[PATCH 08/10] parisc: fix livelock in uaccess

[Guenter Roeck]

On Tue, Jan 31, 2023 at 08:06:27PM +0000, Al Viro wrote:
> parisc equivalent of 26178ec11ef3 "x86: mm: consolidate VM_FAULT_RETRY handling"
> If e.g. get_user() triggers a page fault and a fatal signal is caught, we might
> end up with handle_mm_fault() returning VM_FAULT_RETRY and not doing anything
> to page tables.  In such case we must *not* return to the faulting insn -
> that would repeat the entire thing without making any progress; what we need
> instead is to treat that as failed (user) memory access.
> 
> Signed-off-by: Al Viro <viro at zeniv.linux.org.uk>
> ---
>  arch/parisc/mm/fault.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/parisc/mm/fault.c b/arch/parisc/mm/fault.c
> index 869204e97ec9..bb30ff6a3e19 100644
> --- a/arch/parisc/mm/fault.c
> +++ b/arch/parisc/mm/fault.c
> @@ -308,8 +308,11 @@ void do_page_fault(struct pt_regs *regs, unsigned long code,
>  
>  	fault = handle_mm_fault(vma, address, flags, regs);
>  
> -	if (fault_signal_pending(fault, regs))
> +	if (fault_signal_pending(fault, regs)) {
> +		if (!user_mode(regs))
> +			goto no_context;

0-day rightfully complains that this leaves 'msg' uninitialized.

arch/parisc/mm/fault.c:427 do_page_fault() error: uninitialized symbol 'msg'

Guenter

>  		return;
> +	}
>  
>  	/* The fault is fully completed (including releasing mmap lock) */
>  	if (fault & VM_FAULT_COMPLETED)