[PATCH 5.10 191/199] x86/sev-es: Handle string port IO to kernel memory properly

[Greg Kroah-Hartman]

From: Hyunwook (Wooky) Baek <baekhw@xxxxxxxxxx>

commit 7024f60d655272bd2ca1d3a4c9e0a63319b1eea1 upstream.

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.

When invoking INSB/OUTSB instructions in kernel space in a
SEV-ES-enabled VM, the kernel crashes with the following message:

  "SEV-ES: Unsupported exception in #VC instruction emulation - can't continue"

Handle that case properly.

 [ bp: Massage commit message. ]

Fixes: f980f9c31a92 ("x86/sev-es: Compile early handler code into kernel image")
Signed-off-by: Hyunwook (Wooky) Baek <baekhw@xxxxxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Acked-by: David Rientjes <rientjes@xxxxxxxxxx>
Link: https://lkml.kernel.org/r/20210110071102.2576186-1-baekhw@xxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 arch/x86/kernel/sev-es.c |   12 ++++++++++++
 1 file changed, 12 insertions(+)

--- 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(struc
 	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(target, 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
 	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))