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Subject[Part2 PATCH v4 22/29] KVM: SVM: Add support for SEV DEBUG_ENCRYPT command
Date
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@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: "Radim Krčmář" <rkrcmar@redhat.com>
Cc: Joerg Roedel <joro@8bytes.org>
Cc: Borislav Petkov <bp@suse.de>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: x86@kernel.org
Cc: kvm@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
---
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
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