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

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Message-ID: <CAHVXubhD2r2OYQKRcBUfA+3h4SdejkUhVDD2Gx6WJ6pqBzSKpw@mail.gmail.com>
Date:   Thu, 17 Aug 2023 15:10:30 +0200
From:   Alexandre Ghiti <alexghiti@...osinc.com>
To:     Song Shuai <songshuaishuai@...ylab.org>
Cc:     Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-efi@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Albert Ou <aou@...s.berkeley.edu>, zong.li@...ive.com,
        conor.dooley@...rochip.com
Subject: Re: [PATCH v6 0/5] riscv: Introduce KASLR

Hi Song,

On Tue, Aug 15, 2023 at 1:24 PM Song Shuai <songshuaishuai@...ylab.org> wrote:
>
>
> Hi, Alex:
>
> 在 2023/7/22 20:38, Alexandre Ghiti 写道:
> > 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.
> >
>
> I have gone through the code and tested this series with RiscVVirt edk2.
> All seems good to me, you can add :
>
> Tested-by: Song Shuai <songshuaishuai@...ylab.org>
>
> And a few questions about patch 2 ("riscv: Dump out kernel offset
> information on panic"):
>
> 1. The dump_kernel_offset() function would output "Kernel Offset: 0x0
> from 0xffffffff80000000" when booting with "nokaslr" option.
>
> How about disabling the registration of "kernel_offset_notifier" with
> "nokaslr" option?

I'd rather keep it as it shows the "nokaslr" flag was taken into account.

>
> 2. Inspired by patch 2, I added the Crash KASLR support based on this
> series [1].
> So is it necessary to keep this patch if we have Crash KASLR support?

I don't understand your question here

>
>
> [1]:
> https://lore.kernel.org/linux-riscv/20230815104800.705753-1-songshuaishuai@tinylab.org/T/#u
>
> > base-commit-tag: v6.5-rc1
> >
> > Changes in v6:
> >    * Fix reintroduced build failures by compiling kaslr.c only for arm64
> >      and riscv, as suggested by Ard
> >
> > Changes in v5:
> >    * Renamed efi-stub-kaslr.c into kaslr.c and fix commit log of patch 3,
> >      as suggested by Ard
> >    * Removed stubs since the kaslr functions were moved to their own file
> >      (and then does not trigger any build failure for architectures that do
> >      not call those functions since they are in their own compilation unit)
> >
> > Changes in v4:
> >    * Fix efi_get_kimg macro that returned nothing
> >    * Moved new kaslr functions into their own files to avoid zboot link
> >      failures, as suggested by Ard
> >
> > Changes in v3:
> >    * Rebase on top of 6.4-rc2
> >    * Make RANDOMIZE_BASE depend on 64bit
> >    * Fix efi_icache_sync and efi_get_kimg_min_align which were undefined
> >      in x86 (and certainly other archs)
> >    * Add patch 4 to fix warning on rv32
> >
> > Changes in v2:
> >    * Rebase on top of 6.3-rc1
> >    * Add a riscv cache sync after memcpying the kernel
> >    * Add kaslr_offset implementation for KCOV
> >    * Add forward declaration to quiet LLVM
> >
> > Alexandre Ghiti (5):
> >    riscv: Introduce virtual kernel mapping KASLR
> >    riscv: Dump out kernel offset information on panic
> >    arm64: libstub: Move KASLR handling functions to kaslr.c
> >    libstub: Fix compilation warning for rv32
> >    riscv: libstub: Implement KASLR by using generic functions
> >
> >   arch/arm64/include/asm/efi.h              |   2 +
> >   arch/riscv/Kconfig                        |  19 +++
> >   arch/riscv/include/asm/efi.h              |   2 +
> >   arch/riscv/include/asm/page.h             |   3 +
> >   arch/riscv/kernel/image-vars.h            |   1 +
> >   arch/riscv/kernel/pi/Makefile             |   2 +-
> >   arch/riscv/kernel/pi/cmdline_early.c      |  13 ++
> >   arch/riscv/kernel/pi/fdt_early.c          |  30 ++++
> >   arch/riscv/kernel/setup.c                 |  25 ++++
> >   arch/riscv/mm/init.c                      |  36 ++++-
> >   drivers/firmware/efi/libstub/Makefile     |   4 +-
> >   drivers/firmware/efi/libstub/arm64-stub.c | 117 ++--------------
> >   drivers/firmware/efi/libstub/efistub.h    |   8 ++
> >   drivers/firmware/efi/libstub/kaslr.c      | 159 ++++++++++++++++++++++
> >   drivers/firmware/efi/libstub/riscv-stub.c |  33 ++---
> >   15 files changed, 328 insertions(+), 126 deletions(-)
> >   create mode 100644 arch/riscv/kernel/pi/fdt_early.c
> >   create mode 100644 drivers/firmware/efi/libstub/kaslr.c
> >
>
> --
> Thanks
> Song Shuai

Thanks for testing this and your suggestions!

Alex