Re: [PATCH 2/2] MIPS: Partially disable RIXI support.

[James Hogan <james.hogan@imgtec.com>]

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On 23/07/15 10:10, Ralf Baechle wrote:
> Execution of break instruction, trap instructions, emulation of unaligned
> loads or floating point instructions - anything that tries to read the
> instruction's opcode from userspace - needs read access to a page.
> 
> RIXI (Read Inhibit / Execute Inhibit) support however allows the creation of
> pags that are executable but not readable.  On such a mapping the attempted
> load of the opcode by the kernel is going to cause an endless loop of
> page faults.
> 
> The quick workaround for this is to disable the combinations that the kernel
> currently isn't able to handle which are executable mappings.
> 
> Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

Reviewed-by: James Hogan <james.hogan@imgtec.com>

Cheers
James

> ---
>  arch/mips/mm/cache.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/mips/mm/cache.c b/arch/mips/mm/cache.c
> index 77d96db..aab218c 100644
> --- a/arch/mips/mm/cache.c
> +++ b/arch/mips/mm/cache.c
> @@ -160,18 +160,18 @@ static inline void setup_protection_map(void)
>  		protection_map[1]  = __pgprot(_page_cachable_default | _PAGE_PRESENT | _PAGE_NO_EXEC);
>  		protection_map[2]  = __pgprot(_page_cachable_default | _PAGE_PRESENT | _PAGE_NO_EXEC | _PAGE_NO_READ);
>  		protection_map[3]  = __pgprot(_page_cachable_default | _PAGE_PRESENT | _PAGE_NO_EXEC);
> -		protection_map[4]  = __pgprot(_page_cachable_default | _PAGE_PRESENT | _PAGE_NO_READ);
> +		protection_map[4]  = __pgprot(_page_cachable_default | _PAGE_PRESENT);
>  		protection_map[5]  = __pgprot(_page_cachable_default | _PAGE_PRESENT);
> -		protection_map[6]  = __pgprot(_page_cachable_default | _PAGE_PRESENT | _PAGE_NO_READ);
> +		protection_map[6]  = __pgprot(_page_cachable_default | _PAGE_PRESENT);
>  		protection_map[7]  = __pgprot(_page_cachable_default | _PAGE_PRESENT);
>  
>  		protection_map[8]  = __pgprot(_page_cachable_default | _PAGE_PRESENT | _PAGE_NO_EXEC | _PAGE_NO_READ);
>  		protection_map[9]  = __pgprot(_page_cachable_default | _PAGE_PRESENT | _PAGE_NO_EXEC);
>  		protection_map[10] = __pgprot(_page_cachable_default | _PAGE_PRESENT | _PAGE_NO_EXEC | _PAGE_WRITE | _PAGE_NO_READ);
>  		protection_map[11] = __pgprot(_page_cachable_default | _PAGE_PRESENT | _PAGE_NO_EXEC | _PAGE_WRITE);
> -		protection_map[12] = __pgprot(_page_cachable_default | _PAGE_PRESENT | _PAGE_NO_READ);
> +		protection_map[12] = __pgprot(_page_cachable_default | _PAGE_PRESENT);
>  		protection_map[13] = __pgprot(_page_cachable_default | _PAGE_PRESENT);
> -		protection_map[14] = __pgprot(_page_cachable_default | _PAGE_PRESENT | _PAGE_WRITE  | _PAGE_NO_READ);
> +		protection_map[14] = __pgprot(_page_cachable_default | _PAGE_PRESENT | _PAGE_WRITE);
>  		protection_map[15] = __pgprot(_page_cachable_default | _PAGE_PRESENT | _PAGE_WRITE);
>  
>  	} else {
> 


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