[PATCH] security/Kconfig: further restrict HARDENED_USERCOPY
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From: Kees Cook <hidden>
Date: 2017-03-09 19:18:49
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On Thu, Mar 9, 2017 at 9:29 AM, Tycho Andersen [off-list ref] 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
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Signed-off-by: Tycho Andersen <redacted> CC: Kees Cook <redacted> CC: "Serge E. Hallyn" <serge@hallyn.com> CC: James Morris <redacted> --- 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
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