KVM: SEV: Fix uninitialized firmware error code

[PATCH] KVM: SEV: Fix uninitialized firmware error code

Posted by Michael Roth 2 years, 1 month ago

The current code triggers a clang warning due to passing back an
uninitialized firmware return code in cases where an attestation request
is aborted before getting sent to userspace. Since firmware has not been
involved at this point the appropriate value is 0.

Reported-by: Nathan Chancellor <nathan@kernel.org>
Closes: https://lore.kernel.org/kvm/20240513151920.GA3061950@thelio-3990X/
Fixes: 32fde9e18b3f ("KVM: SEV: Provide support for SNP_EXTENDED_GUEST_REQUEST NAE event")
Signed-off-by: Michael Roth <michael.roth@amd.com>
---
 arch/x86/kvm/svm/sev.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 57c2c8025547..59c0d89a4d52 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -4048,7 +4048,6 @@ static int snp_begin_ext_guest_req(struct kvm_vcpu *vcpu)
 	int vmm_ret = SNP_GUEST_VMM_ERR_GENERIC;
 	struct vcpu_svm *svm = to_svm(vcpu);
 	unsigned long data_npages;
-	sev_ret_code fw_err;
 	gpa_t data_gpa;
 
 	if (!sev_snp_guest(vcpu->kvm))
@@ -4075,7 +4074,7 @@ static int snp_begin_ext_guest_req(struct kvm_vcpu *vcpu)
 	return 0; /* forward request to userspace */
 
 abort_request:
-	ghcb_set_sw_exit_info_2(svm->sev_es.ghcb, SNP_GUEST_ERR(vmm_ret, fw_err));
+	ghcb_set_sw_exit_info_2(svm->sev_es.ghcb, SNP_GUEST_ERR(vmm_ret, 0));
 	return 1; /* resume guest */
 }
 
-- 
2.25.1

Re: [PATCH] KVM: SEV: Fix uninitialized firmware error code

Posted by Nathan Chancellor 2 years, 1 month ago

On Mon, May 13, 2024 at 12:27:04PM -0500, Michael Roth wrote:
> The current code triggers a clang warning due to passing back an
> uninitialized firmware return code in cases where an attestation request
> is aborted before getting sent to userspace. Since firmware has not been
> involved at this point the appropriate value is 0.
> 
> Reported-by: Nathan Chancellor <nathan@kernel.org>
> Closes: https://lore.kernel.org/kvm/20240513151920.GA3061950@thelio-3990X/
> Fixes: 32fde9e18b3f ("KVM: SEV: Provide support for SNP_EXTENDED_GUEST_REQUEST NAE event")
> Signed-off-by: Michael Roth <michael.roth@amd.com>

This obviously resolves the warning:

Tested-by: Nathan Chancellor <nathan@kernel.org> # build

> ---
>  arch/x86/kvm/svm/sev.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index 57c2c8025547..59c0d89a4d52 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -4048,7 +4048,6 @@ static int snp_begin_ext_guest_req(struct kvm_vcpu *vcpu)
>  	int vmm_ret = SNP_GUEST_VMM_ERR_GENERIC;
>  	struct vcpu_svm *svm = to_svm(vcpu);
>  	unsigned long data_npages;
> -	sev_ret_code fw_err;
>  	gpa_t data_gpa;
>  
>  	if (!sev_snp_guest(vcpu->kvm))
> @@ -4075,7 +4074,7 @@ static int snp_begin_ext_guest_req(struct kvm_vcpu *vcpu)
>  	return 0; /* forward request to userspace */
>  
>  abort_request:
> -	ghcb_set_sw_exit_info_2(svm->sev_es.ghcb, SNP_GUEST_ERR(vmm_ret, fw_err));
> +	ghcb_set_sw_exit_info_2(svm->sev_es.ghcb, SNP_GUEST_ERR(vmm_ret, 0));
>  	return 1; /* resume guest */
>  }
>  
> -- 
> 2.25.1
>