linux-kernel - [PATCH v2 0/3] KVM: x86: Out-of-bounds access in kvm_recalculate_phys

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Message-ID: <20230526235048.2842761-1-seanjc@google.com>
Date:   Fri, 26 May 2023 16:50:45 -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,
        Michal Luczaj <mhal@...x.co>
Subject: [PATCH v2 0/3] KVM: x86: Out-of-bounds access in kvm_recalculate_phys_map()

v2 of Michal's fix for a TOCTOU bug in kvm_recalculate_phys_map().   Not
fully tested (will do that next week), though I did confirm the reworked
selftest can hit the bug.  Posting a bit prematurely as I have a long weekend
and I don't want Michal to do any duplicate work.

In Michal's words...

kvm_recalculate_apic_map() creates the APIC map iterating over the list of
vCPUs twice. First to find the max APIC ID and allocate a max-sized buffer,
then again, calling kvm_recalculate_phys_map() for each vCPU. This opens a
race window: value of max APIC ID can increase _after_ the buffer was
allocated.

Michal Luczaj (1):
  KVM: selftests: Add test for race in kvm_recalculate_apic_map()

Sean Christopherson (2):
  KVM: x86: Bail from kvm_recalculate_phys_map() if x2APIC ID is
    out-of-bounds
  KVM: x86: Retry APIC optimized map recalc if vCPU is added/enabled

 arch/x86/kvm/lapic.c                          | 49 ++++++++++--
 tools/testing/selftests/kvm/Makefile          |  1 +
 .../kvm/x86_64/recalc_apic_map_race.c         | 76 +++++++++++++++++++
 3 files changed, 120 insertions(+), 6 deletions(-)
 create mode 100644 tools/testing/selftests/kvm/x86_64/recalc_apic_map_race.c

base-commit: 39428f6ea9eace95011681628717062ff7f5eb5f
-- 
2.41.0.rc0.172.g3f132b7071-goog