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SubjectRe: [PATCH v2 09/18] x86/asm: Move SYSENTER_stack to the beginning of struct tss_struct
On Wed, Nov 22, 2017 at 5:44 AM, Andy Lutomirski <luto@kernel.org> wrote:
> I want SYSENTER_stack to have reliable overflow detection, which
> means that it needs to be at the bottom of a page, not the top.
> Move it to the beginning of struct tss_struct and page-align it.
>
> Also add an assertion to make sure that the fixed hardware TSS
> doesn't cross a page boundary.
>
> Signed-off-by: Andy Lutomirski <luto@kernel.org>
> ---
> arch/x86/include/asm/processor.h | 21 ++++++++++++---------
> arch/x86/kernel/cpu/common.c | 22 ++++++++++++++++++++++
> 2 files changed, 34 insertions(+), 9 deletions(-)
>
> diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
> index d32a3c88a968..8f5dac9dfbdc 100644
> --- a/arch/x86/include/asm/processor.h
> +++ b/arch/x86/include/asm/processor.h
> @@ -327,7 +327,16 @@ struct x86_hw_tss {
>
> struct tss_struct {
> /*
> - * The hardware state:
> + * Space for the temporary SYSENTER stack, used for SYSENTER
> + * and the entry trampoline as well.
> + */
> + unsigned long SYSENTER_stack_canary;
> + unsigned long SYSENTER_stack[64];
> +
> + /*
> + * The fixed hardware portion. This must not cross a page boundary
> + * at risk of violating the SDM's advice and potentially triggering
> + * errata.
> */
> struct x86_hw_tss x86_tss;
>
> @@ -338,15 +347,9 @@ struct tss_struct {
> * be within the limit.
> */
> unsigned long io_bitmap[IO_BITMAP_LONGS + 1];
> +} __attribute__((__aligned__(PAGE_SIZE)));
>
> - /*
> - * Space for the temporary SYSENTER stack.
> - */
> - unsigned long SYSENTER_stack_canary;
> - unsigned long SYSENTER_stack[64];
> -} ____cacheline_aligned;

You may also move this initializer in process.c:

.SYSENTER_stack_canary = STACK_END_MAGIC,

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