[tip: x86/seves] x86/sev-es: Handle string port IO to kernel memory properly

[tip-bot2 for Hyunwook (Wooky) Baek]

The following commit has been merged into the x86/seves branch of tip:

Commit-ID:     36648d64ac3420b3cfa741b12b14633fad9651e4
Gitweb:        https://git.kernel.org/tip/36648d64ac3420b3cfa741b12b14633fad9651e4
Author:        Hyunwook (Wooky) Baek <baekhw@xxxxxxxxxx>
AuthorDate:    Sat, 09 Jan 2021 23:11:02 -08:00
Committer:     Borislav Petkov <bp@xxxxxxx>
CommitterDate: Mon, 11 Jan 2021 12:22:10 +01:00

x86/sev-es: Handle string port IO to kernel memory properly

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. ]

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
---
 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 0bd1a0f..ab31c34 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(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 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))