Subject: Re: powerpc/mm/radix: Only add X for pages overlapping kernel text

From: Michael Ellerman <[email-masked]>
Date: Mon, 19 Jun 2017 22:25:36 +1000 (AEST)

On Tue, 2017-06-06 at 05:48:57 UTC, Michael Ellerman wrote:
> Currently we map the whole linear mapping with PAGE_KERNEL_X. Instead we
> should check if the page overlaps the kernel text and only then add
> PAGE_KERNEL_X.
> 
> Note that we still use 1G pages if they're available, so this will
> typically still result in a 1G executable page at KERNELBASE. So this fix is
> primarily useful for catching stray branches to high linear mapping addresses.
> 
> Without this patch, we can execute at 1G in xmon using:
> 
>   0:mon> m c000000040000000
>   c000000040000000  00 l
>   c000000040000000  00000000 01006038
>   c000000040000004  00000000 2000804e
>   c000000040000008  00000000 x
>   0:mon> di c000000040000000
>   c000000040000000  38600001      li      r3,1
>   c000000040000004  4e800020      blr
>   0:mon> p c000000040000000
>   return value is 0x1
> 
> After we get a 400 as expected:
> 
>   0:mon> p c000000040000000
>   *** 400 exception occurred
> 
> Fixes: 2bfd65e45e87 ("powerpc/mm/radix: Add radix callbacks for early init routines")
> Cc: [email-masked] # v4.7+
> Signed-off-by: Michael Ellerman <[email-masked]>
> Reviewed-by: Aneesh Kumar K.V <[email-masked]>
> Acked-by: Balbir Singh <[email-masked]>

Applied to powerpc next.

https://git.kernel.org/powerpc/c/9abcc981de9775659a0f6e4a52a344

cheers