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SubjectRe: [PATCH 04/30] x86, kaiser: disable global pages by default with KAISER
On Wed, Nov 08, 2017 at 11:46:53AM -0800, Dave Hansen wrote:
>
> From: Dave Hansen <dave.hansen@linux.intel.com>
>
> Global pages stay in the TLB across context switches. Since all
> contexts share the same kernel mapping, we use global pages to
> allow kernel entries in the TLB to survive when we context
> switch.
>
> But, even having these entries in the TLB opens up something that
> an attacker can use [1].
>
> Disable global pages so that kernel TLB entries are flushed when
> we run userspace. This way, all accesses to kernel memory result
> in a TLB miss whether there is good data there or not. Without
> this, even when KAISER switches pages tables, the kernel entries
> might remain in the TLB.
>
> We keep _PAGE_GLOBAL available so that we can use it for things
> that are global even with KAISER like the entry/exit code and
> data.
>
> 1. The double-page-fault attack:
> http://www.ieee-security.org/TC/SP2013/papers/4977a191.pdf
>
> Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
> Cc: Moritz Lipp <moritz.lipp@iaik.tugraz.at>
> Cc: Daniel Gruss <daniel.gruss@iaik.tugraz.at>
> Cc: Michael Schwarz <michael.schwarz@iaik.tugraz.at>
> Cc: Richard Fellner <richard.fellner@student.tugraz.at>
> Cc: Andy Lutomirski <luto@kernel.org>
> Cc: Linus Torvalds <torvalds@linux-foundation.org>
> Cc: Kees Cook <keescook@google.com>
> Cc: Hugh Dickins <hughd@google.com>
> Cc: x86@kernel.org
> ---
>
> b/arch/x86/include/asm/pgtable_types.h | 14 +++++++++++++-
> b/arch/x86/mm/pageattr.c | 16 ++++++++--------
> 2 files changed, 21 insertions(+), 9 deletions(-)

Reviewed-by: Borislav Petkov <bp@suse.de>

--
Regards/Gruss,
Boris.

Good mailing practices for 400: avoid top-posting and trim the reply.

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