1 files changed, 236 insertions, 0 deletions
diff --git a/arch/riscv/kernel/alternative.c b/arch/riscv/kernel/alternative.c
new file mode 100644
index 000000000000..0128b161bfda
--- /dev/null
+++ b/arch/riscv/kernel/alternative.c
@@ -0,0 +1,236 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * alternative runtime patching
+ * inspired by the ARM64 and x86 version
+ *
+ * Copyright (C) 2021 Sifive.
+ */
+
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/cpu.h>
+#include <linux/uaccess.h>
+#include <asm/alternative.h>
+#include <asm/module.h>
+#include <asm/sections.h>
+#include <asm/vdso.h>
+#include <asm/vendorid_list.h>
+#include <asm/sbi.h>
+#include <asm/csr.h>
+#include <asm/insn.h>
+#include <asm/patch.h>
+
+struct cpu_manufacturer_info_t {
+	unsigned long vendor_id;
+	unsigned long arch_id;
+	unsigned long imp_id;
+	void (*patch_func)(struct alt_entry *begin, struct alt_entry *end,
+				  unsigned long archid, unsigned long impid,
+				  unsigned int stage);
+};
+
+static void riscv_fill_cpu_mfr_info(struct cpu_manufacturer_info_t *cpu_mfr_info)
+{
+#ifdef CONFIG_RISCV_M_MODE
+	cpu_mfr_info->vendor_id = csr_read(CSR_MVENDORID);
+	cpu_mfr_info->arch_id = csr_read(CSR_MARCHID);
+	cpu_mfr_info->imp_id = csr_read(CSR_MIMPID);
+#else
+	cpu_mfr_info->vendor_id = sbi_get_mvendorid();
+	cpu_mfr_info->arch_id = sbi_get_marchid();
+	cpu_mfr_info->imp_id = sbi_get_mimpid();
+#endif
+
+	switch (cpu_mfr_info->vendor_id) {
+#ifdef CONFIG_ERRATA_ANDES
+	case ANDES_VENDOR_ID:
+		cpu_mfr_info->patch_func = andes_errata_patch_func;
+		break;
+#endif
+#ifdef CONFIG_ERRATA_SIFIVE
+	case SIFIVE_VENDOR_ID:
+		cpu_mfr_info->patch_func = sifive_errata_patch_func;
+		break;
+#endif
+#ifdef CONFIG_ERRATA_THEAD
+	case THEAD_VENDOR_ID:
+		cpu_mfr_info->patch_func = thead_errata_patch_func;
+		break;
+#endif
+	default:
+		cpu_mfr_info->patch_func = NULL;
+	}
+}
+
+static u32 riscv_instruction_at(void *p)
+{
+	u16 *parcel = p;
+
+	return (u32)parcel[0] | (u32)parcel[1] << 16;
+}
+
+static void riscv_alternative_fix_auipc_jalr(void *ptr, u32 auipc_insn,
+					     u32 jalr_insn, int patch_offset)
+{
+	u32 call[2] = { auipc_insn, jalr_insn };
+	s32 imm;
+
+	/* get and adjust new target address */
+	imm = riscv_insn_extract_utype_itype_imm(auipc_insn, jalr_insn);
+	imm -= patch_offset;
+
+	/* update instructions */
+	riscv_insn_insert_utype_itype_imm(&call[0], &call[1], imm);
+
+	/* patch the call place again */
+	patch_text_nosync(ptr, call, sizeof(u32) * 2);
+}
+
+static void riscv_alternative_fix_jal(void *ptr, u32 jal_insn, int patch_offset)
+{
+	s32 imm;
+
+	/* get and adjust new target address */
+	imm = riscv_insn_extract_jtype_imm(jal_insn);
+	imm -= patch_offset;
+
+	/* update instruction */
+	riscv_insn_insert_jtype_imm(&jal_insn, imm);
+
+	/* patch the call place again */
+	patch_text_nosync(ptr, &jal_insn, sizeof(u32));
+}
+
+void riscv_alternative_fix_offsets(void *alt_ptr, unsigned int len,
+				      int patch_offset)
+{
+	int num_insn = len / sizeof(u32);
+	int i;
+
+	for (i = 0; i < num_insn; i++) {
+		u32 insn = riscv_instruction_at(alt_ptr + i * sizeof(u32));
+
+		/*
+		 * May be the start of an auipc + jalr pair
+		 * Needs to check that at least one more instruction
+		 * is in the list.
