Re: [PATCH v7 1/2] mm: security: introduce init_on_alloc=1 and init_on_free=1 boot options

[Qian Cai <cai@lca.pw>]

On Fri, 2019-06-21 at 15:31 +0200, Alexander Potapenko wrote:
> On Fri, Jun 21, 2019 at 2:36 PM Qian Cai <cai@lca.pw> wrote:
> > 
> > On Mon, 2019-06-17 at 17:10 +0200, Alexander Potapenko wrote:
> > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > > index d66bc8abe0af..50a3b104a491 100644
> > > --- a/mm/page_alloc.c
> > > +++ b/mm/page_alloc.c
> > > @@ -136,6 +136,48 @@ unsigned long totalcma_pages __read_mostly;
> > > 
> > >  int percpu_pagelist_fraction;
> > >  gfp_t gfp_allowed_mask __read_mostly = GFP_BOOT_MASK;
> > > +#ifdef CONFIG_INIT_ON_ALLOC_DEFAULT_ON
> > > +DEFINE_STATIC_KEY_TRUE(init_on_alloc);
> > > +#else
> > > +DEFINE_STATIC_KEY_FALSE(init_on_alloc);
> > > +#endif
> > > +#ifdef CONFIG_INIT_ON_FREE_DEFAULT_ON
> > > +DEFINE_STATIC_KEY_TRUE(init_on_free);
> > > +#else
> > > +DEFINE_STATIC_KEY_FALSE(init_on_free);
> > > +#endif
> > > +
> > 
> > There is a problem here running kernels built with clang,
> > 
> > [    0.000000] static_key_disable(): static key 'init_on_free+0x0/0x4' used
> > before call to jump_label_init()
> > [    0.000000] WARNING: CPU: 0 PID: 0 at ./include/linux/jump_label.h:314
> > early_init_on_free+0x1c0/0x200
> > [    0.000000] Modules linked in:
> > [    0.000000] CPU: 0 PID: 0 Comm: swapper Not tainted 5.2.0-rc5-next-
> > 20190620+
> > #11
> > [    0.000000] pstate: 60000089 (nZCv daIf -PAN -UAO)
> > [    0.000000] pc : early_init_on_free+0x1c0/0x200
> > [    0.000000] lr : early_init_on_free+0x1c0/0x200
> > [    0.000000] sp : ffff100012c07df0
> > [    0.000000] x29: ffff100012c07e20 x28: ffff1000110a01ec
> > [    0.000000] x27: 0000000000000001 x26: ffff100011716f88
> > [    0.000000] x25: ffff100010d367ae x24: ffff100010d367a5
> > [    0.000000] x23: ffff100010d36afd x22: ffff100011716758
> > [    0.000000] x21: 0000000000000000 x20: 0000000000000000
> > [    0.000000] x19: 0000000000000000 x18: 000000000000002e
> > [    0.000000] x17: 000000000000000f x16: 0000000000000040
> > [    0.000000] x15: 0000000000000000 x14: 6d756a206f74206c
> > [    0.000000] x13: 6c61632065726f66 x12: 6562206465737520
> > [    0.000000] x11: 0000000000000000 x10: 0000000000000000
> > [    0.000000] x9 : 0000000000000000 x8 : 0000000000000000
> > [    0.000000] x7 : 73203a2928656c62 x6 : ffff1000144367ad
> > [    0.000000] x5 : ffff100012c07b28 x4 : 000000000000000f
> > [    0.000000] x3 : ffff1000101b36ec x2 : 0000000000000001
> > [    0.000000] x1 : 0000000000000001 x0 : 000000000000005d
> > [    0.000000] Call trace:
> > [    0.000000]  early_init_on_free+0x1c0/0x200
> > [    0.000000]  do_early_param+0xd0/0x104
> > [    0.000000]  parse_args+0x204/0x54c
> > [    0.000000]  parse_early_param+0x70/0x8c
> > [    0.000000]  setup_arch+0xa8/0x268
> > [    0.000000]  start_kernel+0x80/0x588
> > [    0.000000] random: get_random_bytes called from __warn+0x164/0x208 with
> > crng_init=0
> > 
> > > diff --git a/mm/slub.c b/mm/slub.c
> > > index cd04dbd2b5d0..9c4a8b9a955c 100644
> > > --- a/mm/slub.c
> > > +++ b/mm/slub.c
> > > @@ -1279,6 +1279,12 @@ static int __init setup_slub_debug(char *str)
> > >       if (*str == ',')
> > >               slub_debug_slabs = str + 1;
> > >  out:
> > > +     if ((static_branch_unlikely(&init_on_alloc) ||
> > > +          static_branch_unlikely(&init_on_free)) &&
> > > +         (slub_debug & SLAB_POISON)) {
> > > +             pr_warn("disabling SLAB_POISON: can't be used together with
> > > memory auto-initialization\n");
> > > +             slub_debug &= ~SLAB_POISON;
> > > +     }
> > >       return 1;
> > >  }
> > 
> > I don't think it is good idea to disable SLAB_POISON here as if people have
> > decided to enable SLUB_DEBUG later already, they probably care more to make
> > sure
> > those additional checks with SLAB_POISON are still running to catch memory
> > corruption.
> 
> The problem is that freed buffers can't be both poisoned and zeroed at
> the same time.
> Do you think we need to disable memory initialization in that case instead?

Yes, disable init_on_free|alloc and keep SLAB_POISON sounds good to me.