linux-kernel - Re: [PATCH] KVM: x86: Free kvm_cpuid_entry2 array on post-KVM_RUN KVM_SET

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Message-ID: <875yq6iwjc.fsf@redhat.com>
Date:   Wed, 26 Jan 2022 12:08:55 +0100
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        syzbot+be576ad7655690586eec@...kaller.appspotmail.com
Subject: Re: [PATCH] KVM: x86: Free kvm_cpuid_entry2 array on post-KVM_RUN
 KVM_SET_CPUID{,2}

Sean Christopherson <seanjc@...gle.com> writes:

> Free the "struct kvm_cpuid_entry2" array on successful post-KVM_RUN
> KVM_SET_CPUID{,2} to fix a memory leak, the callers of kvm_set_cpuid()
> free the array only on failure.
>
>  BUG: memory leak
>  unreferenced object 0xffff88810963a800 (size 2048):
>   comm "syz-executor025", pid 3610, jiffies 4294944928 (age 8.080s)
>   hex dump (first 32 bytes):
>     00 00 00 00 00 00 00 00 00 00 00 00 0d 00 00 00  ................
>     47 65 6e 75 6e 74 65 6c 69 6e 65 49 00 00 00 00  GenuntelineI....
>   backtrace:
>     [<ffffffff814948ee>] kmalloc_node include/linux/slab.h:604 [inline]
>     [<ffffffff814948ee>] kvmalloc_node+0x3e/0x100 mm/util.c:580
>     [<ffffffff814950f2>] kvmalloc include/linux/slab.h:732 [inline]
>     [<ffffffff814950f2>] vmemdup_user+0x22/0x100 mm/util.c:199
>     [<ffffffff8109f5ff>] kvm_vcpu_ioctl_set_cpuid2+0x8f/0xf0 arch/x86/kvm/cpuid.c:423
>     [<ffffffff810711b9>] kvm_arch_vcpu_ioctl+0xb99/0x1e60 arch/x86/kvm/x86.c:5251
>     [<ffffffff8103e92d>] kvm_vcpu_ioctl+0x4ad/0x950 arch/x86/kvm/../../../virt/kvm/kvm_main.c:4066
>     [<ffffffff815afacc>] vfs_ioctl fs/ioctl.c:51 [inline]
>     [<ffffffff815afacc>] __do_sys_ioctl fs/ioctl.c:874 [inline]
>     [<ffffffff815afacc>] __se_sys_ioctl fs/ioctl.c:860 [inline]
>     [<ffffffff815afacc>] __x64_sys_ioctl+0xfc/0x140 fs/ioctl.c:860
>     [<ffffffff844a3335>] do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>     [<ffffffff844a3335>] do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
>     [<ffffffff84600068>] entry_SYSCALL_64_after_hwframe+0x44/0xae
>
> Fixes: c6617c61e8fe ("KVM: x86: Partially allow KVM_SET_CPUID{,2} after KVM_RUN")
> Cc: stable@...r.kernel.org
> Reported-by: syzbot+be576ad7655690586eec@...kaller.appspotmail.com
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>  arch/x86/kvm/cpuid.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index 3902c28fb6cb..0a08db384fb9 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -346,8 +346,14 @@ static int kvm_set_cpuid(struct kvm_vcpu *vcpu, struct kvm_cpuid_entry2 *e2,
>  	 * KVM_SET_CPUID{,2} again. To support this legacy behavior, check
>  	 * whether the supplied CPUID data is equal to what's already set.
>  	 */
> -	if (vcpu->arch.last_vmentry_cpu != -1)
> -		return kvm_cpuid_check_equal(vcpu, e2, nent);
> +	if (vcpu->arch.last_vmentry_cpu != -1) {
> +		r = kvm_cpuid_check_equal(vcpu, e2, nent);
> +		if (r)
> +			return r;
> +
> +		kvfree(e2);
> +		return 0;
> +	}
>  
>  	r = kvm_check_cpuid(vcpu, e2, nent);
>  	if (r)
>
> base-commit: e2e83a73d7ce66f62c7830a85619542ef59c90e4

Reviewed-by: Vitaly Kuznetsov <vkuznets@...hat.com>

Thanks!

-- 
Vitaly