Re: [PATCH v2 5/8] crypto: ccp: Use the stack for small SEV command buffers

From: Paolo Bonzini <pbonzini@redhat.com>
To: Sean Christopherson <seanjc@google.com>,
	Brijesh Singh <brijesh.singh@amd.com>,
	Tom Lendacky <thomas.lendacky@amd.com>,
	John Allen <john.allen@amd.com>
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
	kvm@vger.kernel.org, linux-crypto@vger.kernel.org,
	linux-kernel@vger.kernel.org, Borislav Petkov <bp@suse.de>,
	Christophe Leroy <christophe.leroy@csgroup.eu>
Subject: Re: [PATCH v2 5/8] crypto: ccp: Use the stack for small SEV command buffers
Date: Sat, 17 Apr 2021 14:40:39 +0200	[thread overview]
Message-ID: <587677cf-2db1-1bed-18fc-dbbc1c1dffed@redhat.com> (raw)
In-Reply-To: <20210406224952.4177376-6-seanjc@google.com>

On 07/04/21 00:49, Sean Christopherson wrote:
> For commands with small input/output buffers, use the local stack to
> "allocate" the structures used to communicate with the PSP.   Now that
> __sev_do_cmd_locked() gracefully handles vmalloc'd buffers, there's no
> reason to avoid using the stack, e.g. CONFIG_VMAP_STACK=y will just work.
> 
> Signed-off-by: Sean Christopherson <seanjc@google.com>

Squashing this in (inspired by Christophe's review, though not quite
matching his suggestion).

diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c
index 0f5644a3b138..246b281b6376 100644
--- a/drivers/crypto/ccp/sev-dev.c
+++ b/drivers/crypto/ccp/sev-dev.c
@@ -408,12 +408,11 @@ static int sev_ioctl_do_pek_csr(struct sev_issue_cmd *argp, bool writable)
  	if (copy_from_user(&input, (void __user *)argp->data, sizeof(input)))
  		return -EFAULT;
  
+	memset(&data, 0, sizeof(data));
+
  	/* userspace wants to query CSR length */
-	if (!input.address || !input.length) {
-		data.address = 0;
-		data.len = 0;
+	if (!input.address || !input.length)
  		goto cmd;
-	}
  
  	/* allocate a physically contiguous buffer to store the CSR blob */
  	input_address = (void __user *)input.address;


