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

[AKASHI Takahiro]

On 11/26/2014 09:41 PM, Will Deacon wrote:
> Hi Akashi,
>
> 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?


Thanks,
-Takahiro AKASHI

> Will
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