[Part2 PATCH v4 22/29] KVM: SVM: Add support for SEV DEBUG_ENCRYPT command

[Brijesh Singh]

The command copies a plaintext into guest memory and encrypts it using
the VM encryption key. The command will be used for debug purposes
(e.g setting breakpoints through gdbserver)

Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Cc: "Radim KrÄmÃÅ" <rkrcmar@xxxxxxxxxx>
Cc: Joerg Roedel <joro@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxx>
Cc: Tom Lendacky <thomas.lendacky@xxxxxxx>
Cc: x86@xxxxxxxxxx
Cc: kvm@xxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Signed-off-by: Brijesh Singh <brijesh.singh@xxxxxxx>
---
 arch/x86/kvm/svm.c | 132 +++++++++++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 124 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 4d51ccb462db..16b338d9dc87 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -6203,6 +6203,104 @@ static int __sev_dbg_decrypt(struct kvm *kvm, unsigned long paddr,
 	return ret;
 }
 
+static int __sev_dbg_encrypt(struct kvm *kvm, unsigned long __user vaddr,
+			     unsigned long paddr, unsigned long __user dst_vaddr,
+			     unsigned long dst_paddr, int size, int *error)
+{
+	struct page *src_tpage = NULL;
+	struct page *dst_tpage = NULL;
+	int ret, len = size;
+
+	/*
+	 *  If source buffer is not 16-byte aligned then we copy the data from
+	 *  source buffer into a PAGE aligned intermediate (src_tpage) buffer
+	 *  and use this intermediate buffer as source buffer.
+	 */
+	if (!IS_ALIGNED(vaddr, 16)) {
+		src_tpage = alloc_page(GFP_KERNEL);
+		if (!src_tpage)
+			return -ENOMEM;
+
+		if (copy_from_user(page_address(src_tpage),
+			(void __user *)(uintptr_t)vaddr, size)) {
+			__free_page(src_tpage);
+			return -EFAULT;
+		}
+		paddr = __sme_page_pa(src_tpage);
+
+		/* flush the caches to ensure that DRAM has recent contents */
+		clflush_cache_range(page_address(src_tpage), PAGE_SIZE);
+	}
+
+	/*
+	 *  If destination buffer or length is not 16-byte aligned then:
+	 *   - decrypt portion of destination buffer into intermediate buffer
+	 *     (dst_tpage)
+	 *   - copy the source data into intermediate buffer
+	 *   - use the intermediate buffer as source buffer
+	 */
+	if (!IS_ALIGNED(dst_vaddr, 16) ||
+	    !IS_ALIGNED(size, 16)) {
+		int dst_offset;
+
+		dst_tpage = alloc_page(GFP_KERNEL);
+		if (!dst_tpage) {
+			ret = -ENOMEM;
+			goto e_free;
+		}
+
+		/* decrypt destination buffer into intermediate buffer */
+		ret = __sev_dbg_decrypt(kvm,
+					round_down(dst_paddr, 16),
+					0,
+					(unsigned long)page_address(dst_tpage),
+					__sme_page_pa(dst_tpage),
+					round_up(size, 16),
+					error);
+		if (ret)
+			goto e_free;
+
+		dst_offset = dst_paddr & 15;
+
+		/*
+		 * modify the intermediate buffer with data from source buffer.
+		 */
+		if (src_tpage)
+			memcpy(page_address(dst_tpage) + dst_offset,
+			       page_address(src_tpage), size);
+		else {
+			if (copy_from_user(page_address(dst_tpage) + dst_offset,
+					   (void __user *)(uintptr_t)vaddr, size)) {
+				ret = -EFAULT;
+				goto e_free;
+			}
+		}
+
+
+		/* use intermediate buffer as source */
+		paddr = __sme_page_pa(dst_tpage);
+
+		/*
+		 * Cache accesses between x86 and PSP are not coherent. Lets
+		 * flush the caches to ensure that we can get the updated contents.
+		 */
+		clflush_cache_range(page_address(dst_tpage), PAGE_SIZE);
+
+		/* now we have length and destination buffer aligned */
+		dst_paddr = round_down(dst_paddr, 16);
+		len = round_up(size, 16);
+	}
+
+	ret = __sev_issue_dbg_cmd(kvm, paddr, dst_paddr, len, error, true);
+
+e_free:
+	if (src_tpage)
+		__free_page(src_tpage);
+	if (dst_tpage)
+		__free_page(dst_tpage);
+	return ret;
+}
+
 static int sev_dbg_crypt(struct kvm *kvm, struct kvm_sev_cmd *argp, bool dec)
 {
 	unsigned long vaddr, vaddr_end, next_vaddr;
@@ -6240,9 +6338,10 @@ static int sev_dbg_crypt(struct kvm *kvm, struct kvm_sev_cmd *argp, bool dec)
 		}
 
 		/*
-		 * Cache access between te PSP and x86 are not coherent, hence we
-		 * flush the caches to buffers shared with PSP to ensure that we
-		 * will be able to see the PSP updates.
+		 * PSP will access the guest memory range with C=1, but hypervisor
+		 * cache may still be looking the memory with C=0, lets make sure
+		 * we flush the caches so that data gets accessed with correct C-bit
+		 * on both PSP and x86 side.
 		 */
 		sev_clflush_pages(src_p, 1);
 		sev_clflush_pages(dst_p, 1);
@@ -6255,11 +6354,19 @@ static int sev_dbg_crypt(struct kvm *kvm, struct kvm_sev_cmd *argp, bool dec)
 		d_off = dst_vaddr & ~PAGE_MASK;
 		len = min_t(size_t, (PAGE_SIZE - s_off), size);
 
-		ret = __sev_dbg_decrypt(kvm,
-				       __sme_page_pa(src_p[0]) + s_off,
-				       dst_vaddr, 0,
-				       __sme_page_pa(dst_p[0]) + d_off,
-				       len, &argp->error);
+		if (dec)
+			ret = __sev_dbg_decrypt(kvm,
+						__sme_page_pa(src_p[0]) + s_off,
+						dst_vaddr, 0,
+						__sme_page_pa(dst_p[0]) + d_off,
+						len, &argp->error);
+		else
+			ret = __sev_dbg_encrypt(kvm,
+						vaddr,
+						__sme_page_pa(src_p[0]) + s_off,
+						dst_vaddr,
+						__sme_page_pa(dst_p[0]) + d_off,
+						len, &argp->error);
 
 		sev_unpin_memory(kvm, src_p, 1);
 		sev_unpin_memory(kvm, dst_p, 1);
@@ -6280,6 +6387,11 @@ static int sev_dbg_decrypt(struct kvm *kvm, struct kvm_sev_cmd *argp)
 	return sev_dbg_crypt(kvm, argp, true);
 }
 
+static int sev_dbg_encrypt(struct kvm *kvm, struct kvm_sev_cmd *argp)
+{
+	return sev_dbg_crypt(kvm, argp, false);
+}
+
 static int svm_mem_enc_op(struct kvm *kvm, void __user *argp)
 {
 	struct kvm_sev_cmd sev_cmd;
@@ -6319,6 +6431,10 @@ static int svm_mem_enc_op(struct kvm *kvm, void __user *argp)
 		r = sev_dbg_decrypt(kvm, &sev_cmd);
 		break;
 	}
+	case KVM_SEV_DBG_ENCRYPT: {
+		r = sev_dbg_encrypt(kvm, &sev_cmd);
+		break;
+	}
 	default:
 		break;
 	}
-- 
2.9.5