[PATCH v5 2/5] fdt: kaslr seed from RNG device

[Simon Glass]

Hi Sean,

On Thu, 16 Nov 2023 at 19:02, <seanedmond at linux.microsoft.com> wrote:
>
> From: Dhananjay Phadke <dphadke at linux.microsoft.com>
>
> Add support for KASLR seed from the RNG device. Invokes dm_rng_read()
> API to read 8-bytes of random bytes.  Performs the FDT fixup using event
> spy.  To enable use CONFIG_KASLR_RNG_SEED
>
> Signed-off-by: Dhananjay Phadke <dphadke at linux.microsoft.com>
> Signed-off-by: Drew Kluemke <ankluemk at microsoft.com>
> Signed-off-by: Sean Edmond <seanedmond at microsoft.com>
> ---
>  boot/fdt_support.c | 36 ++++++++++++++++++++++++++++++++++++
>  lib/Kconfig        |  7 +++++++
>  2 files changed, 43 insertions(+)
>

Reviewed-by: Simon Glass <sjg at chromium.org>

> diff --git a/boot/fdt_support.c b/boot/fdt_support.c
> index 49d14a949be..12defcf645c 100644
> --- a/boot/fdt_support.c
> +++ b/boot/fdt_support.c
> @@ -12,7 +12,10 @@
>  #include <log.h>
>  #include <mapmem.h>
>  #include <net.h>
> +#include <rng.h>
>  #include <stdio_dev.h>
> +#include <dm/device.h>
> +#include <dm/uclass.h>
>  #include <dm/ofnode.h>
>  #include <linux/ctype.h>
>  #include <linux/types.h>
> @@ -650,6 +653,39 @@ int fdt_fixup_kaslr_seed(ofnode node, const u8 *seed, int len)
>         return 0;
>  }
>
> +int fdt_rng_kaslr_seed(void *ctx, struct event *event)
> +{
> +       u8 rand[8] = {0};
> +       struct udevice *dev;
> +       int ret;
> +       oftree tree = event->data.ft_fixup.tree;
> +       ofnode root_node = oftree_root(tree);
> +
> +       ret = uclass_first_device_err(UCLASS_RNG, &dev);
> +       if (ret) {
> +               printf("ERROR: Failed to find RNG device\n");
> +               return ret;
> +       }
> +
> +       ret = dm_rng_read(dev, rand, sizeof(rand));
> +       if (ret) {
> +               printf("ERROR: RNG read failed, ret=%d\n", ret);
> +               return ret;
> +       }
> +
> +       ret = fdt_fixup_kaslr_seed(root_node, rand, sizeof(rand));
> +       if (ret) {
> +               printf("ERROR: failed to add kaslr-seed to fdt\n");
> +               return ret;
> +       }
> +
> +       return 0;
> +}
> +
> +#if defined(CONFIG_KASLR_RNG_SEED)

You could put this if() in the function above


> +EVENT_SPY(EVT_FT_FIXUP, fdt_rng_kaslr_seed);
> +#endif
> +
>  int fdt_record_loadable(void *blob, u32 index, const char *name,
>                         uintptr_t load_addr, u32 size, uintptr_t entry_point,
>                         const char *type, const char *os, const char *arch)
> diff --git a/lib/Kconfig b/lib/Kconfig
> index 19649517a39..4f5dfc00d6f 100644
> --- a/lib/Kconfig
> +++ b/lib/Kconfig
> @@ -477,6 +477,13 @@ config VPL_TPM
>           for the low-level TPM interface, but only one TPM is supported at
>           a time by the TPM library.
>
> +config KASLR_RNG_SEED
> +       bool "Use RNG driver for KASLR random seed"
> +       depends on DM_RNG
> +       help
> +         This enables support for using the RNG driver as entropy source for
> +         KASLR seed populated in kernel's device tree.
> +
>  endmenu
>
>  menu "Android Verified Boot"
> --
> 2.42.0
>