Hi Jason,
On Fri, Sep 30, 2022 at 4:05 PM Jason A. Donenfeld <Jason@xxxxxxxxx> wrote:
>
> Nearly all other firmware environments have some way of passing a RNG
> seed to initialize the RNG: DTB's rng-seed, EFI's RNG protocol, m68k's
> bootinfo block, x86's setup_data, and so forth. This adds something
> similar for MIPS, which will allow various firmware environments,
> bootloaders, and hypervisors to pass an RNG seed to initialize the
> kernel's RNG.
>
> Signed-off-by: Jason A. Donenfeld <Jason@xxxxxxxxx>
> ---
> arch/mips/kernel/setup.c | 21 +++++++++++++++++++++
> 1 file changed, 21 insertions(+)
>
> diff --git a/arch/mips/kernel/setup.c b/arch/mips/kernel/setup.c
> index 2ca156a5b231..39c79f67c7a3 100644
> --- a/arch/mips/kernel/setup.c
> +++ b/arch/mips/kernel/setup.c
> @@ -42,6 +42,7 @@
> #include <asm/setup.h>
> #include <asm/smp-ops.h>
> #include <asm/prom.h>
> +#include <asm/fw/fw.h>
>
> #ifdef CONFIG_MIPS_ELF_APPENDED_DTB
> char __section(".appended_dtb") __appended_dtb[0x100000];
> @@ -756,6 +757,24 @@ static void __init prefill_possible_map(void)
> static inline void prefill_possible_map(void) {}
> #endif
>
> +static void __init setup_rng_seed(void)
> +{
> + char *rng_seed_hex = fw_getenv("rngseed");
> + u8 rng_seed[512];
> + size_t len;
> +
> + if (!rng_seed_hex)
> + return;
> +
Assuming rngseed="x", ...
> + len = min(sizeof(rng_seed), strlen(rng_seed_hex) / 2);
... len = 0 ...
> + if (hex2bin(rng_seed, rng_seed_hex, len))
> + return;
hex2bin(..., len=0) = 0
> +
> + add_bootloader_randomness(rng_seed, len);
So we call char/random code with len=0. Is it safe?
Maybe simply safer to check len before calling hex2bin?
> + memzero_explicit(rng_seed, len);
> + memzero_explicit(rng_seed_hex, len * 2);
> +}
> +
> void __init setup_arch(char **cmdline_p)
> {
> cpu_probe();
> @@ -786,6 +805,8 @@ void __init setup_arch(char **cmdline_p)
> paging_init();
>
> memblock_dump_all();
> +
> + setup_rng_seed();
> }
>
> unsigned long kernelsp[NR_CPUS];
> --
> 2.37.3
>
