Re: [PATCH v6 0/5] riscv: Introduce KASLR

[Sami Tolvanen]

Hi Alexandre,

On Sat, Jul 22, 2023 at 5:39 AM Alexandre Ghiti <alexghiti@xxxxxxxxxxxx> wrote:
>
> The following KASLR implementation allows to randomize the kernel mapping:
>
> - virtually: we expect the bootloader to provide a seed in the device-tree
> - physically: only implemented in the EFI stub, it relies on the firmware to
>   provide a seed using EFI_RNG_PROTOCOL. arm64 has a similar implementation
>   hence the patch 3 factorizes KASLR related functions for riscv to take
>   advantage.
>
> The new virtual kernel location is limited by the early page table that only
> has one PUD and with the PMD alignment constraint, the kernel can only take
> < 512 positions.
>
> base-commit-tag: v6.5-rc1

Thanks for continuing to work on this!

I reviewed the patches and the code looks correct to me. I also
applied the series on top of v6.5 and after patching qemu to provide a
kaslr-seed, I confirmed that the virtual offset appears to be random
and is printed out when I panic the machine:

# echo PANIC > /sys/kernel/debug/provoke-crash/DIRECT
[   17.510012] lkdtm: Performing direct entry PANIC
[   17.510411] Kernel panic - not syncing: dumptest
[...]
[   17.518693] Kernel Offset: 0x32c00000 from 0xffffffff80000000

For the series:
Reviewed-by: Sami Tolvanen <samitolvanen@xxxxxxxxxx>

I didn't test the EFI bits, but the rest of the series:
Tested-by: Sami Tolvanen <samitolvanen@xxxxxxxxxx>

Conor, in another reply you mentioned you're planning on reviewing the
patches as well. Did you have any feedback or concerns?

Sami