1. 27 Apr, 2022 2 commits
    • Alexandru Elisei's avatar
      KVM/arm64: Don't emulate a PMU for 32-bit guests if feature not set · 8f6379e2
      Alexandru Elisei authored
      kvm->arch.arm_pmu is set when userspace attempts to set the first PMU
      attribute. As certain attributes are mandatory, arm_pmu ends up always
      being set to a valid arm_pmu, otherwise KVM will refuse to run the VCPU.
      However, this only happens if the VCPU has the PMU feature. If the VCPU
      doesn't have the feature bit set, kvm->arch.arm_pmu will be left
      uninitialized and equal to NULL.
      
      KVM doesn't do ID register emulation for 32-bit guests and accesses to the
      PMU registers aren't gated by the pmu_visibility() function. This is done
      to prevent injecting unexpected undefined exceptions in guests which have
      detected the presence of a hardware PMU. But even though the VCPU feature
      is missing, KVM still attempts to emulate certain aspects of the PMU when
      PMU registers are accessed. This leads to a NULL pointer dereference like
      this one, which happens on an odroid-c4 board when running the
      kvm-unit-tests pmu-cycle-counter test with kvmtool and without the PMU
      feature being set:
      
      [  454.402699] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000150
      [  454.405865] Mem abort info:
      [  454.408596]   ESR = 0x96000004
      [  454.411638]   EC = 0x25: DABT (current EL), IL = 32 bits
      [  454.416901]   SET = 0, FnV = 0
      [  454.419909]   EA = 0, S1PTW = 0
      [  454.423010]   FSC = 0x04: level 0 translation fault
      [  454.427841] Data abort info:
      [  454.430687]   ISV = 0, ISS = 0x00000004
      [  454.434484]   CM = 0, WnR = 0
      [  454.437404] user pgtable: 4k pages, 48-bit VAs, pgdp=000000000c924000
      [  454.443800] [0000000000000150] pgd=0000000000000000, p4d=0000000000000000
      [  454.450528] Internal error: Oops: 96000004 [#1] PREEMPT SMP
      [  454.456036] Modules linked in:
      [  454.459053] CPU: 1 PID: 267 Comm: kvm-vcpu-0 Not tainted 5.18.0-rc4 #113
      [  454.465697] Hardware name: Hardkernel ODROID-C4 (DT)
      [  454.470612] pstate: 60400009 (nZCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
      [  454.477512] pc : kvm_pmu_event_mask.isra.0+0x14/0x74
      [  454.482427] lr : kvm_pmu_set_counter_event_type+0x2c/0x80
      [  454.487775] sp : ffff80000a9839c0
      [  454.491050] x29: ffff80000a9839c0 x28: ffff000000a83a00 x27: 0000000000000000
      [  454.498127] x26: 0000000000000000 x25: 0000000000000000 x24: ffff00000a510000
      [  454.505198] x23: ffff000000a83a00 x22: ffff000003b01000 x21: 0000000000000000
      [  454.512271] x20: 000000000000001f x19: 00000000000003ff x18: 0000000000000000
      [  454.519343] x17: 000000008003fe98 x16: 0000000000000000 x15: 0000000000000000
      [  454.526416] x14: 0000000000000000 x13: 0000000000000000 x12: 0000000000000000
      [  454.533489] x11: 000000008003fdbc x10: 0000000000009d20 x9 : 000000000000001b
      [  454.540561] x8 : 0000000000000000 x7 : 0000000000000d00 x6 : 0000000000009d00
      [  454.547633] x5 : 0000000000000037 x4 : 0000000000009d00 x3 : 0d09000000000000
      [  454.554705] x2 : 000000000000001f x1 : 0000000000000000 x0 : 0000000000000000
      [  454.561779] Call trace:
      [  454.564191]  kvm_pmu_event_mask.isra.0+0x14/0x74
      [  454.568764]  kvm_pmu_set_counter_event_type+0x2c/0x80
      [  454.573766]  access_pmu_evtyper+0x128/0x170
      [  454.577905]  perform_access+0x34/0x80
      [  454.581527]  kvm_handle_cp_32+0x13c/0x160
      [  454.585495]  kvm_handle_cp15_32+0x1c/0x30
      [  454.589462]  handle_exit+0x70/0x180
      [  454.592912]  kvm_arch_vcpu_ioctl_run+0x1c4/0x5e0
      [  454.597485]  kvm_vcpu_ioctl+0x23c/0x940
      [  454.601280]  __arm64_sys_ioctl+0xa8/0xf0
      [  454.605160]  invoke_syscall+0x48/0x114
      [  454.608869]  el0_svc_common.constprop.0+0xd4/0xfc
      [  454.613527]  do_el0_svc+0x28/0x90
      [  454.616803]  el0_svc+0x34/0xb0
      [  454.619822]  el0t_64_sync_handler+0xa4/0x130
      [  454.624049]  el0t_64_sync+0x18c/0x190
      [  454.627675] Code: a9be7bfd 910003fd f9000bf3 52807ff3 (b9415001)
      [  454.633714] ---[ end trace 0000000000000000 ]---
      
      In this particular case, Linux hasn't detected the presence of a hardware
      PMU because the PMU node is missing from the DTB, so userspace would have
      been unable to set the VCPU PMU feature even if it attempted it. What
      happens is that the 32-bit guest reads ID_DFR0, which advertises the
      presence of the PMU, and when it tries to program a counter, it triggers
      the NULL pointer dereference because kvm->arch.arm_pmu is NULL.
      
