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Date:   Wed, 29 Mar 2023 10:59:44 -0700 (PDT)
Subject:     Re: [PATCH v8 0/1] riscv: Allow to downgrade paging mode from the command line
In-Reply-To: <20230228154629.240541-1-alexghiti@rivosinc.com>
CC:     corbet@lwn.net, Paul Walmsley <paul.walmsley@sifive.com>,
        aou@eecs.berkeley.edu, Conor Dooley <conor@kernel.org>,
        Ard Biesheuvel <ardb@kernel.org>, bjorn@kernel.org,
        linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-riscv@lists.infradead.org, alexghiti@rivosinc.com
From:   Palmer Dabbelt <palmer@dabbelt.com>
To:     alexghiti@rivosinc.com
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On Tue, 28 Feb 2023 07:46:28 PST (-0800), alexghiti@rivosinc.com wrote:
> This new version gets rid of the limitation that prevented KASAN kernels
> to use the newly introduced parameters.
>
> While looking into KASLR, I fell onto commit aacd149b6238 ("arm64: head:
> avoid relocating the kernel twice for KASLR"): it allows to use the fdt
> functions very early in the boot process with KASAN enabled by simply
> compiling a new version of those functions without instrumentation.
>
> I had to change the handling of the command line parsing to make the
> code self-contained in kernel/pi/cmd_early.c to avoid calling too many
> __pi prefixed functions from outside this file.
>
> I'll use this approach like arm64 to handle the extraction of the random
> seedi from the device tree for KASLR.
>
> base-commit: eb9be8310c58 ("RISC-V: add a spin_shadow_stack declaration")

I have that in my tree, I'm still getting a bunch of boot failures 
though.  I can try to get a list if you're not seeing any, but I'm kind 
of stuck on some other stuff for a bit...

> v8:
> - Fix LLVM ld warning by moving the section .init.sdata from
>   kernel/pi/string.c into the newly created section .init.pidata
>
> v7:
> - Rebased on top of for-next which introduces lots of errors (thanks to
>   the patchwork CI)
> - Add __NO_FORTIFY to avoid undefined __pi_fortify_panic
> - Add an alias to our newly introduced strlen
> - Remove __init as sections are already prefixed in the Makefile
> - Introduce new section for kernel/pi/string.c to quiet the following
>   warnings (once we have all the string functions, we'll be able to get
>   rid of this):
>
> warning: orphan section `.init__bug_table' from `arch/riscv/kernel/pi/string.pi.o' being placed in section `.init__bug_table'
> warning: orphan section `.init.srodata.cst8' from `arch/riscv/kernel/pi/string.pi.o' being placed in section `.init.srodata.cst8'
>
> v6:
> - Fix llvm warning by forward declaring set_satp_mode_from_cmdline
>
> v5:
> - Handle null command line, Thanks Björn!
> - Add RB/TB from Björn
>
> v4:
> - Introduce pi/ for KASAN to work
>
> v3:
> - Massage commit log to make no4lvl clearer, as asked by Conor
> - Add a note to kernel-parameters.txt regarding the impossibility to use
>   those parameters when KASAN is enabled, as suggested by Conor
> - Add RB from Björn
>
> v2:
> - Honor CMDLINE_EXTEND and CMDLINE_FORCE as noticed by Björn
>
>
> Alexandre Ghiti (1):
>   riscv: Allow to downgrade paging mode from the command line
>
>  .../admin-guide/kernel-parameters.txt         |  5 +-
>  arch/riscv/kernel/Makefile                    |  2 +
>  arch/riscv/kernel/pi/Makefile                 | 37 +++++++++++
>  arch/riscv/kernel/pi/cmdline_early.c          | 62 +++++++++++++++++++
>  arch/riscv/kernel/vmlinux.lds.S               |  8 +++
>  arch/riscv/lib/memcpy.S                       |  2 +
>  arch/riscv/lib/memmove.S                      |  2 +
>  arch/riscv/lib/strlen.S                       |  1 +
>  arch/riscv/mm/init.c                          | 36 +++++++++--
>  9 files changed, 148 insertions(+), 7 deletions(-)
>  create mode 100644 arch/riscv/kernel/pi/Makefile
>  create mode 100644 arch/riscv/kernel/pi/cmdline_early.c