linux-kernel - Re: [PATCH v14 5/5] x86/boot/KASLR: Limit KASLR to extracting kernel in immovable memory

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Date:   Mon, 17 Dec 2018 18:43:24 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Chao Fan <fanc.fnst@...fujitsu.com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org, bp@...en8.de,
        tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
        keescook@...omium.org, bhe@...hat.com, msys.mizuma@...il.com,
        indou.takao@...fujitsu.com, caoj.fnst@...fujitsu.com
Subject: Re: [PATCH v14 5/5] x86/boot/KASLR: Limit KASLR to extracting kernel
 in immovable memory


* Chao Fan <fanc.fnst@...fujitsu.com> wrote:

> KASLR randomly chooses some positions which may locate in movable
> memory regions. It will break memory hotplug feature and make the
> movable memory chosen by KASLR practically immovable.
> 
> The solution is to limit KASLR to choose memory regions in immovable
> node according to SRAT tables.
> When CONFIG_EARLY_PARSE_RSDP is enabled, walk through SRAT to get the
> information of immovable memory so that KASLR knows where should be
> chosen for randomization.
> 
> Rename process_mem_region() as __process_mem_region() and name new
> function as process_mem_region().
> 
> Signed-off-by: Chao Fan <fanc.fnst@...fujitsu.com>
> ---
>  arch/x86/boot/compressed/kaslr.c | 75 +++++++++++++++++++++++++++-----
>  1 file changed, 64 insertions(+), 11 deletions(-)

Ok, I like this basic approach of automatically detecing memory areas we 
should not KASLR into - it's far better than earlier iterations.

> +++ b/arch/x86/boot/compressed/kaslr.c
> @@ -97,6 +97,11 @@ static bool memmap_too_large;
>  /* Store memory limit specified by "mem=nn[KMG]" or "memmap=nn[KMG]" */
>  static unsigned long long mem_limit = ULLONG_MAX;
>  
> +#ifdef CONFIG_EARLY_SRAT_PARSE
> +/* The immovable memory regions */
> +extern struct mem_vector immovable_mem[MAX_NUMNODES*2];
> +#endif

What logic is the maximum size of this array based on?

Thanks,

	Ingo