arm64: idreg-override: Avoid parameq() and parameqn()

The only way parameq() and parameqn() deviate from the ordinary string
and memory routines is that they ignore the difference between dashes
and underscores.

Since we copy each command line argument into a buffer before passing it
to parameq() and parameqn() numerous times, let's just convert all
dashes to underscores just once, and update the alias array accordingly.

This also helps reduce the dependency on kernel APIs that are no longer
available once we move this code into the early mini C runtime.
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20231129111555.3594833-59-ardb@google.comSigned-off-by: Will Deacon <will@kernel.org>

arch/arm64/kernel/idreg-override.c

@@ -185,8 +185,8 @@ static const struct {
 	char	alias[FTR_ALIAS_NAME_LEN];
 	char	feature[FTR_ALIAS_OPTION_LEN];
 } aliases[] __initconst = {
-	{ "kvm-arm.mode=nvhe",		"id_aa64mmfr1.vh=0" },
-	{ "kvm-arm.mode=protected",	"id_aa64mmfr1.vh=0" },
+	{ "kvm_arm.mode=nvhe",		"id_aa64mmfr1.vh=0" },
+	{ "kvm_arm.mode=protected",	"id_aa64mmfr1.vh=0" },
 	{ "arm64.nosve",		"id_aa64pfr0.sve=0" },
 	{ "arm64.nosme",		"id_aa64pfr1.sme=0" },
 	{ "arm64.nobti",		"id_aa64pfr1.bt=0" },
@@ -215,7 +215,7 @@ static int __init find_field(const char *cmdline,
 	len = snprintf(opt, ARRAY_SIZE(opt), "%s.%s=",
 		       reg->name, reg->fields[f].name);
 
-	if (!parameqn(cmdline, opt, len))
+	if (memcmp(cmdline, opt, len))
 		return -1;
 
 	return kstrtou64(cmdline + len, 0, v);
@@ -272,23 +272,29 @@ static __init void __parse_cmdline(const char *cmdline, bool parse_aliases)
 
 		cmdline = skip_spaces(cmdline);
 
-		for (len = 0; cmdline[len] && !isspace(cmdline[len]); len++);
-		if (!len)
+		/* terminate on "--" appearing on the command line by itself */
+		if (cmdline[0] == '-' && cmdline[1] == '-' && isspace(cmdline[2]))
 			return;
 
-		len = min(len, ARRAY_SIZE(buf) - 1);
-		memcpy(buf, cmdline, len);
-		buf[len] = '\0';
-
-		if (strcmp(buf, "--") == 0)
+		for (len = 0; cmdline[len] && !isspace(cmdline[len]); len++) {
+			if (len >= sizeof(buf) - 1)
+				break;
+			if (cmdline[len] == '-')
+				buf[len] = '_';
+			else
+				buf[len] = cmdline[len];
+		}
+		if (!len)
 			return;
 
+		buf[len] = 0;
+
 		cmdline += len;
 
 		match_options(buf);
 
 		for (i = 0; parse_aliases && i < ARRAY_SIZE(aliases); i++)
-			if (parameq(buf, aliases[i].alias))
+			if (!memcmp(buf, aliases[i].alias, len + 1))
 				__parse_cmdline(aliases[i].feature, false);
 	} while (1);
 }