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Date:   Fri, 24 Feb 2023 11:02:17 +0100
From:   Alexandre Ghiti <alexghiti@...osinc.com>
To:     Jonathan Corbet <corbet@....net>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Conor Dooley <conor@...nel.org>,
        Ard Biesheuvel <ardb@...nel.org>,
        Björn Töpel <bjorn@...nel.org>,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-riscv@...ts.infradead.org
Cc:     Alexandre Ghiti <alexghiti@...osinc.com>
Subject: [PATCH v7 0/1] riscv: Allow to downgrade paging mode from the command line

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")

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               |  7 +++
 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, 147 insertions(+), 7 deletions(-)
 create mode 100644 arch/riscv/kernel/pi/Makefile
 create mode 100644 arch/riscv/kernel/pi/cmdline_early.c

-- 
2.37.2

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