linux-kernel - Re: [PATCH 0/4] riscv: Introduce KASLR

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Message-ID: <878rgrqapf.fsf@all.your.base.are.belong.to.us>
Date:   Tue, 21 Feb 2023 16:50:36 +0100
From:   Björn Töpel <bjorn@...nel.org>
To:     Alexandre Ghiti <alexghiti@...osinc.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Ard Biesheuvel <ardb@...nel.org>,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-efi@...r.kernel.org
Cc:     Alexandre Ghiti <alexghiti@...osinc.com>
Subject: Re: [PATCH 0/4] riscv: Introduce KASLR

Alexandre Ghiti <alexghiti@...osinc.com> writes:

> 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.
>
> Note that the patch "riscv: Use PUD/P4D/PGD pages for the linear
> mapping" is necessary to retrieve the memory below the physical kernel
> address, so that the EFI stub does not have to try to relocate the kernel
> as close as possible to the start of dram.
>
> This patchset is rebased on top of:
>
> Introduce 64b relocatable kernel (https://lore.kernel.org/lkml/20230215143626.453491-1-alexghiti@rivosinc.com/)
> RISC-V kasan rework (https://lore.kernel.org/lkml/Y6TTvku%2FyuSjm42j@spud/T/)
> riscv: Use PUD/P4D/PGD pages for the linear mapping (https://lore.kernel.org/lkml/20230125114229.hrhsyw4aegrnmoau@orel/T/)
> riscv: Allow to downgrade paging mode from the command line (https://lore.kernel.org/lkml/CAHVXubjeSMvfTPnvrnYRupOGx6+vUvUGfRS3piTeo=TH2cHKNg@mail.gmail.com/)
> base-commit-tag: v6.2-rc7
>
> This patchset was tested with u-boot boottime service for the seed on:
> - ubuntu defconfig + kasan outline (sv39, sv48, sv57): OK
> - ubuntu defconfig + kasan inline (sv39, sv48, sv57): OK
> - ubuntu defconfg (sv39, sv48, sv57): OK

I've taken the series for a spin (qemu u-boot UEFI, and qemu non-UEFI),
on-top of the patches outline above, but with 6.2 proper.

For the series:
Reviewed-by: Björn Töpel <bjorn@...osinc.com>
Tested-by: Björn Töpel <bjorn@...osinc.com>