On Fri, Jun 29, 2018 at 01:27:08PM -0700, Kees Cook wrote:
> On Fri, Jun 29, 2018 at 1:04 PM, Kamal Mostafa <ka...@canonical.com> wrote:
> > Allows for CONFIG_HARDENED_USERCOPY without CONFIG_BUG.
> >
> > Signed-off-by: Kamal Mostafa <ka...@canonical.com>
> > ---
> > security/Kconfig | 1 -
> > 1 file changed, 1 deletion(-)
> >
> > diff --git a/security/Kconfig b/security/Kconfig
> > index c430206..7667774 100644
> > --- a/security/Kconfig
> > +++ b/security/Kconfig
> > @@ -153,7 +153,6 @@ config HAVE_HARDENED_USERCOPY_ALLOCATOR
> > config HARDENED_USERCOPY
> > bool "Harden memory copies between kernel and userspace"
> > depends on HAVE_HARDENED_USERCOPY_ALLOCATOR
> > - select BUG
> > imply STRICT_DEVMEM
> > help
> > This option checks for obviously wrong memory regions when
>
> Do the lkdtm tests for usercopy correctly halt the kernel thread if
> CONFIG_BUG is removed?
>
Yes, they do...
With this config (specifically disabling 'FALLBACK'):
CONFIG_HARDENED_USERCOPY=y
# CONFIG_HARDENED_USERCOPY_FALLBACK is not set
# CONFIG_BUG is not set
I ran the usercopy tests as follows:
modprobe lkdtm
cd /sys/kernel/debug/provoke-crash
cat DIRECT | grep USERCOPY | while read x ; do echo $x | tee DIRECT || echo
$?; done
Resulting in this command line output:
USERCOPY_HEAP_SIZE_TO
139
USERCOPY_HEAP_SIZE_FROM
139
USERCOPY_HEAP_WHITELIST_TO
139
USERCOPY_HEAP_WHITELIST_FROM
139
USERCOPY_STACK_FRAME_TO
139
USERCOPY_STACK_FRAME_FROM
139
USERCOPY_STACK_BEYOND
139
USERCOPY_KERNEL
139
Each test case yields kernel log output like:
lkdtm: Performing direct entry USERCOPY_HEAP_SIZE_TO
lkdtm: attempting good copy_to_user of correct size
lkdtm: attempting bad copy_to_user of too large size
usercopy: Kernel memory exposure attempt detected from SLUB object
'kmalloc-1024' (offset 16, size 1024)!
invalid opcode: 0000 [#17] SMP PTI
... {panic dump} ...
Each 'tee' gets terminated with SIGSEGV and no instances appear of the
lkdtm/usercopy.c warning "copy_{to/from}_user failed, but lacked Oops".
If I leave CONFIG_HARDENED_USERCOPY_FALLBACK=y then the pair of
WHITELIST tests don't trigger a panic or SIGSEGV, as expected.
-Kamal
