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SubjectRe: [PATCH] x86/mm: Set NX on gap between __ex_table and rodata
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On Thu, Oct 1, 2015 at 6:04 AM, Stephen Smalley <sds@tycho.nsa.gov> wrote:
> Unused space between the end of __ex_table and the start of rodata
> can be left W+x in the kernel page tables. Extend the setting
> of the NX bit to cover this gap by starting from text_end rather than
> rodata_start.
>
> Before:
> ---[ High Kernel Mapping ]---
> 0xffffffff80000000-0xffffffff81000000 16M pmd
> 0xffffffff81000000-0xffffffff81600000 6M ro PSE GLB x pmd
> 0xffffffff81600000-0xffffffff81754000 1360K ro GLB x pte
> 0xffffffff81754000-0xffffffff81800000 688K RW GLB x pte
> 0xffffffff81800000-0xffffffff81a00000 2M ro PSE GLB NX pmd
> 0xffffffff81a00000-0xffffffff81b3b000 1260K ro GLB NX pte
> 0xffffffff81b3b000-0xffffffff82000000 4884K RW GLB NX pte
> 0xffffffff82000000-0xffffffff82200000 2M RW PSE GLB NX pmd
> 0xffffffff82200000-0xffffffffa0000000 478M pmd
>
> After:
> ---[ High Kernel Mapping ]---
> 0xffffffff80000000-0xffffffff81000000 16M pmd
> 0xffffffff81000000-0xffffffff81600000 6M ro PSE GLB x pmd
> 0xffffffff81600000-0xffffffff81754000 1360K ro GLB x pte
> 0xffffffff81754000-0xffffffff81800000 688K RW GLB NX pte
> 0xffffffff81800000-0xffffffff81a00000 2M ro PSE GLB NX pmd
> 0xffffffff81a00000-0xffffffff81b3b000 1260K ro GLB NX pte
> 0xffffffff81b3b000-0xffffffff82000000 4884K RW GLB NX pte
> 0xffffffff82000000-0xffffffff82200000 2M RW PSE GLB NX pmd
> 0xffffffff82200000-0xffffffffa0000000 478M pmd
>
> Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>

Acked-by: Kees Cook <keescook@chromium.org>

-Kees

> ---
> arch/x86/mm/init_64.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
> index 30564e2..df48430 100644
> --- a/arch/x86/mm/init_64.c
> +++ b/arch/x86/mm/init_64.c
> @@ -1132,7 +1132,7 @@ void mark_rodata_ro(void)
> * has been zapped already via cleanup_highmem().
> */
> all_end = roundup((unsigned long)_brk_end, PMD_SIZE);
> - set_memory_nx(rodata_start, (all_end - rodata_start) >> PAGE_SHIFT);
> + set_memory_nx(text_end, (all_end - text_end) >> PAGE_SHIFT);
>
> rodata_test();
>
> --
> 2.1.0
>



--
Kees Cook
Chrome OS Security


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