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@xxxxxxxxxxxxxx>
Reviewed-by: James Hogan <james.hogan@xxxxxxxxxx>
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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