On Fri, 14 Nov 2014, Kees Cook wrote:
> When setting up permissions on kernel memory at boot, the end of the
> PMD that was split from bss remained executable. It should be NX like
> the rest. This performs a PMD alignment instead of a PAGE alignment to
> get the correct span of memory.
>
> Before:
> ---[ High Kernel Mapping ]---
> ...
> 0xffffffff8202d000-0xffffffff82200000 1868K RW GLB NX pte
> 0xffffffff82200000-0xffffffff82c00000 10M RW PSE GLB NX pmd
> 0xffffffff82c00000-0xffffffff82df5000 2004K RW GLB NX pte
> 0xffffffff82df5000-0xffffffff82e00000 44K RW GLB x pte
> 0xffffffff82e00000-0xffffffffc0000000 978M pmd
>
> After:
> ---[ High Kernel Mapping ]---
> ...
> 0xffffffff8202d000-0xffffffff82200000 1868K RW GLB NX pte
> 0xffffffff82200000-0xffffffff82e00000 12M RW PSE GLB NX pmd
> 0xffffffff82e00000-0xffffffffc0000000 978M pmd
>
> Signed-off-by: Kees Cook <keesc...@chromium.org>
> ---
> arch/x86/mm/init_64.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
> index 4cb8763868fc..7da7a4ab46f7 100644
> --- a/arch/x86/mm/init_64.c
> +++ b/arch/x86/mm/init_64.c
> @@ -1123,7 +1123,9 @@ void mark_rodata_ro(void)
> unsigned long end = (unsigned long) &__end_rodata_hpage_align;
> unsigned long text_end = PFN_ALIGN(&__stop___ex_table);
> unsigned long rodata_end = PFN_ALIGN(&__end_rodata);
> - unsigned long all_end = PFN_ALIGN(&_end);
> + /* End of kernel memory will span a PMD, so align to PMD. */
> + unsigned long all_end = (((unsigned long)(&_end) + (PMD_SIZE - 1))
> + & PMD_MASK);
I prefer to free the leftover pages like we do with the init
sections. In the above example it's only 44k, but it can be 2044k in
the worst case, which was enough to boot a embedded box 15 years ago :)
Thanks,
tglx
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
