Re: [PATCH] hw/riscv: virt: pass random seed to fdt

[Alistair Francis]

On Mon, Jun 13, 2022 at 10:10 PM Jason A. Donenfeld <Jason@zx2c4.com> wrote:
>
> If the FDT contains /chosen/rng-seed, then the Linux RNG will use it to
> initialize early. Set this using the usual guest random number
> generation function. This is confirmed to successfully initialize the
> RNG on Linux 5.19-rc2.

I have a Linux 5.8 test case that is failing due to this patch.

The command line is:

qemu-system-riscv64 \
-machine virt -m 64M \
-cpu rv64,mmu=false \
-serial mon:stdio -serial null -nographic \
-append "root=/dev/vda rw highres=off  console=ttyS0 mem=1G ip=dhcp
earlycon=sbi" \
-device virtio-net-device,netdev=net0,mac=52:54:00:12:34:02 \
-netdev user,id=net0 \
-object rng-random,filename=/dev/urandom,id=rng0 \
-device virtio-rng-device,rng=rng0 \
-smp 1  \
-d guest_errors \
-kernel ./images/qemuriscv64/nommu-Image \
-drive id=disk0,file=./images/qemuriscv64/nommu-rootfs.ext2,if=none,format=raw \
-device virtio -blk-device,drive=disk0 \
-bios none

The working log (before this commit) is:

[    0.000000] Linux version 5.8.0 (alistair@risc6-mainframe)
(riscv64-elf-gcc (Arch Linux Repositories) 10.1.0, GNU ld (GNU
Binutils) 2.34) #2 SMP Wed Sep
30 12:02:11 PDT 2020
[    0.000000] earlycon: uart8250 at MMIO 0x0000000010000000 (options
'115200n8')
[    0.000000] printk: bootconsole [uart8250] enabled
[    0.000000] Zone ranges:
[    0.000000]   DMA32    [mem 0x0000000080000000-0x0000000083ffffff]
[    0.000000]   Normal   empty
[    0.000000] Movable zone start for each node
[    0.000000] Early memory node ranges
[    0.000000]   node   0: [mem 0x0000000080000000-0x0000000083ffffff]
[    0.000000] Initmem setup node 0 [mem 0x0000000080000000-0x0000000083ffffff]
[    0.000000] riscv: ISA extensions abcdefhimnrs
[    0.000000] riscv: ELF capabilities acdfim
[    0.000000] percpu: max_distance=0xc000 too large for vmalloc space 0x0
[    0.000000] percpu: Embedded 12 pages/cpu s18528 r0 d30624 u49152
[    0.000000] Built 1 zonelists, mobility grouping on.  Total pages: 16160
[    0.000000] Kernel command line: root=/dev/vda rw
earlycon=uart8250,mmio,0x10000000,115200n8 console=ttyS0
[    0.000000] Dentry cache hash table entries: 8192 (order: 4, 65536
bytes, linear)
[    0.000000] Inode-cache hash table entries: 4096 (order: 3, 32768
bytes, linear)
[    0.000000] Sorting __ex_table...
[    0.000000] mem auto-init: stack:off, heap alloc:off, heap free:off
[    0.000000] Memory: 62472K/65536K available (1369K kernel code,
144K rwdata, 238K rodata, 106K init, 134K bss, 3064K reserved, 0K
cma-reserved)
[    0.000000] rcu: Hierarchical RCU implementation.
[    0.000000] rcu:     RCU restricting CPUs from NR_CPUS=8 to nr_cpu_ids=1.
[    0.000000] rcu: RCU calculated value of scheduler-enlistment delay
is 25 jiffies.
[    0.000000] rcu: Adjusting geometry for rcu_fanout_leaf=16, nr_cpu_ids=1
[    0.000000] NR_IRQS: 64, nr_irqs: 64, preallocated irqs: 0
[    0.000000] riscv-intc: 64 local interrupts mapped
sifive_plic_read: Invalid register read 0x200c
sifive_plic_write: Invalid enable write 0x200c
[    0.000000] plic: plic@c000000: mapped 96 interrupts with 1
handlers for 2 contexts.
[    0.000000] riscv_timer_init_dt: Registering clocksource cpuid [0] hartid [0]
[    0.000000] clocksource: riscv_clocksource: mask:
0xffffffffffffffff max_cycles: 0x24e6a1710, max_idle_ns: 440795202120
ns
[    0.000106] sched_clock: 64 bits at 10MHz, resolution 100ns, wraps
every 4398046511100ns
[    0.002649] Console: colour dummy device 80x25
[    0.003599] Calibrating delay loop (skipped), value calculated
using timer frequency.. 20.00 BogoMIPS (lpj=40000)
[    0.003960] pid_max: default: 4096 minimum: 301
[    0.004718] Mount-cache hash table entries: 512 (order: 0, 4096
bytes, linear)
[    0.004922] Mountpoint-cache hash table entries: 512 (order: 0,
4096 bytes, linear)
[    0.022781] rcu: Hierarchical SRCU implementation.
[    0.024374] smp: Bringing up secondary CPUs ...
[    0.024583] smp: Brought up 1 node, 1 CPU
[    0.030450] devtmpfs: initialized
[    0.035183] clocksource: jiffies: mask: 0xffffffff max_cycles:
0xffffffff, max_idle_ns: 7645041785100000 ns
[    0.035600] futex hash table entries: 16 (order: -2, 1024 bytes, linear)
[    0.055175] clocksource: Switched to clocksource riscv_clocksource
[    0.073226] workingset: timestamp_bits=62 max_order=14 bucket_order=0
[    0.078326] Serial: 8250/16550 driver, 1 ports, IRQ sharing disabled
[    0.082509] printk: console [ttyS0] disabled
[    0.083408] 10000000.uart: ttyS0 at MMIO 0x10000000 (irq = 2,
base_baud = 230400) is a 16550A
[    0.084805] printk: console [ttyS0] enabled
[    0.084805] printk: console [ttyS0] enabled
[    0.085242] printk: bootconsole [uart8250] disabled
[    0.085242] printk: bootconsole [uart8250] disabled
virtio_mmio_write: attempt to write guest features with
guest_features_sel > 0 in legacy mode
[    0.095810] virtio_blk virtio2: [vda] 122880 512-byte logical
blocks (62.9 MB/60.0 MiB)
[    0.096155] vda: detected capacity change from 0 to 62914560
[    0.099882] random: get_random_bytes called from 0x0000000080020c8c
with crng_init=0
[    0.120690] EXT4-fs (vda): warning: mounting unchecked fs, running
e2fsck is recommended
[    0.160540] EXT4-fs (vda): mounted filesystem without journal. Opts: (null)
[    0.160910] VFS: Mounted root (ext4 filesystem) on device 254:0.
[    0.162645] devtmpfs: mounted
[    0.171902] Freeing unused kernel memory: 104K
[    0.172061] This architecture does not have kernel memory protection.
[    0.172387] Run /sbin/init as init process
[    0.174104] Run /etc/init as init process
[    0.174534] Run /bin/init as init process
[    0.174964] Run /bin/sh as init process


