linux-kernel - [PATCH] KVM: SVM: Mark SEV launch secret pages as dirty.

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Message-Id: <20200925020011.1159247-1-cfir@google.com>
Date:   Thu, 24 Sep 2020 19:00:11 -0700
From:   Cfir Cohen <cfir@...gle.com>
To:     "kvm @ vger . kernel . org" <kvm@...r.kernel.org>,
        Lendacky Thomas <thomas.lendacky@....com>,
        Singh Brijesh <brijesh.singh@....com>
Cc:     Grimm Jon <Jon.Grimm@....com>,
        David Rientjes <rientjes@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Cfir Cohen <cfir@...gle.com>
Subject: [PATCH] KVM: SVM: Mark SEV launch secret pages as dirty.

The LAUNCH_SECRET command performs encryption of the
launch secret memory contents. Mark pinned pages as
dirty, before unpinning them.
This matches the logic in sev_launch_update_data().

Fixes: 9c5e0afaf157 ("KVM: SVM: Add support for SEV LAUNCH_SECRET command")
Signed-off-by: Cfir Cohen <cfir@...gle.com>
---
Changelog since v2:
 - Added 'Fixes' tag, updated comments.
Changelog since v1:
 - Updated commit message.

 arch/x86/kvm/svm/sev.c | 26 +++++++++++++++++---------
 1 file changed, 17 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 5573a97f1520..55edaf3577a0 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -440,10 +440,8 @@ static int sev_launch_update_data(struct kvm *kvm, struct kvm_sev_cmd *argp)
 	}
 
 	/*
-	 * The LAUNCH_UPDATE command will perform in-place encryption of the
-	 * memory content (i.e it will write the same memory region with C=1).
-	 * It's possible that the cache may contain the data with C=0, i.e.,
-	 * unencrypted so invalidate it first.
+	 * Flush (on non-coherent CPUs) before LAUNCH_UPDATE encrypts pages in
+	 * place, the cache may contain data that was written unencrypted.
 	 */
 	sev_clflush_pages(inpages, npages);
 
@@ -799,10 +797,9 @@ static int sev_dbg_crypt(struct kvm *kvm, struct kvm_sev_cmd *argp, bool dec)
 		}
 
 		/*
-		 * The DBG_{DE,EN}CRYPT commands will perform {dec,en}cryption of the
-		 * memory content (i.e it will write the same memory region with C=1).
-		 * It's possible that the cache may contain the data with C=0, i.e.,
-		 * unencrypted so invalidate it first.
+		 * Flush (on non-coherent CPUs) before DBG_{DE,EN}CRYPT reads or modifies
+		 * the pages, flush the destination too in case the cache contains its
+		 * current data.
 		 */
 		sev_clflush_pages(src_p, 1);
 		sev_clflush_pages(dst_p, 1);
@@ -850,7 +847,7 @@ static int sev_launch_secret(struct kvm *kvm, struct kvm_sev_cmd *argp)
 	struct kvm_sev_launch_secret params;
 	struct page **pages;
 	void *blob, *hdr;
-	unsigned long n;
+	unsigned long n, i;
 	int ret, offset;
 
 	if (!sev_guest(kvm))
@@ -863,6 +860,12 @@ static int sev_launch_secret(struct kvm *kvm, struct kvm_sev_cmd *argp)
 	if (!pages)
 		return -ENOMEM;
 
+	/*
+	 * Flush (on non-coherent CPUs) before LAUNCH_SECRET encrypts pages in
+	 * place, the cache may contain data that was written unencrypted.
+	 */
+	sev_clflush_pages(pages, n);
+
 	/*
 	 * The secret must be copied into contiguous memory region, lets verify
 	 * that userspace memory pages are contiguous before we issue command.
@@ -908,6 +911,11 @@ static int sev_launch_secret(struct kvm *kvm, struct kvm_sev_cmd *argp)
 e_free:
 	kfree(data);
 e_unpin_memory:
+	/* content of memory is updated, mark pages dirty */
+	for (i = 0; i < n; i++) {
+		set_page_dirty_lock(pages[i]);
+		mark_page_accessed(pages[i]);
+	}
 	sev_unpin_memory(kvm, pages, n);
 	return ret;
 }
-- 
2.28.0.681.g6f77f65b4e-goog