Re: [PATCH] x86: make sure IDT is page aligned

H. Peter Anvin
2013-07-12T22:27:57Z

On 07/12/2013 11:30 AM, Kees Cook wrote:
> Since the IDT is referenced from a fixmap, make sure it is page aligned.
> This avoids the risk of it ever being moved in the bss and having the
> fixmap fail.
>
> Signed-off-by: Kees Cook <keescook@chromium.org>
> Reported-by: PaX Team <pageexec@freemail.hu>
> Cc: stable@vger.kernel.org
> ---
> arch/x86/kernel/head_32.S | 2 +-
> arch/x86/kernel/head_64.S | 2 +-
> 2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kernel/head_32.S b/arch/x86/kernel/head_32.S
> index e65ddc6..3526dd1 100644
> --- a/arch/x86/kernel/head_32.S
> +++ b/arch/x86/kernel/head_32.S
> @@ -734,7 +734,7 @@ boot_gdt_descr:
> .word __BOOT_DS+7
> .long boot_gdt - __PAGE_OFFSET
>
> - .word 0 # 32-bit align idt_desc.address
> + .word PAGE_SIZE # page align idt_desc.address
> idt_descr:
> .word IDT_ENTRIES*8-1 # idt contains 256 entries
> .long idt_table
> diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
> index 5e4d8a8..77e6d3e 100644
> --- a/arch/x86/kernel/head_64.S
> +++ b/arch/x86/kernel/head_64.S
> @@ -513,7 +513,7 @@ ENTRY(phys_base)
> #include "../../x86/xen/xen-head.S"
>
> .section .bss, "aw", @nobits
> - .align L1_CACHE_BYTES
> + .align PAGE_SIZE
> ENTRY(idt_table)
> .skip IDT_ENTRIES * 16
>
>

You are aligning the IDT *descriptor*, not the IDT itself?

-hpa