Re: [PATCH 4/5] arm64: dovetail: Helper functions for signal frame setup and restore

[Richard Weinberger <richard@sigma-star.at>]

On Dienstag, 8. April 2025 15:05 Florian Bezdeka wrote:
> > +	if (regs->sp & 15)
> > +		goto out;
> 
> - Where is this magic 15 coming from?

The stack needs to be word aligned.
This was taken from the Linux side.

> - return -EFAULT; would also work and save us one label.

Ok.

> 
> > +
> > +	frame = (struct rt_sigframe __user *)regs->sp;
> > +
> > +	pagefault_disable();
> > +
> > +	if (!access_ok(frame, sizeof (*frame)))
> > +		goto out_pfe;
> > +
> > +	if (restore_sigframe(regs, frame, &ua_state))
> > +		goto out_pfe;
> > +
> > +	restore_user_access_state(&ua_state);
> > +
> > +	ret = 0;
> > +
> > +out_pfe:
> > +	pagefault_enable();
> > +out:
> > +	return ret;
> > +}
> > +
> > +static int dovetail_restore_32_rt_signal_frame(struct pt_regs *regs)
> > +{
> > +	struct compat_rt_sigframe __user *frame;
> > +	int ret = 0;

That should be pre-initialized to -EFAULT. :-S

> > +	if (regs->sp & 7)

Given this a second thought, the check should inspect ->compat_sp, no ->sp.

> > +		goto out;
> 
> Same as above. 
> - Magic 7

The stack needs to be word aligned.

> - Is the error reporting really correct here? We would return 0.

Yes.

Thanks,
//richard

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