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Date: Tue, 16 Apr 2019 15:32:21 +0000
From: Christopher Lameter <cl@...ux.com>
To: Alexander Potapenko <glider@...gle.com>
cc: akpm@...ux-foundation.org, linux-security-module@...r.kernel.org, 
    linux-mm@...ck.org, ndesaulniers@...gle.com, kcc@...gle.com, 
    dvyukov@...gle.com, Kees Cook <keescook@...omium.org>, sspatil@...roid.com, 
    labbott@...hat.com, kernel-hardening@...ts.openwall.com
Subject: Re: [PATCH] mm: security: introduce CONFIG_INIT_HEAP_ALL

On Fri, 12 Apr 2019, Alexander Potapenko wrote:

> diff --git a/mm/slab.h b/mm/slab.h
> index 43ac818b8592..4bb10af0031b 100644
> --- a/mm/slab.h
> +++ b/mm/slab.h
> @@ -167,6 +167,16 @@ static inline slab_flags_t kmem_cache_flags(unsigned int object_size,
>  			      SLAB_TEMPORARY | \
>  			      SLAB_ACCOUNT)
>
> +/*
> + * Do we need to initialize this allocation?
> + * Always true for __GFP_ZERO, CONFIG_INIT_HEAP_ALL enforces initialization
> + * of caches without constructors and RCU.
> + */
> +#define SLAB_WANT_INIT(cache, gfp_flags) \
> +	((GFP_INIT_ALWAYS_ON && !(cache)->ctor && \
> +	  !((cache)->flags & SLAB_TYPESAFE_BY_RCU)) || \
> +	 (gfp_flags & __GFP_ZERO))

This is another complex thing to maintain when adding flags to the slab
allocator.

> +config INIT_HEAP_ALL
> +	bool "Initialize kernel heap allocations"

"Zero pages and objects allocated in the kernel"

> +	default n
> +	help
> +	  Enforce initialization of pages allocated from page allocator
> +	  and objects returned by kmalloc and friends.
> +	  Allocated memory is initialized with zeroes, preventing possible
> +	  information leaks and making the control-flow bugs that depend
> +	  on uninitialized values more deterministic.

Hmmm... But we already have debugging options that poison objects and
pages?

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