linux-kernel - Re: [PATCH 2/2] mm: don't allow executable ioremap mappings

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Message-Id: <1629945413.hwbzjjtfbl.astroid@bobo.none>
Date:   Thu, 26 Aug 2021 12:46:34 +1000
From:   Nicholas Piggin <npiggin@...il.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Christoph Hellwig <hch@....de>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 2/2] mm: don't allow executable ioremap mappings

Excerpts from Christoph Hellwig's message of August 24, 2021 7:12 pm:
> There is no need to execute from iomem (and most platforms it is
> impossible anyway), so add the pgprot_nx() call similar to vmap.
> 
> Signed-off-by: Christoph Hellwig <hch@....de>
> ---
>  mm/vmalloc.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index e44983fb2d15..3055f04b486b 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -316,7 +316,7 @@ int ioremap_page_range(unsigned long addr, unsigned long end,
>  {
>  	int err;
>  
> -	err = vmap_range_noflush(addr, end, phys_addr, prot,
> +	err = vmap_range_noflush(addr, end, phys_addr, pgprot_nx(prot),
>  				 ioremap_max_page_shift);

I can't see why this is a problem. powerpcs can but it seems like a bad 
idea anyway.

Any point to a WARN_ON or return -EINVAL? Hmm, maybe that doesn't work 
for archs that don't support NX. We could add a check for ones that do 
support it though... But that's for another patch.

Thanks,
Nick