[PATCH 2/5] hardening: support zeroing all malloc buffers by default

[Sascha Hauer]

On Mon, Nov 25, 2024 at 04:20:21PM +0100, Ahmad Fatoum wrote:
> dummy malloc doesn't free and all allocations are in freshly sbrk()'d
> memory, which already zero.
> 
> +config INIT_ON_ALLOC_DEFAULT_ON
> +	bool "Enable heap memory zeroing on allocation by default"
> +	depends on !MALLOC_LIBC
> +	help
> +	  This has the effect of setting "init_on_alloc=1" on the kernel
> +	  command line. This can be disabled with "init_on_alloc=0".
> +	  When "init_on_alloc" is enabled, all page allocator and slab
> +	  allocator memory will be zeroed when allocated, eliminating
> +	  many kinds of "uninitialized heap memory" flaws, especially
> +	  heap content exposures. The performance impact varies by
> +	  workload, but most cases see <1% impact. Some synthetic
> +	  workloads have measured as high as 7%.
> +
> +config INIT_ON_FREE_DEFAULT_ON
> +	bool "Enable heap memory zeroing on free by default"
> +	depends on !MALLOC_DUMMY && !MALLOC_LIBC
> +	help
> +	  This has the effect of setting "init_on_free=1" on the kernel
> +	  command line. This can be disabled with "init_on_free=0".
> +	  Similar to "init_on_alloc", when "init_on_free" is enabled,
> +	  all page allocator and slab allocator memory will be zeroed
> +	  when freed, eliminating many kinds of "uninitialized heap memory"
> +	  flaws, especially heap content exposures. The primary difference
> +	  with "init_on_free" is that data lifetime in memory is reduced,
> +	  as anything freed is wiped immediately, making live forensics or
> +	  cold boot memory attacks unable to recover freed memory contents.
> +	  The performance impact varies by workload, but is more expensive
> +	  than "init_on_alloc" due to the negative cache effects of
> +	  touching "cold" memory areas. Most cases see 3-5% impact. Some
> +	  synthetic workloads have measured as high as 8%.

These verbatim copies of the kernel help texts do not seem appropriate
for barebox.

Sascha

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