Re: [RFC PATCH 9/9] powerpc/configs/skiroot: Enable some more hardening options
Joel Stanley writes: > On Thu, 16 Jan 2020 at 01:48, Michael Ellerman wrote: >> >> Enable more hardening options. >> >> Note BUG_ON_DATA_CORRUPTION selects DEBUG_LIST and is essentially just >> a synonym for it. >> >> DEBUG_SG, DEBUG_NOTIFIERS, DEBUG_LIST, DEBUG_CREDENTIALS and >> SCHED_STACK_END_CHECK should all be low overhead and just add a few >> extra checks. >> >> Unselecting SLAB_MERGE_DEFAULT causes the SLAB to use more memory, but >> the skiroot kernel shouldn't be memory constrained on any of our >> systems, all it does is run a small bootloader. > > Why do we unselect it? The help text pretty much explains it: config SLAB_MERGE_DEFAULT bool "Allow slab caches to be merged" default y help For reduced kernel memory fragmentation, slab caches can be merged when they share the same size and other characteristics. This carries a risk of kernel heap overflows being able to overwrite objects from merged caches (and more easily control cache layout), which makes such heap attacks easier to exploit by attackers. By keeping caches unmerged, these kinds of exploits can usually only damage objects in the same cache. To disable merging at runtime, "slab_nomerge" can be passed on the kernel command line. So unselecting it uses a bit more memory but has some security/robustness benefit. I should probably also mention that it essentially has no effect because we're also enabling SLUB_DEBUG_ON, and that causes some of the flags in SLAB_NEVER_MERGE to be set, which also disables merging. cheers
Re: [RFC PATCH 9/9] powerpc/configs/skiroot: Enable some more hardening options
On Thu, 16 Jan 2020 at 01:48, Michael Ellerman wrote: > > Enable more hardening options. > > Note BUG_ON_DATA_CORRUPTION selects DEBUG_LIST and is essentially just > a synonym for it. > > DEBUG_SG, DEBUG_NOTIFIERS, DEBUG_LIST, DEBUG_CREDENTIALS and > SCHED_STACK_END_CHECK should all be low overhead and just add a few > extra checks. > > Unselecting SLAB_MERGE_DEFAULT causes the SLAB to use more memory, but > the skiroot kernel shouldn't be memory constrained on any of our > systems, all it does is run a small bootloader. Why do we unselect it? > SLAB_FREELIST_RANDOM, and SLUB_DEBUG_ON will add some overhead to the > SLAB allocator, but nothing that should be meaningful for skiroot. > > Signed-off-by: Michael Ellerman Acked-by: Joel Stanley > --- > arch/powerpc/configs/skiroot_defconfig | 8 > 1 file changed, 8 insertions(+) > > diff --git a/arch/powerpc/configs/skiroot_defconfig > b/arch/powerpc/configs/skiroot_defconfig > index 12c96c8b0c1d..59c2de904fda 100644 > --- a/arch/powerpc/configs/skiroot_defconfig > +++ b/arch/powerpc/configs/skiroot_defconfig > @@ -23,6 +23,8 @@ CONFIG_EXPERT=y > # CONFIG_AIO is not set > CONFIG_PERF_EVENTS=y > # CONFIG_COMPAT_BRK is not set > +# CONFIG_SLAB_MERGE_DEFAULT is not set > +CONFIG_SLAB_FREELIST_RANDOM=y > CONFIG_SLAB_FREELIST_HARDENED=y > CONFIG_PPC64=y > CONFIG_ALTIVEC=y > @@ -293,6 +295,8 @@ CONFIG_LIBCRC32C=y > # CONFIG_XZ_DEC_SPARC is not set > CONFIG_PRINTK_TIME=y > CONFIG_MAGIC_SYSRQ=y > +CONFIG_SLUB_DEBUG_ON=y > +CONFIG_SCHED_STACK_END_CHECK=y > CONFIG_DEBUG_STACKOVERFLOW=y > CONFIG_PANIC_ON_OOPS=y > CONFIG_SOFTLOCKUP_DETECTOR=y > @@ -301,6 +305,10 @@ CONFIG_HARDLOCKUP_DETECTOR=y > CONFIG_BOOTPARAM_HARDLOCKUP_PANIC=y > CONFIG_WQ_WATCHDOG=y > # CONFIG_SCHED_DEBUG is not set > +CONFIG_DEBUG_SG=y > +CONFIG_DEBUG_NOTIFIERS=y > +CONFIG_BUG_ON_DATA_CORRUPTION=y > +CONFIG_DEBUG_CREDENTIALS=y > # CONFIG_FTRACE is not set > CONFIG_XMON=y > # CONFIG_RUNTIME_TESTING_MENU is not set > -- > 2.21.1 >
[RFC PATCH 9/9] powerpc/configs/skiroot: Enable some more hardening options
Enable more hardening options. Note BUG_ON_DATA_CORRUPTION selects DEBUG_LIST and is essentially just a synonym for it. DEBUG_SG, DEBUG_NOTIFIERS, DEBUG_LIST, DEBUG_CREDENTIALS and SCHED_STACK_END_CHECK should all be low overhead and just add a few extra checks. Unselecting SLAB_MERGE_DEFAULT causes the SLAB to use more memory, but the skiroot kernel shouldn't be memory constrained on any of our systems, all it does is run a small bootloader. SLAB_FREELIST_RANDOM, and SLUB_DEBUG_ON will add some overhead to the SLAB allocator, but nothing that should be meaningful for skiroot. Signed-off-by: Michael Ellerman --- arch/powerpc/configs/skiroot_defconfig | 8 1 file changed, 8 insertions(+) diff --git a/arch/powerpc/configs/skiroot_defconfig b/arch/powerpc/configs/skiroot_defconfig index 12c96c8b0c1d..59c2de904fda 100644 --- a/arch/powerpc/configs/skiroot_defconfig +++ b/arch/powerpc/configs/skiroot_defconfig @@ -23,6 +23,8 @@ CONFIG_EXPERT=y # CONFIG_AIO is not set CONFIG_PERF_EVENTS=y # CONFIG_COMPAT_BRK is not set +# CONFIG_SLAB_MERGE_DEFAULT is not set +CONFIG_SLAB_FREELIST_RANDOM=y CONFIG_SLAB_FREELIST_HARDENED=y CONFIG_PPC64=y CONFIG_ALTIVEC=y @@ -293,6 +295,8 @@ CONFIG_LIBCRC32C=y # CONFIG_XZ_DEC_SPARC is not set CONFIG_PRINTK_TIME=y CONFIG_MAGIC_SYSRQ=y +CONFIG_SLUB_DEBUG_ON=y +CONFIG_SCHED_STACK_END_CHECK=y CONFIG_DEBUG_STACKOVERFLOW=y CONFIG_PANIC_ON_OOPS=y CONFIG_SOFTLOCKUP_DETECTOR=y @@ -301,6 +305,10 @@ CONFIG_HARDLOCKUP_DETECTOR=y CONFIG_BOOTPARAM_HARDLOCKUP_PANIC=y CONFIG_WQ_WATCHDOG=y # CONFIG_SCHED_DEBUG is not set +CONFIG_DEBUG_SG=y +CONFIG_DEBUG_NOTIFIERS=y +CONFIG_BUG_ON_DATA_CORRUPTION=y +CONFIG_DEBUG_CREDENTIALS=y # CONFIG_FTRACE is not set CONFIG_XMON=y # CONFIG_RUNTIME_TESTING_MENU is not set -- 2.21.1
