linux-kernel - Re: [PATCH] Fix unsynchronized access to sev members through svm_register_enc

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Date:   Tue, 26 Jan 2021 15:10:08 -0800
From:   Sean Christopherson <seanjc@...gle.com>
To:     Tom Lendacky <thomas.lendacky@....com>
Cc:     Peter Gonda <pgonda@...gle.com>, kvm@...r.kernel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Joerg Roedel <joro@...tes.org>,
        Brijesh Singh <brijesh.singh@....com>, x86@...nel.org,
        stable@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Fix unsynchronized access to sev members through
 svm_register_enc_region

On Tue, Jan 26, 2021, Tom Lendacky wrote:
> On 1/26/21 12:54 PM, Peter Gonda wrote:
> > sev_pin_memory assumes that callers hold the kvm->lock. This was true for
> > all callers except svm_register_enc_region since it does not originate
> > from svm_mem_enc_op. Also added lockdep annotation to help prevent
> > future regressions.
> 
> I'm not exactly sure what the problem is that your fixing? What is the
> symptom that you're seeing?

svm_register_enc_region() calls sev_pin_memory() without holding kvm->lock.  If
userspace does multiple KVM_MEMORY_ENCRYPT_REG_REGION in parallel, it could
circumvent the rlimit(RLIMIT_MEMLOCK) check.