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

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Date:   Sat, 17 Apr 2021 14:40:39 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Brijesh Singh <brijesh.singh@....com>,
        Tom Lendacky <thomas.lendacky@....com>,
        John Allen <john.allen@....com>
Cc:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org,
        Borislav Petkov <bp@...e.de>,
        Christophe Leroy <christophe.leroy@...roup.eu>
Subject: Re: [PATCH v2 5/8] crypto: ccp: Use the stack for small SEV command
 buffers

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@...gle.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;