[PATCH v8 0/1] riscv: Allow to downgrade paging mode from the command line

* [PATCH v8 0/1] riscv: Allow to downgrade paging mode from the command line
@ 2023-02-28 15:46 Alexandre Ghiti
  2023-02-28 15:46 ` [PATCH v8 1/1] " Alexandre Ghiti
  2023-03-29 17:59 ` [PATCH v8 0/1] " Palmer Dabbelt
  0 siblings, 2 replies; 4+ messages in thread
From: Alexandre Ghiti @ 2023-02-28 15:46 UTC (permalink / raw)
  To: Jonathan Corbet, Paul Walmsley, Palmer Dabbelt, Albert Ou,
	Conor Dooley, Ard Biesheuvel, Björn Töpel, linux-doc,
	linux-kernel, linux-riscv
  Cc: Alexandre Ghiti

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")

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

-- 
2.37.2

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