      kvm-arch.arm_pmu was introduced by commit 46b18782 ("KVM: arm64:
      Keep a per-VM pointer to the default PMU"). Until that commit, this
      error would be triggered instead:
      
      [   73.388140] ------------[ cut here ]------------
      [   73.388189] Unknown PMU version 0
      [   73.390420] WARNING: CPU: 1 PID: 264 at arch/arm64/kvm/pmu-emul.c:36 kvm_pmu_event_mask.isra.0+0x6c/0x74
      [   73.399821] Modules linked in:
      [   73.402835] CPU: 1 PID: 264 Comm: kvm-vcpu-0 Not tainted 5.17.0 #114
      [   73.409132] Hardware name: Hardkernel ODROID-C4 (DT)
      [   73.414048] pstate: 60400009 (nZCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
      [   73.420948] pc : kvm_pmu_event_mask.isra.0+0x6c/0x74
      [   73.425863] lr : kvm_pmu_event_mask.isra.0+0x6c/0x74
      [   73.430779] sp : ffff80000a8db9b0
      [   73.434055] x29: ffff80000a8db9b0 x28: ffff000000dbaac0 x27: 0000000000000000
      [   73.441131] x26: ffff000000dbaac0 x25: 00000000c600000d x24: 0000000000180720
      [   73.448203] x23: ffff800009ffbe10 x22: ffff00000b612000 x21: 0000000000000000
      [   73.455276] x20: 000000000000001f x19: 0000000000000000 x18: ffffffffffffffff
      [   73.462348] x17: 000000008003fe98 x16: 0000000000000000 x15: 0720072007200720
      [   73.469420] x14: 0720072007200720 x13: ffff800009d32488 x12: 00000000000004e6
      [   73.476493] x11: 00000000000001a2 x10: ffff800009d32488 x9 : ffff800009d32488
      [   73.483565] x8 : 00000000ffffefff x7 : ffff800009d8a488 x6 : ffff800009d8a488
      [   73.490638] x5 : ffff0000f461a9d8 x4 : 0000000000000000 x3 : 0000000000000001
      [   73.497710] x2 : 0000000000000000 x1 : 0000000000000000 x0 : ffff000000dbaac0
      [   73.504784] Call trace:
      [   73.507195]  kvm_pmu_event_mask.isra.0+0x6c/0x74
      [   73.511768]  kvm_pmu_set_counter_event_type+0x2c/0x80
      [   73.516770]  access_pmu_evtyper+0x128/0x16c
      [   73.520910]  perform_access+0x34/0x80
      [   73.524532]  kvm_handle_cp_32+0x13c/0x160
      [   73.528500]  kvm_handle_cp15_32+0x1c/0x30
      [   73.532467]  handle_exit+0x70/0x180
      [   73.535917]  kvm_arch_vcpu_ioctl_run+0x20c/0x6e0
      [   73.540489]  kvm_vcpu_ioctl+0x2b8/0x9e0
      [   73.544283]  __arm64_sys_ioctl+0xa8/0xf0
      [   73.548165]  invoke_syscall+0x48/0x114
      [   73.551874]  el0_svc_common.constprop.0+0xd4/0xfc
      [   73.556531]  do_el0_svc+0x28/0x90
      [   73.559808]  el0_svc+0x28/0x80
      [   73.562826]  el0t_64_sync_handler+0xa4/0x130
      [   73.567054]  el0t_64_sync+0x1a0/0x1a4
      [   73.570676] ---[ end trace 0000000000000000 ]---
      [   73.575382] kvm: pmu event creation failed -2
      
      The root cause remains the same: kvm->arch.pmuver was never set to
      something sensible because the VCPU feature itself was never set.
      
      The odroid-c4 is somewhat of a special case, because Linux doesn't probe
      the PMU. But the above errors can easily be reproduced on any hardware,
      with or without a PMU driver, as long as userspace doesn't set the PMU
      feature.
      
      Work around the fact that KVM advertises a PMU even when the VCPU feature
      is not set by gating all PMU emulation on the feature. The guest can still
      access the registers without KVM injecting an undefined exception.
      Signed-off-by: default avatarAlexandru Elisei <alexandru.elisei@arm.com>
      Signed-off-by: default avatarMarc Zyngier <maz@kernel.org>
      Link: https://lore.kernel.org/r/20220425145530.723858-1-alexandru.elisei@arm.com
      8f6379e2
    • Will Deacon's avatar
      KVM: arm64: Handle host stage-2 faults from 32-bit EL0 · 2a50fc5f
      Will Deacon authored
      When pKVM is enabled, host memory accesses are translated by an identity
      mapping at stage-2, which is populated lazily in response to synchronous
      exceptions from 64-bit EL1 and EL0.
      
      Extend this handling to cover exceptions originating from 32-bit EL0 as
      well. Although these are very unlikely to occur in practice, as the
      kernel typically ensures that user pages are initialised before mapping
      them in, drivers could still map previously untouched device pages into
      userspace and expect things to work rather than panic the system.
      
      Cc: Quentin Perret <qperret@google.com>
      Cc: Marc Zyngier <maz@kernel.org>
      Signed-off-by: default avatarWill Deacon <will@kernel.org>
      Signed-off-by: default avatarMarc Zyngier <maz@kernel.org>
      Link: https://lore.kernel.org/r/20220427171332.13635-1-will@kernel.org
      2a50fc5f
  2. 07 Apr, 2022 4 commits
  3. 06 Apr, 2022 7 commits
  4. 03 Apr, 2022 8 commits
  5. 02 Apr, 2022 19 commits