1 files changed, 321 insertions, 0 deletions
diff --git a/arch/arm64/kernel/idreg-override.c b/arch/arm64/kernel/idreg-override.c
new file mode 100644
index 000000000..95133765e
--- /dev/null
+++ b/arch/arm64/kernel/idreg-override.c
@@ -0,0 +1,321 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Early cpufeature override framework
+ *
+ * Copyright (C) 2020 Google LLC
+ * Author: Marc Zyngier <maz@kernel.org>
+ */
+
+#include <linux/ctype.h>
+#include <linux/kernel.h>
+#include <linux/libfdt.h>
+
+#include <asm/cacheflush.h>
+#include <asm/cpufeature.h>
+#include <asm/setup.h>
+
+#define FTR_DESC_NAME_LEN	20
+#define FTR_DESC_FIELD_LEN	10
+#define FTR_ALIAS_NAME_LEN	30
+#define FTR_ALIAS_OPTION_LEN	116
+
+static u64 __boot_status __initdata;
+
+struct ftr_set_desc {
+	char 				name[FTR_DESC_NAME_LEN];
+	struct arm64_ftr_override	*override;
+	struct {
+		char			name[FTR_DESC_FIELD_LEN];
+		u8			shift;
+		u8			width;
+		bool			(*filter)(u64 val);
+	} 				fields[];
+};
+
+#define FIELD(n, s, f)	{ .name = n, .shift = s, .width = 4, .filter = f }
+
+static bool __init mmfr1_vh_filter(u64 val)
+{
+	/*
+	 * If we ever reach this point while running VHE, we're
+	 * guaranteed to be on one of these funky, VHE-stuck CPUs. If
+	 * the user was trying to force nVHE on us, proceed with
+	 * attitude adjustment.
+	 */
+	return !(__boot_status == (BOOT_CPU_FLAG_E2H | BOOT_CPU_MODE_EL2) &&
+		 val == 0);
+}
+
+static const struct ftr_set_desc mmfr1 __initconst = {
+	.name		= "id_aa64mmfr1",
+	.override	= &id_aa64mmfr1_override,
+	.fields		= {
+		FIELD("vh", ID_AA64MMFR1_EL1_VH_SHIFT, mmfr1_vh_filter),
+		{}
+	},
+};
+
+static bool __init pfr0_sve_filter(u64 val)
+{
+	/*
+	 * Disabling SVE also means disabling all the features that
+	 * are associated with it. The easiest way to do it is just to
+	 * override id_aa64zfr0_el1 to be 0.
+	 */
+	if (!val) {
+		id_aa64zfr0_override.val = 0;
+		id_aa64zfr0_override.mask = GENMASK(63, 0);
+	}
+
+	return true;
+}
+
+static const struct ftr_set_desc pfr0 __initconst = {
+	.name		= "id_aa64pfr0",
+	.override	= &id_aa64pfr0_override,
+	.fields		= {
+	        FIELD("sve", ID_AA64PFR0_EL1_SVE_SHIFT, pfr0_sve_filter),
+		{}
+	},
+};
+
+static bool __init pfr1_sme_filter(u64 val)
+{
+	/*
+	 * Similarly to SVE, disabling SME also means disabling all
+	 * the features that are associated with it. Just set
+	 * id_aa64smfr0_el1 to 0 and don't look back.
+	 */
+	if (!val) {
+		id_aa64smfr0_override.val = 0;
+		id_aa64smfr0_override.mask = GENMASK(63, 0);
+	}
+
+	return true;
+}
+
+static const struct ftr_set_desc pfr1 __initconst = {
+	.name		= "id_aa64pfr1",
+	.override	= &id_aa64pfr1_override,
+	.fields		= {
+		FIELD("bt", ID_AA64PFR1_EL1_BT_SHIFT, NULL ),
+		FIELD("mte", ID_AA64PFR1_EL1_MTE_SHIFT, NULL),
+		FIELD("sme", ID_AA64PFR1_EL1_SME_SHIFT, pfr1_sme_filter),
+		{}
+	},
+};
+
+static const struct ftr_set_desc isar1 __initconst = {
+	.name		= "id_aa64isar1",
+	.override	= &id_aa64isar1_override,
+	.fields		= {
+		FIELD("gpi", ID_AA64ISAR1_EL1_GPI_SHIFT, NULL),
+		FIELD("gpa", ID_AA64ISAR1_EL1_GPA_SHIFT, NULL),
+		FIELD("api", ID_AA64ISAR1_EL1_API_SHIFT, NULL),
+		FIELD("apa", ID_AA64ISAR1_EL1_APA_SHIFT, NULL),
+		{}
+	},
+};
+
+static const struct ftr_set_desc isar2 __initconst = {
+	.name		= "id_aa64isar2",
+	.override	= &id_aa64isar2_override,
+	.fields		= {
+		FIELD("gpa3", ID_AA64ISAR2_EL1_GPA3_SHIFT, NULL),
+		FIELD("apa3", ID_AA64ISAR2_EL1_APA3_SHIFT, NULL),
+		{}
+	},
+};
+
+static const struct ftr_set_desc smfr0 __initconst = {
+	.name		= "id_aa64smfr0",
+	.override	= &id_aa64smfr0_override,
+	.fields		= {
+		/* FA64 is a one bit field... :-/ */
+		{ "fa64", ID_AA64SMFR0_EL1_FA64_SHIFT, 1, },
+		{}
+	},
+};
+
+extern struct arm64_ftr_override kaslr_feature_override;
+
+static const struct ftr_set_desc kaslr __initconst = {
+	.name		= "kaslr",
+#ifdef CONFIG_RANDOMIZE_BASE
