Re: [PATCH v4 09/11] mips/malta: pass RNG seed via env var and re-randomize on reboot
On Tue, 25 Oct 2022 at 01:44, Jason A. Donenfeld wrote:
>
> As of the kernel commit linked below, Linux ingests an RNG seed
> passed as part of the environment block by the bootloader or firmware.
> This mechanism works across all different environment block types,
> generically, which pass some block via the second firmware argument. On
> malta, this has been tested to work when passed as an argument from
> U-Boot's linux_env_set.
>
> As is the case on most other architectures (such as boston), when
> booting with `-kernel`, QEMU, acting as the bootloader, should pass the
> RNG seed, so that the machine has good entropy for Linux to consume. So
> this commit implements that quite simply by using the guest random API,
> which is what is used on nearly all other archs too. It also
> reinitializes the seed on reboot, so that it is always fresh.
>
> Link: https://git.kernel.org/torvalds/c/056a68cea01
> Cc: Aleksandar Rikalo
> Cc: Paul Burton
> Cc: Philippe Mathieu-Daudé
> Signed-off-by: Jason A. Donenfeld
> ---
> hw/mips/malta.c | 25 +
> 1 file changed, 25 insertions(+)
>
> diff --git a/hw/mips/malta.c b/hw/mips/malta.c
> index 0e932988e0..d337de920c 100644
> --- a/hw/mips/malta.c
> +++ b/hw/mips/malta.c
> @@ -26,6 +26,7 @@
> #include "qemu/units.h"
> #include "qemu/bitops.h"
> #include "qemu/datadir.h"
> +#include "qemu/guest-random.h"
> #include "hw/clock.h"
> #include "hw/southbridge/piix.h"
> #include "hw/isa/superio.h"
> @@ -1017,6 +1018,17 @@ static void G_GNUC_PRINTF(3, 4) prom_set(uint32_t
> *prom_buf, int index,
> va_end(ap);
> }
>
> +static void reinitialize_rng_seed(void *opaque)
> +{
> +char *rng_seed_hex = opaque;
> +uint8_t rng_seed[32];
> +
> +qemu_guest_getrandom_nofail(rng_seed, sizeof(rng_seed));
> +for (size_t i = 0; i < sizeof(rng_seed); ++i) {
> +sprintf(rng_seed_hex + i * 2, "%02x", rng_seed[i]);
> +}
> +}
> +
> /* Kernel */
> static uint64_t load_kernel(void)
> {
> @@ -1028,6 +1040,8 @@ static uint64_t load_kernel(void)
> long prom_size;
> int prom_index = 0;
> uint64_t (*xlate_to_kseg0) (void *opaque, uint64_t addr);
> +uint8_t rng_seed[32];
> +char rng_seed_hex[sizeof(rng_seed) * 2 + 1];
>
> #if TARGET_BIG_ENDIAN
> big_endian = 1;
> @@ -1115,9 +1129,20 @@ static uint64_t load_kernel(void)
>
> prom_set(prom_buf, prom_index++, "modetty0");
> prom_set(prom_buf, prom_index++, "38400n8r");
> +
> +qemu_guest_getrandom_nofail(rng_seed, sizeof(rng_seed));
> +for (size_t i = 0; i < sizeof(rng_seed); ++i) {
> +sprintf(rng_seed_hex + i * 2, "%02x", rng_seed[i]);
> +}
> +prom_set(prom_buf, prom_index++, "rngseed");
> +prom_set(prom_buf, prom_index++, "%s", rng_seed_hex);
> +
> prom_set(prom_buf, prom_index++, NULL);
>
> rom_add_blob_fixed("prom", prom_buf, prom_size, ENVP_PADDR);
> +qemu_register_reset_nosnapshotload(reinitialize_rng_seed,
> +memmem(rom_ptr(ENVP_PADDR, prom_size), prom_size,
> + rng_seed_hex, sizeof(rng_seed_hex)));
So I didn't take this one patch, partly because I don't think
all our supported build platforms have memmem(), and partly
because when I then looked a bit closer at it it looks like
we're searching through the whole blob for the RNG
seed. We know where it is to start with, so I think it would
be cleaner to have prom_set return table_addr (ie the offset
into the blob of what it just wrote) so we can use it here.
