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

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Message-ID: <6407cdf6-5dc7-96c0-343b-d2c0e1d7aaa4@amd.com>
Date:   Tue, 26 Jan 2021 14:19:53 -0600
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Peter Gonda <pgonda@...gle.com>, kvm@...r.kernel.org
Cc:     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>,
        Sean Christopherson <seanjc@...gle.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 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?

> 
> Tested: Booted SEV enabled VM on host.
> 
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: "H. Peter Anvin" <hpa@...or.com>
> Cc: Paolo Bonzini <pbonzini@...hat.com>
> Cc: Joerg Roedel <joro@...tes.org>
> Cc: Tom Lendacky <thomas.lendacky@....com>
> Cc: Brijesh Singh <brijesh.singh@....com>
> Cc: Sean Christopherson <seanjc@...gle.com>
> Cc: x86@...nel.org
> Cc: kvm@...r.kernel.org
> Cc: stable@...r.kernel.org
> Cc: linux-kernel@...r.kernel.org
> Fixes: 116a2214c5173 (KVM: SVM: Pin guest memory when SEV is active)

I can't find this commit. The Linux and KVM trees have it as:

1e80fdc09d12 ("KVM: SVM: Pin guest memory when SEV is active")

> Signed-off-by: Peter Gonda <pgonda@...gle.com>
> 
> ---
>  arch/x86/kvm/svm.c | 16 +++++++++-------

This patch won't apply, as it has already been a few releases since svm.c
was moved to the arch/x86/kvm/svm directory and this function now lives in
sev.c.

Thanks,
Tom

>  1 file changed, 9 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index afdc5b44fe9f..9884e57f3d0f 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -1699,6 +1699,8 @@ static struct page **sev_pin_memory(struct kvm *kvm, unsigned long uaddr,
>  	struct page **pages;
>  	unsigned long first, last;
>  
> +	lockdep_assert_held(&kvm->lock);
> +
>  	if (ulen == 0 || uaddr + ulen < uaddr)
>  		return NULL;
>  
> @@ -7228,12 +7230,19 @@ static int svm_register_enc_region(struct kvm *kvm,
>  	if (!region)
>  		return -ENOMEM;
>  
> +	mutex_lock(&kvm->lock);
>  	region->pages = sev_pin_memory(kvm, range->addr, range->size, &region->npages, 1);
>  	if (!region->pages) {
>  		ret = -ENOMEM;
>  		goto e_free;
>  	}
>  
> +	region->uaddr = range->addr;
> +	region->size = range->size;
> +
> +	list_add_tail(&region->list, &sev->regions_list);
> +	mutex_unlock(&kvm->lock);
> +
>  	/*
>  	 * The guest may change the memory encryption attribute from C=0 -> C=1
>  	 * or vice versa for this memory range. Lets make sure caches are
> @@ -7242,13 +7251,6 @@ static int svm_register_enc_region(struct kvm *kvm,
>  	 */
>  	sev_clflush_pages(region->pages, region->npages);
>  
> -	region->uaddr = range->addr;
> -	region->size = range->size;
> -
> -	mutex_lock(&kvm->lock);
> -	list_add_tail(&region->list, &sev->regions_list);
> -	mutex_unlock(&kvm->lock);
> -
>  	return ret;
>  
>  e_free:
>