linux-kernel - Re: [PATCH] arm64: add support for rng-seed

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Date:   Fri, 10 May 2019 15:37:31 +0800
From:   Hsin-Yi Wang <hsinyi@...omium.org>
To:     Rasmus Villemoes <linux@...musvillemoes.dk>
Cc:     Rob Herring <robh+dt@...nel.org>,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        Mark Rutland <mark.rutland@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Frank Rowand <frowand.list@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Michal Hocko <mhocko@...e.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        James Morse <james.morse@....com>,
        Andrew Murray <andrew.murray@....com>,
        devicetree@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Stephen Boyd <swboyd@...omium.org>,
        Architecture Mailman List <boot-architecture@...ts.linaro.org>,
        Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH] arm64: add support for rng-seed

On Fri, May 10, 2019 at 2:14 PM Rasmus Villemoes
<linux@...musvillemoes.dk> wrote:

> So, why not just have the bootloader add whatever entropy it has via the
> commandline, which already gets mixed in? That requires no kernel
> changes, and works for all architectures.
>
> If anything, perhaps instead of just adding gobbledygook=abc123, make an
> official command line parameter (there was talk about this at some
> point), and have the kernel overwrite the value with xxx so it's not
> visible in /proc/cmdline.
>
> Rasmus

For some arch, besides commandline, we also need to overwrite bootargs
in fdt, otherwise it's still visible by
/sys/firmware/devicetree/base/chosen/bootargs for example.

Originally planned to land v2 as

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);
+
        /* break now */
        return 1;
 }

(For arm64 RW/RO issue, it will be done in other patch.)

If we add parameter into commandline, I think we probably also need to
do similar changes here since there are fdt related overwrite.