Re: [PATCH v1 11/19] x86/sev-es: Convert to insn_decode()

[Borislav Petkov]

On Fri, Dec 25, 2020 at 06:50:33PM +0800, kernel test robot wrote:
> If you fix the issue, kindly add following tag as appropriate
> Reported-by: kernel test robot <lkp@xxxxxxxxx>
> 
> All warnings (new ones prefixed by >>):
> 
> >> arch/x86/kernel/sev-es.c:258:7: warning: variable 'ret' is used uninitialized whenever 'if' condition is false [-Wsometimes-uninitialized]
>                    if (!insn_decode_regs(&ctxt->insn, ctxt->regs, buffer, res))
>                        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Yeah, good catch, thanks for reporting.

Frankly, the readability and "extensiblity" of that function can be
improved by splitting the two cases (diff ontop):

---
diff --git a/arch/x86/kernel/sev-es.c b/arch/x86/kernel/sev-es.c
index 564cc9fc693d..ea47037f1624 100644
--- a/arch/x86/kernel/sev-es.c
+++ b/arch/x86/kernel/sev-es.c
@@ -241,40 +241,53 @@ static int vc_fetch_insn_kernel(struct es_em_ctxt *ctxt,
 	return copy_from_kernel_nofault(buffer, (unsigned char *)ctxt->regs->ip, MAX_INSN_SIZE);
 }
 
-static enum es_result vc_decode_insn(struct es_em_ctxt *ctxt)
+static enum es_result __vc_decode_user_insn(struct es_em_ctxt *ctxt)
 {
 	char buffer[MAX_INSN_SIZE];
-	int res, ret;
-
-	if (user_mode(ctxt->regs)) {
-		res = insn_fetch_from_user(ctxt->regs, buffer);
-		if (!res) {
-			ctxt->fi.vector     = X86_TRAP_PF;
-			ctxt->fi.error_code = X86_PF_INSTR | X86_PF_USER;
-			ctxt->fi.cr2        = ctxt->regs->ip;
-			return ES_EXCEPTION;
-		}
+	int res;
 
-		if (!insn_decode_regs(&ctxt->insn, ctxt->regs, buffer, res))
-			return ES_DECODE_FAILED;
-	} else {
-		res = vc_fetch_insn_kernel(ctxt, buffer);
-		if (res) {
-			ctxt->fi.vector     = X86_TRAP_PF;
-			ctxt->fi.error_code = X86_PF_INSTR;
-			ctxt->fi.cr2        = ctxt->regs->ip;
-			return ES_EXCEPTION;
-		}
+	res = insn_fetch_from_user(ctxt->regs, buffer);
+	if (!res) {
+		ctxt->fi.vector     = X86_TRAP_PF;
+		ctxt->fi.error_code = X86_PF_INSTR | X86_PF_USER;
+		ctxt->fi.cr2        = ctxt->regs->ip;
+		return ES_EXCEPTION;
+	}
+
+	if (!insn_decode_regs(&ctxt->insn, ctxt->regs, buffer, res))
+		return ES_DECODE_FAILED;
+	else
+		return ES_OK;
+}
+
+static enum es_result __vc_decode_kern_insn(struct es_em_ctxt *ctxt)
+{
+	char buffer[MAX_INSN_SIZE];
+	int res;
 
-		ret = insn_decode(&ctxt->insn, buffer, MAX_INSN_SIZE - res, INSN_MODE_64);
+	res = vc_fetch_insn_kernel(ctxt, buffer);
+	if (res) {
+		ctxt->fi.vector     = X86_TRAP_PF;
+		ctxt->fi.error_code = X86_PF_INSTR;
+		ctxt->fi.cr2        = ctxt->regs->ip;
+		return ES_EXCEPTION;
 	}
 
-	if (ret < 0)
+	res = insn_decode(&ctxt->insn, buffer, MAX_INSN_SIZE - res, INSN_MODE_64);
+	if (res < 0)
 		return ES_DECODE_FAILED;
 	else
 		return ES_OK;
 }
 
+static enum es_result vc_decode_insn(struct es_em_ctxt *ctxt)
+{
+	if (user_mode(ctxt->regs))
+		return __vc_decode_user_insn(ctxt);
+	else
+		return __vc_decode_kern_insn(ctxt);
+}
+
 static enum es_result vc_write_mem(struct es_em_ctxt *ctxt,
 				   char *dst, char *buf, size_t size)
 {

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette