Re: [PATCH v2 0/5] LoongArch: Add kernel relocation and KASLR support

[Youling Tang]

Hi, Ruoyao

On 02/07/2023 10:28 PM, Xi Ruoyao wrote:
> This patch series to support kernel relocation and KASLR (only 64bit).
>
> I've only tested new toolchains (CONFIG_AS_HAS_EXPLICIT_RELOCS=y)
> consisted of Binutils-2.40, and GCC-12.2 heavily patched to support new
> relocs.  Unfortunately I've purged my old toolchain installation (because
> it contained a buggy GCC-12.1 miscompiling some code).  Please test the
> configuration with old toolchain.
I tested it through QEMU.

Testing in the new toolchains is successful,
/ # dmesg | head
[    0.000000] Linux version 6.2.0-rc7+ (root@bogon) 
(loongarch64-unknown-linux-gnu-gcc (GCC) 13.0.0 20220906 (experimental), 
GNU ld (GNU Binutils) 2.39.50.20220906) #67 SMP PREEMPT Wed Feb  8 
09:42:49 CST 2023
/ # cat /proc/iomem | head
00000000-0fffffff : System RAM
  00000000-002c3fff : Reserved
  002c4000-008c3fff : Reserved
  02a50000-0399ffff : Kernel code
  039a0000-0426d9ff : Kernel data
  0426da00-0439ae37 : Kernel bss


But testing in the old toolchains failed, stuck in the following
position,
[    0.000000] Linux version 6.2.0-rc7+ (root@bogon) 
(loongarch64-unknown-linux-gnu-gcc (GCC) 12.1.0, GNU ld (GNU Binutils) 
2.38.50.20220519) #68 SMP PREEMPT Wed Feb  8 09:52:49 CST 2023
...
[    0.000000] rcu: srcu_init: Setting srcu_struct sizes based on 
contention.
[    0.000000] Constant clock event device register
[    0.000000] clocksource: Constant: mask: 0xffffffffffffffff 
max_cycles: 0x171024e7e0, max_idle_ns: 440795205315 ns
[    0.000289] sched_clock: 64 bits at 100MHz, resolution 10ns, wraps 
every 4398046511100ns
[    0.000715] Constant clock source device register


In the case of "[Patch v2 2/5] LoongArch: use la.pcrel instenad of
la.abs for exception handlerS", the above failure will occur.

Patch2 may have certain problems when using the old toolchains.

Youling.

> Test results with CONFIG_RANDOMIZE_BASE=y on a 3A5000-7A2000-EVB:
>
> First boot:
>
> $ sudo cat /proc/iomem | grep Kernel
>   010e0000-018fffff : Kernel code
>   01900000-01e4b5ff : Kernel data
>   01e4b600-01f56e9f : Kernel bss
>
> Second boot:
>
> $ sudo cat /proc/iomem | grep Kernel
>   019a0000-021bffff : Kernel code
>   021c0000-0270b5ff : Kernel data
>   0270b600-02816e9f : Kernel bss
>
> Changes from v1:
>
> - Relocate the handlers instead of using a trampoline, to avoid
>   performance issue on NUMA systems.
> - Fix compiler warnings.
>
> Xi Ruoyao (2):
>   LoongArch: Use la.pcrel instead of la.abs when it's trivially possible
>   LoongArch: Use la.pcrel instead of la.abs for exception handlers
>
> Youling Tang (3):
>   LoongArch: Add JUMP_LINK_ADDR macro implementation to avoid using
>     la.abs
>   LoongArch: Add support for kernel relocation
>   LoongArch: Add support for kernel address space layout randomization
>     (KASLR)
>
>  arch/loongarch/Kconfig                  |  37 +++++
>  arch/loongarch/Makefile                 |   5 +
>  arch/loongarch/include/asm/page.h       |   6 +
>  arch/loongarch/include/asm/setup.h      |   6 +-
>  arch/loongarch/include/asm/stackframe.h |  13 +-
>  arch/loongarch/include/asm/uaccess.h    |   1 -
>  arch/loongarch/kernel/Makefile          |   2 +
>  arch/loongarch/kernel/entry.S           |   2 +-
>  arch/loongarch/kernel/genex.S           |  40 ++++-
>  arch/loongarch/kernel/head.S            |  30 +++-
>  arch/loongarch/kernel/relocate.c        | 211 ++++++++++++++++++++++++
>  arch/loongarch/kernel/setup.c           |   3 +
>  arch/loongarch/kernel/traps.c           | 138 +++++++++++++---
>  arch/loongarch/kernel/vmlinux.lds.S     |  11 +-
>  arch/loongarch/mm/tlb.c                 |  23 +--
>  arch/loongarch/mm/tlbex.S               |  72 +++++++-
>  arch/loongarch/power/suspend_asm.S      |   5 +-
>  17 files changed, 543 insertions(+), 62 deletions(-)
>  create mode 100644 arch/loongarch/kernel/relocate.c