Re: [PATCH] KVM: x86/pmu: Fix UBSAN shift-out-of-bounds warning in intel_pmu_refresh()

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Ping ?

On 2020/12/29 15:11, Like Xu wrote:
Since we know vPMU will not work properly when the guest bit_width(s) of
the [gp|fixed] counters are greater than the host ones, so we can setup a
smaller left shift value and refresh the guest pmu cpuid entry, thus fixing
the following UBSAN shift-out-of-bounds warning:

shift exponent 197 is too large for 64-bit type 'long long unsigned int'

Call Trace:
  __dump_stack lib/dump_stack.c:79 [inline]
  dump_stack+0x107/0x163 lib/dump_stack.c:120
  ubsan_epilogue+0xb/0x5a lib/ubsan.c:148
  __ubsan_handle_shift_out_of_bounds.cold+0xb1/0x181 lib/ubsan.c:395
  intel_pmu_refresh.cold+0x75/0x99 arch/x86/kvm/vmx/pmu_intel.c:348
  kvm_vcpu_after_set_cpuid+0x65a/0xf80 arch/x86/kvm/cpuid.c:177
  kvm_vcpu_ioctl_set_cpuid2+0x160/0x440 arch/x86/kvm/cpuid.c:308
  kvm_arch_vcpu_ioctl+0x11b6/0x2d70 arch/x86/kvm/x86.c:4709
  kvm_vcpu_ioctl+0x7b9/0xdb0 arch/x86/kvm/../../../virt/kvm/kvm_main.c:3386
  vfs_ioctl fs/ioctl.c:48 [inline]
  __do_sys_ioctl fs/ioctl.c:753 [inline]
  __se_sys_ioctl fs/ioctl.c:739 [inline]
  __x64_sys_ioctl+0x193/0x200 fs/ioctl.c:739
  do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
  entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported-by: syzbot+ae488dc136a4cc6ba32b@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Like Xu <like.xu@xxxxxxxxxxxxxxx>
---
  arch/x86/kvm/vmx/pmu_intel.c | 3 +++
  1 file changed, 3 insertions(+)

diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c
index a886a47daebd..a86a1690e75c 100644
--- a/arch/x86/kvm/vmx/pmu_intel.c
+++ b/arch/x86/kvm/vmx/pmu_intel.c
@@ -345,6 +345,7 @@ static void intel_pmu_refresh(struct kvm_vcpu *vcpu)
pmu->nr_arch_gp_counters = min_t(int, eax.split.num_counters,
  					 x86_pmu.num_counters_gp);
+	eax.split.bit_width = min_t(int, eax.split.bit_width, x86_pmu.bit_width_gp);
  	pmu->counter_bitmask[KVM_PMC_GP] = ((u64)1 << eax.split.bit_width) - 1;
  	pmu->available_event_types = ~entry->ebx &
  					((1ull << eax.split.mask_length) - 1);
@@ -355,6 +356,8 @@ static void intel_pmu_refresh(struct kvm_vcpu *vcpu)
  		pmu->nr_arch_fixed_counters =
  			min_t(int, edx.split.num_counters_fixed,
  			      x86_pmu.num_counters_fixed);
+		edx.split.bit_width_fixed = min_t(int,
+			edx.split.bit_width_fixed, x86_pmu.bit_width_fixed);
  		pmu->counter_bitmask[KVM_PMC_FIXED] =
  			((u64)1 << edx.split.bit_width_fixed) - 1;
  	}




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