linux-kernel - Re: [PATCH v2] KVM: x86/pmu: Fix UBSAN shift-out-of-bounds warning in intel_pmu

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Message-ID: <53930fc4-46d8-ce87-daa9-00460c6adb63@redhat.com>
Date:   Mon, 18 Jan 2021 18:56:15 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Like Xu <like.xu@...ux.intel.com>,
        Sean Christopherson <seanjc@...gle.com>
Cc:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] KVM: x86/pmu: Fix UBSAN shift-out-of-bounds warning in
 intel_pmu_refresh()

On 18/01/21 03:58, Like Xu wrote:
> Since we know vPMU will not work properly when (1) the guest bit_width(s)
> of the [gp|fixed] counters are greater than the host ones, or (2) guest
> requested architectural events exceeds the range supported by the host, so
> we can setup a smaller left shift value and refresh the guest 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@...kaller.appspotmail.com
> Signed-off-by: Like Xu <like.xu@...ux.intel.com>
> ---
> v1->v2 Changelog:
> - Add similar treatment for eax.split.mask_length (Sean)
> 
>   arch/x86/kvm/vmx/pmu_intel.c | 4 ++++
>   1 file changed, 4 insertions(+)
> 
> diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c
> index a886a47daebd..d1584ae6625a 100644
> --- a/arch/x86/kvm/vmx/pmu_intel.c
> +++ b/arch/x86/kvm/vmx/pmu_intel.c
> @@ -345,7 +345,9 @@ 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;
> +	eax.split.mask_length = min_t(int, eax.split.mask_length, x86_pmu.events_mask_len);
>   	pmu->available_event_types = ~entry->ebx &
>   					((1ull << eax.split.mask_length) - 1);
>   
> @@ -355,6 +357,8 @@ 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;
>   	}
> 

Queued, thanks.

Paolo