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

[Ahmad Fatoum]

On 28.11.24 10:08, Sascha Hauer wrote:
> 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.

Agreed. I was intending to change them, but forgot about it :/

Will fix in v2.

> 
> Sascha
> 


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