linux-kernel - Re: [PATCH v6 2/8] KVM: SVM: Fix snp_context

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Message-ID: <4d5be1b5-1a05-00a8-bd00-96ee914c38b4@amd.com>
Date: Wed, 13 Nov 2024 09:39:52 -0600
From: Tom Lendacky <thomas.lendacky@....com>
To: Dionna Glaze <dionnaglaze@...gle.com>, linux-kernel@...r.kernel.org,
 x86@...nel.org, Sean Christopherson <seanjc@...gle.com>,
 Paolo Bonzini <pbonzini@...hat.com>, Thomas Gleixner <tglx@...utronix.de>,
 Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
 Dave Hansen <dave.hansen@...ux.intel.com>, "H. Peter Anvin" <hpa@...or.com>,
 Brijesh Singh <brijesh.singh@....com>, Michael Roth <michael.roth@....com>,
 Ashish Kalra <ashish.kalra@....com>
Cc: linux-coco@...ts.linux.dev, John Allen <john.allen@....com>,
 Herbert Xu <herbert@...dor.apana.org.au>,
 "David S. Miller" <davem@...emloft.net>, Luis Chamberlain
 <mcgrof@...nel.org>, Russ Weight <russ.weight@...ux.dev>,
 Danilo Krummrich <dakr@...hat.com>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 "Rafael J. Wysocki" <rafael@...nel.org>,
 Tianfei zhang <tianfei.zhang@...el.com>, Alexey Kardashevskiy <aik@....com>,
 stable@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH v6 2/8] KVM: SVM: Fix snp_context_create error reporting

On 11/12/24 17:22, Dionna Glaze wrote:
> Failure to allocate should not return -ENOTTY.
> Command failure has multiple possible error modes.
> 
> Fixes: 136d8bc931c8 ("KVM: SEV: Add KVM_SEV_SNP_LAUNCH_START command")
> 
> CC: Sean Christopherson <seanjc@...gle.com>
> CC: Paolo Bonzini <pbonzini@...hat.com>
> CC: Thomas Gleixner <tglx@...utronix.de>
> CC: Ingo Molnar <mingo@...hat.com>
> CC: Borislav Petkov <bp@...en8.de>
> CC: Dave Hansen <dave.hansen@...ux.intel.com>
> CC: Ashish Kalra <ashish.kalra@....com>
> CC: Tom Lendacky <thomas.lendacky@....com>
> CC: John Allen <john.allen@....com>
> CC: Herbert Xu <herbert@...dor.apana.org.au>
> CC: "David S. Miller" <davem@...emloft.net>
> CC: Michael Roth <michael.roth@....com>
> CC: Luis Chamberlain <mcgrof@...nel.org>
> CC: Russ Weight <russ.weight@...ux.dev>
> CC: Danilo Krummrich <dakr@...hat.com>
> CC: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> CC: "Rafael J. Wysocki" <rafael@...nel.org>
> CC: Tianfei zhang <tianfei.zhang@...el.com>
> CC: Alexey Kardashevskiy <aik@....com>
> CC: stable@...r.kernel.org
> 
> Signed-off-by: Dionna Glaze <dionnaglaze@...gle.com>
> ---
>  arch/x86/kvm/svm/sev.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index 357906375ec59..d0e0152aefb32 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -2171,7 +2171,7 @@ static void *snp_context_create(struct kvm *kvm, struct kvm_sev_cmd *argp)
>  	/* Allocate memory for context page */
>  	context = snp_alloc_firmware_page(GFP_KERNEL_ACCOUNT);
>  	if (!context)
> -		return NULL;
> +		return ERR_PTR(-ENOMEM);
>  
>  	data.address = __psp_pa(context);
>  	rc = __sev_issue_cmd(argp->sev_fd, SEV_CMD_SNP_GCTX_CREATE, &data, &argp->error);
> @@ -2179,7 +2179,7 @@ static void *snp_context_create(struct kvm *kvm, struct kvm_sev_cmd *argp)
>  		pr_warn("Failed to create SEV-SNP context, rc %d fw_error %d",
>  			rc, argp->error);
>  		snp_free_firmware_page(context);
> -		return NULL;
> +		return ERR_PTR(rc);
>  	}
>  
>  	return context;
> @@ -2227,8 +2227,8 @@ static int snp_launch_start(struct kvm *kvm, struct kvm_sev_cmd *argp)
>  		return -EINVAL;
>  
>  	sev->snp_context = snp_context_create(kvm, argp);

Since you can now get an error value set into sev->snp_context, a lot of
the NULL checks will be altered. You should create a local variable to
hold the returned value of snp_context_create() and only set
sev->snp_context if not an error.

Thanks,
Tom

> -	if (!sev->snp_context)
> -		return -ENOTTY;
> +	if (IS_ERR(sev->snp_context))
> +		return PTR_ERR(sev->snp_context);
>  
>  	start.gctx_paddr = __psp_pa(sev->snp_context);
>  	start.policy = params.policy;