Re: [RFC][PATCH 1/4] module: mm: Make module_alloc() generally available

[Christophe Leroy]

Hi Calvin,

Le 06/03/2024 à 21:05, Calvin Owens a écrit :
> [Vous ne recevez pas souvent de courriers de jcalvinowens@xxxxxxxxx. Découvrez pourquoi ceci est important à https://aka.ms/LearnAboutSenderIdentification ]
> 
> Both BPF_JIT and KPROBES depend on CONFIG_MODULES, but only require
> module_alloc() itself, which can be easily separated into a standalone
> allocator for executable kernel memory.

Easily maybe, but not as easily as you think, see below.

> 
> Thomas Gleixner sent a patch to do that for x86 as part of a larger
> series a couple years ago:
> 
>      https://lore.kernel.org/all/20220716230953.442937066@xxxxxxxxxxxxx/
> 
> I've simply extended that approach to the whole kernel.
> 
> Signed-off-by: Calvin Owens <jcalvinowens@xxxxxxxxx>
> ---
>   arch/Kconfig                     |   2 +-
>   arch/arm/kernel/module.c         |  35 ---------
>   arch/arm/mm/Makefile             |   2 +
>   arch/arm/mm/module_alloc.c       |  40 ++++++++++
>   arch/arm64/kernel/module.c       | 127 ------------------------------
>   arch/arm64/mm/Makefile           |   1 +
>   arch/arm64/mm/module_alloc.c     | 130 +++++++++++++++++++++++++++++++
>   arch/loongarch/kernel/module.c   |   6 --
>   arch/loongarch/mm/Makefile       |   2 +
>   arch/loongarch/mm/module_alloc.c |  10 +++
>   arch/mips/kernel/module.c        |  10 ---
>   arch/mips/mm/Makefile            |   2 +
>   arch/mips/mm/module_alloc.c      |  13 ++++
>   arch/nios2/kernel/module.c       |  20 -----
>   arch/nios2/mm/Makefile           |   2 +
>   arch/nios2/mm/module_alloc.c     |  22 ++++++
>   arch/parisc/kernel/module.c      |  12 ---
>   arch/parisc/mm/Makefile          |   1 +
>   arch/parisc/mm/module_alloc.c    |  15 ++++
>   arch/powerpc/kernel/module.c     |  36 ---------
>   arch/powerpc/mm/Makefile         |   1 +
>   arch/powerpc/mm/module_alloc.c   |  41 ++++++++++

Missing several powerpc changes to make it work. You must audit every 
use of CONFIG_MODULES inside powerpc. Here are a few exemples:

Function get_patch_pfn() to enable text code patching.

arch/powerpc/Kconfig : 	select KASAN_VMALLOC			if KASAN && MODULES

arch/powerpc/include/asm/kasan.h:

#if defined(CONFIG_MODULES) && defined(CONFIG_PPC32)
#define KASAN_KERN_START	ALIGN_DOWN(PAGE_OFFSET - SZ_256M, SZ_256M)
#else
#define KASAN_KERN_START	PAGE_OFFSET
#endif

arch/powerpc/kernel/head_8xx.S and arch/powerpc/kernel/head_book3s_32.S: 
InstructionTLBMiss interrupt handler must know that there is executable 
kernel text outside kernel core.

Function is_module_segment() to identified segments used for module text 
and set NX (NoExec) MMU flag on non-module segments.



>   arch/riscv/kernel/module.c       |  11 ---
>   arch/riscv/mm/Makefile           |   1 +
>   arch/riscv/mm/module_alloc.c     |  17 ++++
>   arch/s390/kernel/module.c        |  37 ---------
>   arch/s390/mm/Makefile            |   1 +
>   arch/s390/mm/module_alloc.c      |  42 ++++++++++
>   arch/sparc/kernel/module.c       |  31 --------
>   arch/sparc/mm/Makefile           |   2 +
>   arch/sparc/mm/module_alloc.c     |  31 ++++++++
>   arch/x86/kernel/ftrace.c         |   2 +-
>   arch/x86/kernel/module.c         |  56 -------------
>   arch/x86/mm/Makefile             |   2 +
>   arch/x86/mm/module_alloc.c       |  59 ++++++++++++++
>   fs/proc/kcore.c                  |   2 +-
>   kernel/module/Kconfig            |   1 +
>   kernel/module/main.c             |  17 ----
>   mm/Kconfig                       |   3 +
>   mm/Makefile                      |   1 +
>   mm/module_alloc.c                |  21 +++++
>   mm/vmalloc.c                     |   2 +-
>   42 files changed, 467 insertions(+), 402 deletions(-)

...

> diff --git a/mm/Kconfig b/mm/Kconfig
> index ffc3a2ba3a8c..92bfb5ae2e95 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -1261,6 +1261,9 @@ config LOCK_MM_AND_FIND_VMA
>   config IOMMU_MM_DATA
>          bool
> 
> +config MODULE_ALLOC
> +       def_bool n
> +

I'd call it something else than CONFIG_MODULE_ALLOC as you want to use 
it when CONFIG_MODULE is not selected.

Something like CONFIG_EXECMEM_ALLOC or CONFIG_DYNAMIC_EXECMEM ?



Christophe