[00/19] KVM: arm64: vgic-v3 userspace access consolidation (and other goodies)

Message

Marc Zyngier July 6, 2022, 4:42 p.m. UTC

Schspa Shi recently reported[1] that some of the vgic code interacting
with userspace was reading uninitialised stack memory, and although
that read wasn't used any further, it prompted me to revisit this part
of the code.

Needless to say, this area of the kernel is pretty crufty, and shows a
bunch of issues in other parts of the KVM/arm64 infrastructure. This
series tries to remedy a bunch of them:

- Sanitise the way we deal with sysregs from userspace: at the moment,
  each and every .set_user/.get_user callback has to implement its own
  userspace accesses (directly or indirectly). It'd be much better if
  that was centralised so that we can reason about it.

- Enforce that all AArch64 sysregs are 64bit. Always. This was sort of
  implied by the code, but it took some effort to convince myself that
  this was actually the case.

- Move the vgic-v3 sysreg userspace accessors to the userspace
  callbacks instead of hijacking the vcpu trap callback. This allows
  us to reuse the sysreg infrastructure.

- Consolidate userspace accesses for both GICv2, GICv3 and common code
  as much as possible.

- Cleanup a bunch of not-very-useful helpers, tidy up some of the code
  as we touch it.

Overall, this is essentially a cosmetic exercise, as there is no new
feature here. But I have the feeling that the result is somehow more
maintainable. This has been (lightly) tested on my Synquacer, and
nothing exploded. Yet. YMMV.

[1] https://lore.kernel.org/r/[e-mail]

Marc Zyngier (19):
  KVM: arm64: Add get_reg_by_id() as a sys_reg_desc retrieving helper
  KVM: arm64: Reorder handling of invariant sysregs from userspace
  KVM: arm64: Introduce generic get_user/set_user helpers for system
    registers
  KVM: arm64: Push checks for 64bit registers into the low-level
    accessors
  KVM: arm64: Consolidate sysreg userspace accesses
  KVM: arm64: Get rid of reg_from/to_user()
  KVM: arm64: vgic-v3: Simplify vgic_v3_has_cpu_sysregs_attr()
  KVM: arm64: vgic-v3: Push user access into
    vgic_v3_cpu_sysregs_uaccess()
  KVM: arm64: vgic-v3: Make the userspace accessors use sysreg API
  KVM: arm64: vgic-v3: Convert userspace accessors over to
    FIELD_GET/FIELD_PREP
  KVM: arm64: vgic-v3: Use u32 to manage the line level from userspace
  KVM: arm64: vgic-v3: Consolidate userspace access for MMIO registers
  KVM: arm64: vgic-v2: Consolidate userspace access for MMIO registers
  KVM: arm64: vgic: Use {get,put}_user() instead of copy_{from.to}_user
  KVM: arm64: vgic-v2: Add helper for legacy dist/cpuif base address
    setting
  KVM: arm64: vgic: Consolidate userspace access for base address
    setting
  KVM: arm64: Get rid of find_reg_by_id()
  KVM: arm64: Descope kvm_arm_sys_reg_{get,set}_reg()
  KVM: arm64: Get rid or outdated comments

 arch/arm64/include/asm/kvm_host.h     |   2 -
 arch/arm64/kvm/arm.c                  |  11 +-
 arch/arm64/kvm/sys_regs.c             | 291 +++++++---------
 arch/arm64/kvm/sys_regs.h             |  18 +-
 arch/arm64/kvm/vgic-sys-reg-v3.c      | 461 +++++++++++++++-----------
 arch/arm64/kvm/vgic/vgic-kvm-device.c | 269 +++++++--------
 arch/arm64/kvm/vgic/vgic-mmio-v3.c    |  10 +-
 arch/arm64/kvm/vgic/vgic-mmio.c       |   6 +-
 arch/arm64/kvm/vgic/vgic-mmio.h       |   4 +-
 arch/arm64/kvm/vgic/vgic.h            |   9 +-
 include/kvm/arm_vgic.h                |   2 +-
 11 files changed, 535 insertions(+), 548 deletions(-)