Re: [PATCH 0/4] x86: Further harden function pointers

[Jan Beulich <jbeulich@xxxxxxxx>]

On 26.11.2021 22:22, Andrew Cooper wrote:
> Slightly RFC, because patch 2 has some minor structure (ab)use, but the result
> works alarmingly well.  So far, this demonstrates converting two subsystems.
> 
> hvm_funcs is the other area of especially low hanging fruit, but IOMMU, vPMU
> also look like good candidates.  Anything which is partially altcall'd already
> would benefit from being fully altcall'd.

I'll post patches for hvm_funcs and vPMU hopefully later today. I intend
to look into the remaining unconverted IOMMU instances (so far I've
spotted one, but proper auditing may turn up more). For hvm_funcs what I
have leaves a few ones still unconverted; I guess we can discuss whether
to go beyond what I have in the context of that patch.

> Should we consider introducing __ro_after_init right now (as an alias to
> __read_mostly) as this conversion is touching a lot of ares where true
> post-init immutability ought to be enforced.

Well, it's largely orthogonal, but this might indeed be a good opportunity
to at least make a first step. I'd go slightly beyond what you say and at
least also introduce a respective new section, rather than aliasing
__read_mostly.

Jan

> Andrew Cooper (4):
>   x86/altcall: Check and optimise altcall targets
>   x86/altcall: Optimise away endbr64 instruction where possible
>   xen/xsm: Use __init_data_cf_clobber for xsm_ops
>   x86/ucode: Use altcall, and __initdata_cf_clobber
> 
>  xen/arch/x86/alternative.c           | 60 
> ++++++++++++++++++++++++++++++++++++
>  xen/arch/x86/cpu/microcode/amd.c     |  2 +-
>  xen/arch/x86/cpu/microcode/core.c    | 38 ++++++++++++-----------
>  xen/arch/x86/cpu/microcode/intel.c   |  2 +-
>  xen/arch/x86/cpu/microcode/private.h |  2 +-
>  xen/arch/x86/xen.lds.S               |  5 +++
>  xen/include/xen/init.h               |  2 ++
>  xen/xsm/dummy.c                      |  2 +-
>  xen/xsm/flask/hooks.c                |  2 +-
>  xen/xsm/silo.c                       |  2 +-
>  10 files changed, 93 insertions(+), 24 deletions(-)
>