+		 */
+		if (riscv_insn_is_auipc(insn) && i < num_insn - 1) {
+			u32 insn2 = riscv_instruction_at(alt_ptr + (i + 1) * sizeof(u32));
+
+			if (!riscv_insn_is_jalr(insn2))
+				continue;
+
+			/* if instruction pair is a call, it will use the ra register */
+			if (RV_EXTRACT_RD_REG(insn) != 1)
+				continue;
+
+			riscv_alternative_fix_auipc_jalr(alt_ptr + i * sizeof(u32),
+							 insn, insn2, patch_offset);
+			i++;
+		}
+
+		if (riscv_insn_is_jal(insn)) {
+			s32 imm = riscv_insn_extract_jtype_imm(insn);
+
+			/* Don't modify jumps inside the alternative block */
+			if ((alt_ptr + i * sizeof(u32) + imm) >= alt_ptr &&
+			    (alt_ptr + i * sizeof(u32) + imm) < (alt_ptr + len))
+				continue;
+
+			riscv_alternative_fix_jal(alt_ptr + i * sizeof(u32),
+						  insn, patch_offset);
+		}
+	}
+}
+
+/*
+ * This is called very early in the boot process (directly after we run
+ * a feature detect on the boot CPU). No need to worry about other CPUs
+ * here.
+ */
+static void __init_or_module _apply_alternatives(struct alt_entry *begin,
+						 struct alt_entry *end,
+						 unsigned int stage)
+{
+	struct cpu_manufacturer_info_t cpu_mfr_info;
+
+	riscv_fill_cpu_mfr_info(&cpu_mfr_info);
+
+	riscv_cpufeature_patch_func(begin, end, stage);
+
+	if (!cpu_mfr_info.patch_func)
+		return;
+
+	cpu_mfr_info.patch_func(begin, end,
+				cpu_mfr_info.arch_id,
+				cpu_mfr_info.imp_id,
+				stage);
+}
+
+#ifdef CONFIG_MMU
+static void __init apply_vdso_alternatives(void)
+{
+	const Elf_Ehdr *hdr;
+	const Elf_Shdr *shdr;
+	const Elf_Shdr *alt;
+	struct alt_entry *begin, *end;
+
+	hdr = (Elf_Ehdr *)vdso_start;
+	shdr = (void *)hdr + hdr->e_shoff;
+	alt = find_section(hdr, shdr, ".alternative");
+	if (!alt)
+		return;
+
+	begin = (void *)hdr + alt->sh_offset,
+	end = (void *)hdr + alt->sh_offset + alt->sh_size,
+
+	_apply_alternatives((struct alt_entry *)begin,
+			    (struct alt_entry *)end,
+			    RISCV_ALTERNATIVES_BOOT);
+}
+#else
+static void __init apply_vdso_alternatives(void) { }
+#endif
+
+void __init apply_boot_alternatives(void)
+{
+	/* If called on non-boot cpu things could go wrong */
+	WARN_ON(smp_processor_id() != 0);
+
+	_apply_alternatives((struct alt_entry *)__alt_start,
+			    (struct alt_entry *)__alt_end,
+			    RISCV_ALTERNATIVES_BOOT);
+
+	apply_vdso_alternatives();
+}
+
+/*
+ * apply_early_boot_alternatives() is called from setup_vm() with MMU-off.
+ *
+ * Following requirements should be honoured for it to work correctly:
+ * 1) It should use PC-relative addressing for accessing kernel symbols.
+ *    To achieve this we always use GCC cmodel=medany.
+ * 2) The compiler instrumentation for FTRACE will not work for setup_vm()
+ *    so disable compiler instrumentation when FTRACE is enabled.
+ *
+ * Currently, the above requirements are honoured by using custom CFLAGS
+ * for alternative.o in kernel/Makefile.
+ */
+void __init apply_early_boot_alternatives(void)
+{
+#ifdef CONFIG_RISCV_ALTERNATIVE_EARLY
+	_apply_alternatives((struct alt_entry *)__alt_start,
+			    (struct alt_entry *)__alt_end,
+			    RISCV_ALTERNATIVES_EARLY_BOOT);
+#endif
+}
+
+#ifdef CONFIG_MODULES
+void apply_module_alternatives(void *start, size_t length)
+{
+	_apply_alternatives((struct alt_entry *)start,
+			    (struct alt_entry *)(start + length),
+			    RISCV_ALTERNATIVES_MODULE);
+}
+#endif