linux-kernel - Re: [PATCH v2 1/2] fdt: add support for rng-seed

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Date:   Mon, 13 May 2019 11:42:02 +0300
From:   Mike Rapoport <rppt@...ux.ibm.com>
To:     Hsin-Yi Wang <hsinyi@...omium.org>
Cc:     linux-arm-kernel@...ts.infradead.org,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Frank Rowand <frowand.list@...il.com>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        Stephen Boyd <swboyd@...omium.org>,
        Kees Cook <keescook@...omium.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        boot-architecture@...ts.linaro.org,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Miles Chen <miles.chen@...iatek.com>,
        James Morse <james.morse@....com>,
        Andrew Murray <andrew.murray@....com>
Subject: Re: [PATCH v2 1/2] fdt: add support for rng-seed

On Mon, May 13, 2019 at 08:38:18AM +0800, Hsin-Yi Wang wrote:
> Introducing a chosen node, rng-seed, which is an entropy that can be
> passed to kernel called very early to increase initial device
> randomness. Bootloader should provide this entropy and the value is
> read from /chosen/rng-seed in DT.
> 
> Signed-off-by: Hsin-Yi Wang <hsinyi@...omium.org>
> ---
> change log:
> v1->v2:
> * call function in early_init_dt_scan_chosen
> * will add doc to devicetree-org/dt-schema on github if this is accepted
> ---
>  Documentation/devicetree/bindings/chosen.txt | 14 ++++++++++++++
>  drivers/of/fdt.c                             | 11 +++++++++++
>  2 files changed, 25 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/chosen.txt b/Documentation/devicetree/bindings/chosen.txt
> index 45e79172a646..fef5c82672dc 100644
> --- a/Documentation/devicetree/bindings/chosen.txt
> +++ b/Documentation/devicetree/bindings/chosen.txt
> @@ -28,6 +28,20 @@ mode) when EFI_RNG_PROTOCOL is supported, it will be overwritten by
>  the Linux EFI stub (which will populate the property itself, using
>  EFI_RNG_PROTOCOL).
>  
> +rng-seed
> +-----------
> +
> +This property served as an entropy to add device randomness. It is parsed
> +as a byte array, e.g.
> +
> +/ {
> +	chosen {
> +		rng-seed = <0x31 0x95 0x1b 0x3c 0xc9 0xfa 0xb3 ...>;
> +	};
> +};
> +
> +This random value should be provided by bootloader.
> +
>  stdout-path
>  -----------
>  
> diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
> index de893c9616a1..96ea5eba9dd5 100644
> --- a/drivers/of/fdt.c
> +++ b/drivers/of/fdt.c
> @@ -24,6 +24,7 @@
>  #include <linux/debugfs.h>
>  #include <linux/serial_core.h>
>  #include <linux/sysfs.h>
> +#include <linux/random.h>
>  
>  #include <asm/setup.h>  /* for COMMAND_LINE_SIZE */
>  #include <asm/page.h>
> @@ -1079,6 +1080,7 @@ int __init early_init_dt_scan_chosen(unsigned long node, const char *uname,
>  {
>  	int l;
>  	const char *p;
> +	const void *rng_seed;
>  
>  	pr_debug("search \"chosen\", depth: %d, uname: %s\n", depth, uname);
>  
> @@ -1113,6 +1115,15 @@ int __init early_init_dt_scan_chosen(unsigned long node, const char *uname,
>  
>  	pr_debug("Command line is: %s\n", (char*)data);
>  
> +	rng_seed = of_get_flat_dt_prop(node, "rng-seed", &l);
> +	if (!rng_seed || l == 0)
> +		return 1;
> +
> +	/* try to clear seed so it won't be found. */
> +        fdt_nop_property(initial_boot_params, node, "rng-seed");
> +
> +        add_device_randomness(rng_seed, l);

Please fix the indentation. 

> +
>  	/* break now */
>  	return 1;
>  }
> -- 
> 2.20.1
> 

-- 
Sincerely yours,
Mike.