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([2001:b07:6468:f312:c8dd:75d4:99ab:290a]) by smtp.gmail.com with ESMTPSA id v4sm31428402wrw.42.2021.01.18.09.34.19 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 18 Jan 2021 09:34:20 -0800 (PST) Subject: Re: [PATCH] KVM: x86: Add more protection against undefined behavior in rsvd_bits() To: Sean Christopherson Cc: Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , kvm@vger.kernel.org, linux-kernel@vger.kernel.org References: <20210113204515.3473079-1-seanjc@google.com> From: Paolo Bonzini Message-ID: <947f0e1a-c8db-5c68-1e0c-abadd10d92fc@redhat.com> Date: Mon, 18 Jan 2021 18:34:19 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 MIME-Version: 1.0 In-Reply-To: <20210113204515.3473079-1-seanjc@google.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 13/01/21 21:45, Sean Christopherson wrote: > Add compile-time asserts in rsvd_bits() to guard against KVM passing in > garbage hardcoded values, and cap the upper bound at '63' for dynamic > values to prevent generating a mask that would overflow a u64. > > Suggested-by: Paolo Bonzini > Signed-off-by: Sean Christopherson > --- > arch/x86/kvm/mmu.h | 9 ++++++++- > 1 file changed, 8 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h > index 581925e476d6..261be1d2032b 100644 > --- a/arch/x86/kvm/mmu.h > +++ b/arch/x86/kvm/mmu.h > @@ -44,8 +44,15 @@ > #define PT32_ROOT_LEVEL 2 > #define PT32E_ROOT_LEVEL 3 > > -static inline u64 rsvd_bits(int s, int e) > +static __always_inline u64 rsvd_bits(int s, int e) > { > + BUILD_BUG_ON(__builtin_constant_p(e) && __builtin_constant_p(s) && e < s); > + > + if (__builtin_constant_p(e)) > + BUILD_BUG_ON(e > 63); > + else > + e &= 63; > + > if (e < s) > return 0; > > Queued for 5.11, thanks. Paolo