	return user_regset_copyout(&pos, &count, &kbuf, &ubuf,
> > > > +				   &regs->syscallno, 0, -1);
> > >
> > > Does this work for big-endian machines? regs->syscallno is a u64, but the
> > > regset defines it as an int. I think you need to copy to a temporary
> > > register first.
> >
> > Right. I will fix it.
> > Do you prefer to use s32, instead of int, like other regsets?
>
> I don't have a preference either way.
>
> It would be great to have a new revision of these patches ASAP if you're
> targetting 3.19.

Yeah, definitely.

-Takahiro AKASHI

> Will
> --
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@xxxxxxxxxxxxxxx
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at  http://www.tux.org/lkml/
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/