It doesn't make sense to have HARDENED_USERCOPY when either /dev/kmem is
enabled or /dev/mem can be used to read kernel memory.
v2: add !MMU depend as well
Signed-off-by: Tycho Andersen <[email protected]>
CC: Kees Cook <[email protected]>
CC: "Serge E. Hallyn" <[email protected]>
CC: James Morris <[email protected]>
---
security/Kconfig | 2 ++
1 file changed, 2 insertions(+)
diff --git a/security/Kconfig b/security/Kconfig
index 3ff1bf9..aeabd40 100644
--- a/security/Kconfig
+++ b/security/Kconfig
@@ -142,6 +142,8 @@ config HARDENED_USERCOPY
bool "Harden memory copies between kernel and userspace"
depends on HAVE_ARCH_HARDENED_USERCOPY
depends on HAVE_HARDENED_USERCOPY_ALLOCATOR
+ depends on !DEVKMEM
+ depends on !ARCH_HAS_DEVMEM_IS_ALLOWED || STRICT_DEVMEM || !MMU
select BUG
help
This option checks for obviously wrong memory regions when
--
2.7.4
On Thu, Mar 9, 2017 at 9:29 AM, Tycho Andersen <[email protected]> wrote:
> It doesn't make sense to have HARDENED_USERCOPY when either /dev/kmem is
> enabled or /dev/mem can be used to read kernel memory.
>
> v2: add !MMU depend as well
Sorry I keep revising my thoughts on this... so, the bad combos, IMO,
are /dev/kmem or /dev/mem. kmem is easy: we unconditionally require
!DEVKMEM. The /dev/mem one continues to hurt my head, but here's my
current thinking (which, if it seems correct should likely be
reflected in the commit message):
The following cases for /dev/mem should be safe:
- /dev/mem entirely disabled (!DEVMEM)
- /dev/mem with strict checking (STRICT_DEVMEM)
Everything else is not okay, i.e. if an architecture lacks
ARCH_HAS_DEVMEM_IS_ALLOWED, we must reject DEVMEM entirely since it
cannot select STRICT_DEVMEM.
So, sorry for the confusion, but I think this is the correct combo:
depends on !DEVKMEM
depends on !DEVMEM || STRICT_DEVMEM
That should cover it, unless I'm still thinking sideways.
-Kees
>
> Signed-off-by: Tycho Andersen <[email protected]>
> CC: Kees Cook <[email protected]>
> CC: "Serge E. Hallyn" <[email protected]>
> CC: James Morris <[email protected]>
> ---
> security/Kconfig | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/security/Kconfig b/security/Kconfig
> index 3ff1bf9..aeabd40 100644
> --- a/security/Kconfig
> +++ b/security/Kconfig
> @@ -142,6 +142,8 @@ config HARDENED_USERCOPY
> bool "Harden memory copies between kernel and userspace"
> depends on HAVE_ARCH_HARDENED_USERCOPY
> depends on HAVE_HARDENED_USERCOPY_ALLOCATOR
> + depends on !DEVKMEM
> + depends on !ARCH_HAS_DEVMEM_IS_ALLOWED || STRICT_DEVMEM || !MMU
> select BUG
> help
> This option checks for obviously wrong memory regions when
> --
> 2.7.4
>
--
Kees Cook
Pixel Security