linux-kernel - [PATCH v4 0/6] KVM: x86: Fix unpermitted XTILE CPUID reporting

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Message-ID: <20230405004520.421768-1-seanjc@google.com>
Date:   Tue,  4 Apr 2023 17:45:14 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Aaron Lewis <aaronlewis@...gle.com>,
        Mingwei Zhang <mizhang@...gle.com>,
        Jim Mattson <jmattson@...gle.com>
Subject: [PATCH v4 0/6] KVM: x86: Fix unpermitted XTILE CPUID reporting

This is v4 of Aaron's "Clean up the supported xfeatures" series.

Fix a bug where KVM treats/reports XTILE_CFG as supported without
XTILE_DATA being supported if userspace queries the supported CPUID but
doesn't request access to AMX, a.k.a. XTILE_DATA.  If userspace reflects
that CPUID info back into KVM, the resulting VM may use it verbatim and
attempt to shove bad data into XCR0: XTILE_CFG and XTILE_DATA must be
set/cleared as a pair in XCR0, despite being enumerated separately.

This is effectively compile-tested only on my end.

v4:
 - Apply the massaging _only to the XTILE case.
 - Add a build-time assertion to trigger a failure if a new dynamic
   XFeature comes along without updating kvm_get_filtered_xcr0().

v3: https://lore.kernel.org/all/20230224223607.1580880-1-aaronlewis@google.com

Aaron Lewis (4):
  KVM: x86: Add a helper to handle filtering of unpermitted XCR0
    features
  KVM: selftests: Move XGETBV and XSETBV helpers to common code
  KVM: selftests: Add all known XFEATURE masks to common code
  KVM: selftests: Add test to verify KVM's supported XCR0

Sean Christopherson (2):
  KVM: x86: Filter out XTILE_CFG if XTILE_DATA isn't permitted
  KVM: selftests: Rework dynamic XFeature helper to take mask, not bit

 arch/x86/kvm/cpuid.c                          |   2 +-
 arch/x86/kvm/x86.c                            |   4 +-
 arch/x86/kvm/x86.h                            |  29 ++++
 tools/testing/selftests/kvm/Makefile          |   1 +
 .../selftests/kvm/include/x86_64/processor.h  |  69 +++++++--
 .../selftests/kvm/lib/x86_64/processor.c      |  17 ++-
 tools/testing/selftests/kvm/x86_64/amx_test.c |  62 +++-----
 .../selftests/kvm/x86_64/xcr0_cpuid_test.c    | 132 ++++++++++++++++++
 8 files changed, 251 insertions(+), 65 deletions(-)
 create mode 100644 tools/testing/selftests/kvm/x86_64/xcr0_cpuid_test.c


base-commit: 27d6845d258b67f4eb3debe062b7dacc67e0c393
-- 
2.40.0.348.gf938b09366-goog