| Message ID | 1489080561-30786-1-git-send-email-tycho@docker.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Thu, Mar 9, 2017 at 9:29 AM, Tycho Andersen <tycho@docker.com> 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 <tycho@docker.com> > CC: Kees Cook <keescook@chromium.org> > CC: "Serge E. Hallyn" <serge@hallyn.com> > CC: James Morris <james.l.morris@oracle.com> > --- > 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 >
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
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 <tycho@docker.com> CC: Kees Cook <keescook@chromium.org> CC: "Serge E. Hallyn" <serge@hallyn.com> CC: James Morris <james.l.morris@oracle.com> --- security/Kconfig | 2 ++ 1 file changed, 2 insertions(+)