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

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Message-ID: <C172F31D25F5ED6E+034cc389-f02c-b681-a989-8592c5dac35e@tinylab.org>
Date:   Tue, 15 Aug 2023 19:24:18 +0800
From:   Song Shuai <songshuaishuai@...ylab.org>
To:     Alexandre Ghiti <alexghiti@...osinc.com>
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, 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?

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?


[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