(You could also reverse-engineer it from prom_buf[prom_index - 1]
but returning the offset seems a bit less awkward.)
thanks
-- PMM
Re: [PATCH v4 09/11] mips/malta: pass RNG seed via env var and re-randomize on reboot
Hi Peter, On Tue, Oct 25, 2022 at 6:47 PM Peter Maydell wrote: > So I didn't take this one patch, partly because I don't think No problem - I'm actually quite happy to finally have this one reviewed. I'll send you a follow up. > all our supported build platforms have memmem(), and partly > because when I then looked a bit closer at it it looks like > we're searching through the whole blob for the RNG > seed. We know where it is to start with, so I think it would > be cleaner to have prom_set return table_addr (ie the offset > into the blob of what it just wrote) so we can use it here. > (You could also reverse-engineer it from prom_buf[prom_index - 1] > but returning the offset seems a bit less awkward.) You're right that the memmem is a bit lazy. I'll sort out a more direct way of doing it like I do for the other platforms. Jason
[PATCH v4 09/11] mips/malta: pass RNG seed via env var and re-randomize on reboot
As of the kernel commit linked below, Linux ingests an RNG seed
passed as part of the environment block by the bootloader or firmware.
This mechanism works across all different environment block types,
generically, which pass some block via the second firmware argument. On
malta, this has been tested to work when passed as an argument from
U-Boot's linux_env_set.
As is the case on most other architectures (such as boston), when
booting with `-kernel`, QEMU, acting as the bootloader, should pass the
RNG seed, so that the machine has good entropy for Linux to consume. So
this commit implements that quite simply by using the guest random API,
which is what is used on nearly all other archs too. It also
reinitializes the seed on reboot, so that it is always fresh.
Link: https://git.kernel.org/torvalds/c/056a68cea01
Cc: Aleksandar Rikalo
Cc: Paul Burton
Cc: Philippe Mathieu-Daudé
Signed-off-by: Jason A. Donenfeld
---
hw/mips/malta.c | 25 +
1 file changed, 25 insertions(+)
diff --git a/hw/mips/malta.c b/hw/mips/malta.c
index 0e932988e0..d337de920c 100644
--- a/hw/mips/malta.c
+++ b/hw/mips/malta.c
@@ -26,6 +26,7 @@
#include "qemu/units.h"
#include "qemu/bitops.h"
#include "qemu/datadir.h"
+#include "qemu/guest-random.h"
#include "hw/clock.h"
#include "hw/southbridge/piix.h"
#include "hw/isa/superio.h"
@@ -1017,6 +1018,17 @@ static void G_GNUC_PRINTF(3, 4) prom_set(uint32_t
*prom_buf, int index,
va_end(ap);
}
+static void reinitialize_rng_seed(void *opaque)
+{
+char *rng_seed_hex = opaque;
+uint8_t rng_seed[32];
+
+qemu_guest_getrandom_nofail(rng_seed, sizeof(rng_seed));
+for (size_t i = 0; i < sizeof(rng_seed); ++i) {
+sprintf(rng_seed_hex + i * 2, "%02x", rng_seed[i]);
+}
+}
+
/* Kernel */
static uint64_t load_kernel(void)
{
@@ -1028,6 +1040,8 @@ static uint64_t load_kernel(void)
long prom_size;
int prom_index = 0;
uint64_t (*xlate_to_kseg0) (void *opaque, uint64_t addr);
+uint8_t rng_seed[32];
+char rng_seed_hex[sizeof(rng_seed) * 2 + 1];
#if TARGET_BIG_ENDIAN
big_endian = 1;
@@ -1115,9 +1129,20 @@ static uint64_t load_kernel(void)
prom_set(prom_buf, prom_index++, "modetty0");
prom_set(prom_buf, prom_index++, "38400n8r");
+
+qemu_guest_getrandom_nofail(rng_seed, sizeof(rng_seed));
+for (size_t i = 0; i < sizeof(rng_seed); ++i) {
+sprintf(rng_seed_hex + i * 2, "%02x", rng_seed[i]);
+}
+prom_set(prom_buf, prom_index++, "rngseed");
+prom_set(prom_buf, prom_index++, "%s", rng_seed_hex);
+
prom_set(prom_buf, prom_index++, NULL);
rom_add_blob_fixed("prom", prom_buf, prom_size, ENVP_PADDR);
+qemu_register_reset_nosnapshotload(reinitialize_rng_seed,
+memmem(rom_ptr(ENVP_PADDR, prom_size), prom_size,
+ rng_seed_hex, sizeof(rng_seed_hex)));
g_free(prom_buf);
return kernel_entry;
--
2.38.1
