x86/sev: Check for user-space IOIO pointing to kernel space

Check the memory operand of INS/OUTS before emulating the instruction.
The #VC exception can get raised from user-space, but the memory operand
can be manipulated to access kernel memory before the emulation actually
begins and after the exception handler has run.

  [ bp: Massage commit message. ]

Fixes: 597cfe48 ("x86/boot/compressed/64: Setup a GHCB-based VC Exception handler")
Reported-by: Tom Dohrmann <erbse.13@gmx.de>
Signed-off-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Cc: <stable@kernel.org>

arch/x86/boot/compressed/sev.c

@@ -108,6 +108,11 @@ static enum es_result vc_ioio_check(struct es_em_ctxt *ctxt, u16 port, size_t si
 	return ES_OK;
 }
 
+static bool fault_in_kernel_space(unsigned long address)
+{
+	return false;
+}
+
 #undef __init
 #define __init
 

arch/x86/kernel/sev-shared.c

@@ -592,6 +592,23 @@ void __init do_vc_no_ghcb(struct pt_regs *regs, unsigned long exit_code)
 	sev_es_terminate(SEV_TERM_SET_GEN, GHCB_SEV_ES_GEN_REQ);
 }
 
+static enum es_result vc_insn_string_check(struct es_em_ctxt *ctxt,
+					   unsigned long address,
+					   bool write)
+{
+	if (user_mode(ctxt->regs) && fault_in_kernel_space(address)) {
+		ctxt->fi.vector     = X86_TRAP_PF;
+		ctxt->fi.error_code = X86_PF_USER;
+		ctxt->fi.cr2        = address;
+		if (write)
+			ctxt->fi.error_code |= X86_PF_WRITE;
+
+		return ES_EXCEPTION;
+	}
+
+	return ES_OK;
+}
+
 static enum es_result vc_insn_string_read(struct es_em_ctxt *ctxt,
 					  void *src, char *buf,
 					  unsigned int data_size,
@@ -599,7 +616,12 @@ static enum es_result vc_insn_string_read(struct es_em_ctxt *ctxt,
 					  bool backwards)
 {
 	int i, b = backwards ? -1 : 1;
-	enum es_result ret = ES_OK;
+	unsigned long address = (unsigned long)src;
+	enum es_result ret;
+
+	ret = vc_insn_string_check(ctxt, address, false);
+	if (ret != ES_OK)
+		return ret;
 
 	for (i = 0; i < count; i++) {
 		void *s = src + (i * data_size * b);
@@ -620,7 +642,12 @@ static enum es_result vc_insn_string_write(struct es_em_ctxt *ctxt,
 					   bool backwards)
 {
 	int i, s = backwards ? -1 : 1;
-	enum es_result ret = ES_OK;
+	unsigned long address = (unsigned long)dst;
+	enum es_result ret;
+
+	ret = vc_insn_string_check(ctxt, address, true);
+	if (ret != ES_OK)
+		return ret;
 
 	for (i = 0; i < count; i++) {
 		void *d = dst + (i * data_size * s);