Re: [PATCH] x86_64: another fix for canonical RIPs during signal handling

[Andi Kleen <ak@suse.de>]

On Thursday 22 June 2006 23:06, Willy Tarreau wrote:
> 
> I've been reported by the PaX Team that the following fix left a
> small hole :
> 
> [PATCH] Always check that RIPs are canonical during signal handling
> 
> +	if (regs->rip >= TASK_SIZE && regs->rip < VSYSCALL_START) {
> +		regs->rip = 0;
> +		return -EFAULT;
> +	}
> 
> ...
> 
> +	if (regs->rip >= TASK_SIZE) {
> +		if (sig == SIGSEGV)
> +			ka->sa.sa_handler = SIG_DFL;
> +		regs->rip = 0;
> +	}
> 
> "the wrong part is regs->rip=0, i guess the intention was to cause a
>  SIGSEGV upon returning to userland, but 0 is a valid userland address,
>  an application may very well have something mapped there. the correct
>  value would be ~0UL as it's guaranteed to fault on linux."
> 
> This explanation makes sense, so here's the patch. Andi, would you please
> review and confirm ? Thanks in advance.

I don't think it's a real problem.

The patch is not wrong, but also doesn't fix something that needs
to be fixed.

-Andi