1 files changed, 300 insertions, 0 deletions
diff --git a/arch/arm64/kernel/alternative.c b/arch/arm64/kernel/alternative.c
new file mode 100644
index 000000000..8ff6610af
--- /dev/null
+++ b/arch/arm64/kernel/alternative.c
@@ -0,0 +1,300 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * alternative runtime patching
+ * inspired by the x86 version
+ *
+ * Copyright (C) 2014 ARM Ltd.
+ */
+
+#define pr_fmt(fmt) "alternatives: " fmt
+
+#include <linux/init.h>
+#include <linux/cpu.h>
+#include <linux/elf.h>
+#include <asm/cacheflush.h>
+#include <asm/alternative.h>
+#include <asm/cpufeature.h>
+#include <asm/insn.h>
+#include <asm/module.h>
+#include <asm/sections.h>
+#include <asm/vdso.h>
+#include <linux/stop_machine.h>
+
+#define __ALT_PTR(a, f)		((void *)&(a)->f + (a)->f)
+#define ALT_ORIG_PTR(a)		__ALT_PTR(a, orig_offset)
+#define ALT_REPL_PTR(a)		__ALT_PTR(a, alt_offset)
+
+#define ALT_CAP(a)		((a)->cpucap & ~ARM64_CB_BIT)
+#define ALT_HAS_CB(a)		((a)->cpucap & ARM64_CB_BIT)
+
+/* Volatile, as we may be patching the guts of READ_ONCE() */
+static volatile int all_alternatives_applied;
+
+static DECLARE_BITMAP(applied_alternatives, ARM64_NCAPS);
+
+struct alt_region {
+	struct alt_instr *begin;
+	struct alt_instr *end;
+};
+
+bool alternative_is_applied(u16 cpucap)
+{
+	if (WARN_ON(cpucap >= ARM64_NCAPS))
+		return false;
+
+	return test_bit(cpucap, applied_alternatives);
+}
+
+/*
+ * Check if the target PC is within an alternative block.
+ */
+static __always_inline bool branch_insn_requires_update(struct alt_instr *alt, unsigned long pc)
+{
+	unsigned long replptr = (unsigned long)ALT_REPL_PTR(alt);
+	return !(pc >= replptr && pc <= (replptr + alt->alt_len));
+}
+
+#define align_down(x, a)	((unsigned long)(x) & ~(((unsigned long)(a)) - 1))
+
+static __always_inline u32 get_alt_insn(struct alt_instr *alt, __le32 *insnptr, __le32 *altinsnptr)
+{
+	u32 insn;
+
+	insn = le32_to_cpu(*altinsnptr);
+
+	if (aarch64_insn_is_branch_imm(insn)) {
+		s32 offset = aarch64_get_branch_offset(insn);
+		unsigned long target;
+
+		target = (unsigned long)altinsnptr + offset;
+
+		/*
+		 * If we're branching inside the alternate sequence,
+		 * do not rewrite the instruction, as it is already
+		 * correct. Otherwise, generate the new instruction.
+		 */
+		if (branch_insn_requires_update(alt, target)) {
+			offset = target - (unsigned long)insnptr;
+			insn = aarch64_set_branch_offset(insn, offset);
+		}
+	} else if (aarch64_insn_is_adrp(insn)) {
+		s32 orig_offset, new_offset;
+		unsigned long target;
+
+		/*
+		 * If we're replacing an adrp instruction, which uses PC-relative
+		 * immediate addressing, adjust the offset to reflect the new
+		 * PC. adrp operates on 4K aligned addresses.
+		 */
+		orig_offset  = aarch64_insn_adrp_get_offset(insn);
+		target = align_down(altinsnptr, SZ_4K) + orig_offset;
+		new_offset = target - align_down(insnptr, SZ_4K);
+		insn = aarch64_insn_adrp_set_offset(insn, new_offset);
+	} else if (aarch64_insn_uses_literal(insn)) {
+		/*
+		 * Disallow patching unhandled instructions using PC relative
+		 * literal addresses
+		 */
+		BUG();
+	}
+
+	return insn;
+}
+
+static noinstr void patch_alternative(struct alt_instr *alt,
+			      __le32 *origptr, __le32 *updptr, int nr_inst)
+{
+	__le32 *replptr;
+	int i;
+
+	replptr = ALT_REPL_PTR(alt);
+	for (i = 0; i < nr_inst; i++) {
+		u32 insn;
+
+		insn = get_alt_insn(alt, origptr + i, replptr + i);
+		updptr[i] = cpu_to_le32(insn);
+	}
+}
+
+/*
+ * We provide our own, private D-cache cleaning function so that we don't
+ * accidentally call into the cache.S code, which is patched by us at
+ * runtime.