+	.override	= &kaslr_feature_override,
+#endif
+	.fields		= {
+		FIELD("disabled", 0, NULL),
+		{}
+	},
+};
+
+static const struct ftr_set_desc * const regs[] __initconst = {
+	&mmfr1,
+	&pfr0,
+	&pfr1,
+	&isar1,
+	&isar2,
+	&smfr0,
+	&kaslr,
+};
+
+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" },
+	{ "arm64.nosve",		"id_aa64pfr0.sve=0 id_aa64pfr1.sme=0" },
+	{ "arm64.nosme",		"id_aa64pfr1.sme=0" },
+	{ "arm64.nobti",		"id_aa64pfr1.bt=0" },
+	{ "arm64.nopauth",
+	  "id_aa64isar1.gpi=0 id_aa64isar1.gpa=0 "
+	  "id_aa64isar1.api=0 id_aa64isar1.apa=0 "
+	  "id_aa64isar2.gpa3=0 id_aa64isar2.apa3=0"	   },
+	{ "arm64.nomte",		"id_aa64pfr1.mte=0" },
+	{ "nokaslr",			"kaslr.disabled=1" },
+};
+
+static int __init find_field(const char *cmdline,
+			     const struct ftr_set_desc *reg, int f, u64 *v)
+{
+	char opt[FTR_DESC_NAME_LEN + FTR_DESC_FIELD_LEN + 2];
+	int len;
+
+	len = snprintf(opt, ARRAY_SIZE(opt), "%s.%s=",
+		       reg->name, reg->fields[f].name);
+
+	if (!parameqn(cmdline, opt, len))
+		return -1;
+
+	return kstrtou64(cmdline + len, 0, v);
+}
+
+static void __init match_options(const char *cmdline)
+{
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(regs); i++) {
+		int f;
+
+		if (!regs[i]->override)
+			continue;
+
+		for (f = 0; strlen(regs[i]->fields[f].name); f++) {
+			u64 shift = regs[i]->fields[f].shift;
+			u64 width = regs[i]->fields[f].width ?: 4;
+			u64 mask = GENMASK_ULL(shift + width - 1, shift);
+			u64 v;
+
+			if (find_field(cmdline, regs[i], f, &v))
+				continue;
+
+			/*
+			 * If an override gets filtered out, advertise
+			 * it by setting the value to the all-ones while
+			 * clearing the mask... Yes, this is fragile.
+			 */
+			if (regs[i]->fields[f].filter &&
+			    !regs[i]->fields[f].filter(v)) {
+				regs[i]->override->val  |= mask;
+				regs[i]->override->mask &= ~mask;
+				continue;
+			}
+
+			regs[i]->override->val  &= ~mask;
+			regs[i]->override->val  |= (v << shift) & mask;
+			regs[i]->override->mask |= mask;
+
+			return;
+		}
+	}
+}
+
+static __init void __parse_cmdline(const char *cmdline, bool parse_aliases)
+{
+	do {
+		char buf[256];
+		size_t len;
+		int i;
+
+		cmdline = skip_spaces(cmdline);
+
+		for (len = 0; cmdline[len] && !isspace(cmdline[len]); len++);
+		if (!len)
+			return;
+
+		len = min(len, ARRAY_SIZE(buf) - 1);
+		strncpy(buf, cmdline, len);
+		buf[len] = 0;
+
+		if (strcmp(buf, "--") == 0)
+			return;
+
+		cmdline += len;
+
+		match_options(buf);
+
+		for (i = 0; parse_aliases && i < ARRAY_SIZE(aliases); i++)
+			if (parameq(buf, aliases[i].alias))
+				__parse_cmdline(aliases[i].feature, false);
+	} while (1);
+}
+
+static __init const u8 *get_bootargs_cmdline(void)
+{
+	const u8 *prop;
+	void *fdt;
+	int node;
+
+	fdt = get_early_fdt_ptr();
+	if (!fdt)
+		return NULL;
+
+	node = fdt_path_offset(fdt, "/chosen");
+	if (node < 0)
+		return NULL;
+
+	prop = fdt_getprop(fdt, node, "bootargs", NULL);
+	if (!prop)
+		return NULL;
+
+	return strlen(prop) ? prop : NULL;
+}
+
+static __init void parse_cmdline(void)
+{
+	const u8 *prop = get_bootargs_cmdline();
+
+	if (IS_ENABLED(CONFIG_CMDLINE_FORCE) || !prop)
+		__parse_cmdline(CONFIG_CMDLINE, true);
+
+	if (!IS_ENABLED(CONFIG_CMDLINE_FORCE) && prop)
+		__parse_cmdline(prop, true);
+}
+
+/* Keep checkers quiet */
+void init_feature_override(u64 boot_status);
+
+asmlinkage void __init init_feature_override(u64 boot_status)
+{
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(regs); i++) {
+		if (regs[i]->override) {
+			regs[i]->override->val  = 0;
+			regs[i]->override->mask = 0;
+		}
+	}
+
+	__boot_status = boot_status;
+
+	parse_cmdline();
+
+	for (i = 0; i < ARRAY_SIZE(regs); i++) {
+		if (regs[i]->override)
+			dcache_clean_inval_poc((unsigned long)regs[i]->override,
+					    (unsigned long)regs[i]->override +
+					    sizeof(*regs[i]->override));
+	}
+}