Re: [PATCH v6 4/4] x86/ldt: Make modify_ldt optional

[Ingo Molnar <mingo@kernel.org>]

* Andy Lutomirski <luto@kernel.org> wrote:

> The modify_ldt syscall exposes a large attack surface and is
> unnecessary for modern userspace.  Make it optional.
> 
> Reviewed-by: Kees Cook <keescook@chromium.org>
> Signed-off-by: Andy Lutomirski <luto@kernel.org>
> ---
>  arch/x86/Kconfig                   | 17 +++++++++++++++++
>  arch/x86/include/asm/mmu.h         |  2 ++
>  arch/x86/include/asm/mmu_context.h | 28 +++++++++++++++++++++-------
>  arch/x86/kernel/Makefile           |  3 ++-
>  arch/x86/kernel/cpu/perf_event.c   |  4 ++++
>  arch/x86/kernel/process_64.c       |  2 ++
>  arch/x86/kernel/step.c             |  2 ++
>  kernel/sys_ni.c                    |  1 +
>  8 files changed, 51 insertions(+), 8 deletions(-)

btw., I fixed a (rare) build failure on MATH_EMULATION=y && !MODIFY_LDT_SYSCALL:

  arch/x86/math-emu/fpu_system.h:21:71: error: ‘mm_context_t’ has no member named ‘ldt’

I took the easy fix: made MATH_EMULATION depend on MODIFY_LDT_SYSCALL for now.

Thanks,

	Ingo