On Mon 17-06-19 17:10:49, Alexander Potapenko wrote: > The new options are needed to prevent possible information leaks and > make control-flow bugs that depend on uninitialized values more > deterministic. > > init_on_alloc=1 makes the kernel initialize newly allocated pages and heap > objects with zeroes. Initialization is done at allocation time at the > places where checks for __GFP_ZERO are performed. > > init_on_free=1 makes the kernel initialize freed pages and heap objects > with zeroes upon their deletion. This helps to ensure sensitive data > doesn't leak via use-after-free accesses. > > Both init_on_alloc=1 and init_on_free=1 guarantee that the allocator > returns zeroed memory. The two exceptions are slab caches with > constructors and SLAB_TYPESAFE_BY_RCU flag. Those are never > zero-initialized to preserve their semantics. > > Both init_on_alloc and init_on_free default to zero, but those defaults > can be overridden with CONFIG_INIT_ON_ALLOC_DEFAULT_ON and > CONFIG_INIT_ON_FREE_DEFAULT_ON. > > Slowdown for the new features compared to init_on_free=0, > init_on_alloc=0: > > hackbench, init_on_free=1: +7.62% sys time (st.err 0.74%) > hackbench, init_on_alloc=1: +7.75% sys time (st.err 2.14%) > > Linux build with -j12, init_on_free=1: +8.38% wall time (st.err 0.39%) > Linux build with -j12, init_on_free=1: +24.42% sys time (st.err 0.52%) > Linux build with -j12, init_on_alloc=1: -0.13% wall time (st.err 0.42%) > Linux build with -j12, init_on_alloc=1: +0.57% sys time (st.err 0.40%) > > The slowdown for init_on_free=0, init_on_alloc=0 compared to the > baseline is within the standard error. > > The new features are also going to pave the way for hardware memory > tagging (e.g. arm64's MTE), which will require both on_alloc and on_free > hooks to set the tags for heap objects. With MTE, tagging will have the > same cost as memory initialization. > > Although init_on_free is rather costly, there are paranoid use-cases where > in-memory data lifetime is desired to be minimized. There are various > arguments for/against the realism of the associated threat models, but > given that we'll need the infrastructre for MTE anyway, and there are > people who want wipe-on-free behavior no matter what the performance cost, > it seems reasonable to include it in this series. Thanks for reworking the original implemenation. This looks much better! > Signed-off-by: Alexander Potapenko <glider@xxxxxxxxxx> > Acked-by: Kees Cook <keescook@xxxxxxxxxxxx> > To: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > To: Christoph Lameter <cl@xxxxxxxxx> > To: Kees Cook <keescook@xxxxxxxxxxxx> > Cc: Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx> > Cc: Michal Hocko <mhocko@xxxxxxxxxx> > Cc: James Morris <jmorris@xxxxxxxxx> > Cc: "Serge E. Hallyn" <serge@xxxxxxxxxx> > Cc: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> > Cc: Kostya Serebryany <kcc@xxxxxxxxxx> > Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx> > Cc: Sandeep Patil <sspatil@xxxxxxxxxxx> > Cc: Laura Abbott <labbott@xxxxxxxxxx> > Cc: Randy Dunlap <rdunlap@xxxxxxxxxxxxx> > Cc: Jann Horn <jannh@xxxxxxxxxx> > Cc: Mark Rutland <mark.rutland@xxxxxxx> > Cc: Marco Elver <elver@xxxxxxxxxx> > Cc: linux-mm@xxxxxxxxx > Cc: linux-security-module@xxxxxxxxxxxxxxx > Cc: kernel-hardening@xxxxxxxxxxxxxxxxxx Acked-by: Michal Hocko <mhocko@xxxxxxx> # page allocator parts. kmalloc based parts look good to me as well but I am not sure I fill qualified to give my ack there without much more digging and I do not have much time for that now. [...] > diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c > index fd5c95ff9251..2f75dd0d0d81 100644 > --- a/kernel/kexec_core.c > +++ b/kernel/kexec_core.c > @@ -315,7 +315,7 @@ static struct page *kimage_alloc_pages(gfp_t gfp_mask, unsigned int order) > arch_kexec_post_alloc_pages(page_address(pages), count, > gfp_mask); > > - if (gfp_mask & __GFP_ZERO) > + if (want_init_on_alloc(gfp_mask)) > for (i = 0; i < count; i++) > clear_highpage(pages + i); > } I am not really sure I follow here. Why do we want to handle want_init_on_alloc here? The allocated memory comes from the page allocator and so it will get zeroed there. arch_kexec_post_alloc_pages might touch the content there but is there any actual risk of any kind of leak? > diff --git a/mm/dmapool.c b/mm/dmapool.c > index 8c94c89a6f7e..e164012d3491 100644 > --- a/mm/dmapool.c > +++ b/mm/dmapool.c > @@ -378,7 +378,7 @@ void *dma_pool_alloc(struct dma_pool *pool, gfp_t mem_flags, > #endif > spin_unlock_irqrestore(&pool->lock, flags); > > - if (mem_flags & __GFP_ZERO) > + if (want_init_on_alloc(mem_flags)) > memset(retval, 0, pool->size); > > return retval; Don't you miss dma_pool_free and want_init_on_free? -- Michal Hocko SUSE Labs
