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. ]

Fixes: f980f9c31a92 ("x86/sev-es: Compile early handler code into kernel image")
Signed-off-by: Hyunwook (Wooky) Baek <baekhw@google.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Acked-by: David Rientjes <rientjes@google.com>
Link: https://lkml.kernel.org/r/20210110071102.2576186-1-baekhw@google.com

diff --git a/arch/x86/kernel/sev-es.c b/arch/x86/kernel/sev-es.c
index 0bd1a0f..ab31c34 100644 (file)
--- 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))