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Re: [PATCH] arm: re-randomize rng-seed on reboot
From: |
Jason A. Donenfeld |
Subject: |
Re: [PATCH] arm: re-randomize rng-seed on reboot |
Date: |
Thu, 29 Sep 2022 22:57:22 +0200 |
Hi Peter,
On Tue, Sep 27, 2022 at 06:07:42PM +0200, Jason A. Donenfeld wrote:
> When the system reboots, the rng-seed that the FDT has should be
> re-randomized, so that the new boot gets a new seed. Since the FDT is in
> the ROM region at this point, we add a hook right after the ROM has been
> added, so that we have a pointer to that copy of the FDT. When the
> reboot happens, we then look for RNG seeds and replace their contents
> with new random data.
>
> Cc: Peter Maydell <peter.maydell@linaro.org>
> Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Just FYI, I'm waiting for your feedback on this approach, first, before
I add a similar thing for other architectures (at which point perhaps
rerandomize_fdt_seeds will be moved into device_tree.c or something).
Jason
> ---
> hw/arm/boot.c | 22 ++++++++++++++++++++++
> 1 file changed, 22 insertions(+)
>
> diff --git a/hw/arm/boot.c b/hw/arm/boot.c
> index ada2717f76..2836db4abb 100644
> --- a/hw/arm/boot.c
> +++ b/hw/arm/boot.c
> @@ -25,6 +25,7 @@
> #include "qemu/config-file.h"
> #include "qemu/option.h"
> #include "qemu/units.h"
> +#include "qemu/guest-random.h"
>
> /* Kernel boot protocol is specified in the kernel docs
> * Documentation/arm/Booting and Documentation/arm64/booting.txt
> @@ -529,6 +530,26 @@ static void fdt_add_psci_node(void *fdt)
> qemu_fdt_setprop_cell(fdt, "/psci", "migrate", migrate_fn);
> }
>
> +static void rerandomize_fdt_seeds(void *fdt)
> +{
> + int noffset, poffset, len;
> + const char *name;
> + uint8_t *data;
> +
> + for (noffset = fdt_next_node(fdt, 0, NULL);
> + noffset >= 0;
> + noffset = fdt_next_node(fdt, noffset, NULL)) {
> + for (poffset = fdt_first_property_offset(fdt, noffset);
> + poffset >= 0;
> + poffset = fdt_next_property_offset(fdt, poffset)) {
> + data = (uint8_t *)fdt_getprop_by_offset(fdt, poffset, &name,
> &len);
> + if (!data || strcmp(name, "rng-seed"))
> + continue;
> + qemu_guest_getrandom_nofail(data, len);
> + }
> + }
> +}
> +
> int arm_load_dtb(hwaddr addr, const struct arm_boot_info *binfo,
> hwaddr addr_limit, AddressSpace *as, MachineState *ms)
> {
> @@ -683,6 +704,7 @@ int arm_load_dtb(hwaddr addr, const struct arm_boot_info
> *binfo,
> * the DTB is copied again upon reset, even if addr points into RAM.
> */
> rom_add_blob_fixed_as("dtb", fdt, size, addr, as);
> + qemu_register_reset(rerandomize_fdt_seeds, rom_ptr_for_as(as, addr,
> size));
>
> g_free(fdt);
>
> --
> 2.37.3
>
>