BusyBox v1.32.0 (2020-09-24 13:17:53 PDT) hush - the humble shell
Enter 'help' for a list of built-in commands.

After applying this commit all I see is:

Invalid read at addr 0x0, size 8, region '(null)', reason: rejected

It looks like the rng-seed property is causing failures on older kernels.

Alistair

>
> Cc: Alistair Francis <alistair.francis@wdc.com>
> Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
> ---
>  hw/riscv/virt.c | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/hw/riscv/virt.c b/hw/riscv/virt.c
> index bc424dd2f5..368a723bf6 100644
> --- a/hw/riscv/virt.c
> +++ b/hw/riscv/virt.c
> @@ -21,6 +21,7 @@
>  #include "qemu/osdep.h"
>  #include "qemu/units.h"
>  #include "qemu/error-report.h"
> +#include "qemu/guest-random.h"
>  #include "qapi/error.h"
>  #include "hw/boards.h"
>  #include "hw/loader.h"
> @@ -998,6 +999,7 @@ static void create_fdt(RISCVVirtState *s, const 
> MemMapEntry *memmap,
>      MachineState *mc = MACHINE(s);
>      uint32_t phandle = 1, irq_mmio_phandle = 1, msi_pcie_phandle = 1;
>      uint32_t irq_pcie_phandle = 1, irq_virtio_phandle = 1;
> +    uint8_t rng_seed[32];
>
>      if (mc->dtb) {
>          mc->fdt = load_device_tree(mc->dtb, &s->fdt_size);
> @@ -1046,6 +1048,10 @@ update_bootargs:
>      if (cmdline && *cmdline) {
>          qemu_fdt_setprop_string(mc->fdt, "/chosen", "bootargs", cmdline);
>      }
> +
> +    /* Pass seed to RNG. */
> +    qemu_guest_getrandom_nofail(rng_seed, sizeof(rng_seed));
> +    qemu_fdt_setprop(mc->fdt, "/chosen", "rng-seed", rng_seed, 
> sizeof(rng_seed));
>  }
>
>  static inline DeviceState *gpex_pcie_init(MemoryRegion *sys_mem,
> --
> 2.35.1
>
>