+ */
+static noinstr void clean_dcache_range_nopatch(u64 start, u64 end)
+{
+	u64 cur, d_size, ctr_el0;
+
+	ctr_el0 = arm64_ftr_reg_ctrel0.sys_val;
+	d_size = 4 << cpuid_feature_extract_unsigned_field(ctr_el0,
+							   CTR_EL0_DminLine_SHIFT);
+	cur = start & ~(d_size - 1);
+	do {
+		/*
+		 * We must clean+invalidate to the PoC in order to avoid
+		 * Cortex-A53 errata 826319, 827319, 824069 and 819472
+		 * (this corresponds to ARM64_WORKAROUND_CLEAN_CACHE)
+		 */
+		asm volatile("dc civac, %0" : : "r" (cur) : "memory");
+	} while (cur += d_size, cur < end);
+}
+
+static void __apply_alternatives(const struct alt_region *region,
+				 bool is_module,
+				 unsigned long *cpucap_mask)
+{
+	struct alt_instr *alt;
+	__le32 *origptr, *updptr;
+	alternative_cb_t alt_cb;
+
+	for (alt = region->begin; alt < region->end; alt++) {
+		int nr_inst;
+		int cap = ALT_CAP(alt);
+
+		if (!test_bit(cap, cpucap_mask))
+			continue;
+
+		if (!cpus_have_cap(cap))
+			continue;
+
+		if (ALT_HAS_CB(alt))
+			BUG_ON(alt->alt_len != 0);
+		else
+			BUG_ON(alt->alt_len != alt->orig_len);
+
+		origptr = ALT_ORIG_PTR(alt);
+		updptr = is_module ? origptr : lm_alias(origptr);
+		nr_inst = alt->orig_len / AARCH64_INSN_SIZE;
+
+		if (ALT_HAS_CB(alt))
+			alt_cb  = ALT_REPL_PTR(alt);
+		else
+			alt_cb = patch_alternative;
+
+		alt_cb(alt, origptr, updptr, nr_inst);
+
+		if (!is_module) {
+			clean_dcache_range_nopatch((u64)origptr,
+						   (u64)(origptr + nr_inst));
+		}
+	}
+
+	/*
+	 * The core module code takes care of cache maintenance in
+	 * flush_module_icache().
+	 */
+	if (!is_module) {
+		dsb(ish);
+		icache_inval_all_pou();
+		isb();
+
+		bitmap_or(applied_alternatives, applied_alternatives,
+			  cpucap_mask, ARM64_NCAPS);
+		bitmap_and(applied_alternatives, applied_alternatives,
+			   system_cpucaps, ARM64_NCAPS);
+	}
+}
+
+static void __init apply_alternatives_vdso(void)
+{
+	struct alt_region region;
+	const struct elf64_hdr *hdr;
+	const struct elf64_shdr *shdr;
+	const struct elf64_shdr *alt;
+	DECLARE_BITMAP(all_capabilities, ARM64_NCAPS);
+
+	bitmap_fill(all_capabilities, ARM64_NCAPS);
+
+	hdr = (struct elf64_hdr *)vdso_start;
+	shdr = (void *)hdr + hdr->e_shoff;
+	alt = find_section(hdr, shdr, ".altinstructions");
+	if (!alt)
+		return;
+
+	region = (struct alt_region){
+		.begin	= (void *)hdr + alt->sh_offset,
+		.end	= (void *)hdr + alt->sh_offset + alt->sh_size,
+	};
+
+	__apply_alternatives(&region, false, &all_capabilities[0]);
+}
+
+static const struct alt_region kernel_alternatives __initconst = {
+	.begin	= (struct alt_instr *)__alt_instructions,
+	.end	= (struct alt_instr *)__alt_instructions_end,
+};
+
+/*
+ * We might be patching the stop_machine state machine, so implement a
+ * really simple polling protocol here.
+ */
+static int __init __apply_alternatives_multi_stop(void *unused)
+{
+	/* We always have a CPU 0 at this point (__init) */
+	if (smp_processor_id()) {
+		while (!all_alternatives_applied)
+			cpu_relax();
+		isb();
+	} else {
+		DECLARE_BITMAP(remaining_capabilities, ARM64_NCAPS);
+
+		bitmap_complement(remaining_capabilities, boot_cpucaps,
+				  ARM64_NCAPS);
+
+		BUG_ON(all_alternatives_applied);
+		__apply_alternatives(&kernel_alternatives, false,
+				     remaining_capabilities);
+		/* Barriers provided by the cache flushing */
+		all_alternatives_applied = 1;
+	}
+
+	return 0;
+}
+
+void __init apply_alternatives_all(void)
+{
+	pr_info("applying system-wide alternatives\n");
+
+	apply_alternatives_vdso();
+	/* better not try code patching on a live SMP system */
+	stop_machine(__apply_alternatives_multi_stop, NULL, cpu_online_mask);
+}
+
+/*
+ * 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.
+ */
+void __init apply_boot_alternatives(void)
+{
+	/* If called on non-boot cpu things could go wrong */
+	WARN_ON(smp_processor_id() != 0);
+
+	pr_info("applying boot alternatives\n");
+
+	__apply_alternatives(&kernel_alternatives, false,
+			     &boot_cpucaps[0]);
+}
+
+#ifdef CONFIG_MODULES
+void apply_alternatives_module(void *start, size_t length)
+{
+	struct alt_region region = {
+		.begin	= start,
+		.end	= start + length,
+	};
+	DECLARE_BITMAP(all_capabilities, ARM64_NCAPS);
+
+	bitmap_fill(all_capabilities, ARM64_NCAPS);
+
+	__apply_alternatives(&region, true, &all_capabilities[0]);
+}
+#endif
+
+noinstr void alt_cb_patch_nops(struct alt_instr *alt, __le32 *origptr,
+			       __le32 *updptr, int nr_inst)
+{
+	for (int i = 0; i < nr_inst; i++)
+		updptr[i] = cpu_to_le32(aarch64_insn_gen_nop());
+}
+EXPORT_SYMBOL(alt_cb_patch_nops);