[PATCH] x86/sev-es: Fix SEV-ES #VC handler for string port IO

[Hyunwook (Wooky) Baek]

Don't assume dest/source buffers are userspace addresses when manually
copying data for string I/O or MOVS MMIO, as {get,put}_user() will fail
if handed a kernel address and ultimately lead to a kernel panic.

Signed-off-by: Hyunwook (Wooky) Baek <baekhw@xxxxxxxxxx>
Acked-by: David Rientjes <rientjes@xxxxxxxxxx>
---
 arch/x86/kernel/sev-es.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/arch/x86/kernel/sev-es.c b/arch/x86/kernel/sev-es.c
index 0bd1a0fc587e..812494d216ba 100644
--- a/arch/x86/kernel/sev-es.c
+++ b/arch/x86/kernel/sev-es.c
@@ -286,6 +286,12 @@ static enum es_result vc_write_mem(struct es_em_ctxt *ctxt,
 	u16 d2;
 	u8  d1;
 
+	/* If instruction ran in kernel mode and the I/O buffer is in kernel space */
+	if (!user_mode(ctxt->regs) && !access_ok(s, size)) {
+		memcpy(dst, buf, size);
+		return ES_OK;
+	}
+
 	switch (size) {
 	case 1:
 		memcpy(&d1, buf, 1);
@@ -335,6 +341,12 @@ static enum es_result vc_read_mem(struct es_em_ctxt *ctxt,
 	u16 d2;
 	u8  d1;
 
+	/* If instruction ran in kernel mode and the I/O buffer is in kernel space */
+	if (!user_mode(ctxt->regs) && !access_ok(s, size)) {
+		memcpy(buf, src, size);
+		return ES_OK;
+	}
+
 	switch (size) {
 	case 1:
 		if (get_user(d1, s))
-- 
2.29.2.729.g45daf8777d-goog