arch/arm64/kernel/alternative.c - linux - Git at Google

 // 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)->cpufeature & ~ARM64_CB_BIT)
 #define ALT_HAS_CB(a)		((a)->cpufeature & 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 cpufeature)
 {
 	if (WARN_ON(cpufeature >= ARM64_NCAPS))
 		return false;

 	return test_bit(cpufeature, 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 void clean_dcache_range_nopatch(u64 start, u64 end)
 {
 	u64 cur, d_size, ctr_el0;

 	ctr_el0 = read_sanitised_ftr_reg(SYS_CTR_EL0);
 	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 *feature_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, feature_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();

 		/* Ignore ARM64_CB bit from feature mask */
 		bitmap_or(applied_alternatives, applied_alternatives,
 			  feature_mask, ARM64_NCAPS);
 		bitmap_and(applied_alternatives, applied_alternatives,
 			   cpu_hwcaps, ARM64_NCAPS);
 	}
 }

 void 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 = {
 	.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 __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_capabilities,
 				  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_capabilities[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);
	// 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)->cpufeature & ~ARM64_CB_BIT)
	#define ALT_HAS_CB(a) ((a)->cpufeature & 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 cpufeature)
	{
	if (WARN_ON(cpufeature >= ARM64_NCAPS))
	return false;

	return test_bit(cpufeature, 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 void clean_dcache_range_nopatch(u64 start, u64 end)
	{
	u64 cur, d_size, ctr_el0;

	ctr_el0 = read_sanitised_ftr_reg(SYS_CTR_EL0);
	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 *feature_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, feature_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();

	/* Ignore ARM64_CB bit from feature mask */
	bitmap_or(applied_alternatives, applied_alternatives,
	feature_mask, ARM64_NCAPS);
	bitmap_and(applied_alternatives, applied_alternatives,
	cpu_hwcaps, ARM64_NCAPS);
	}
	}

	void 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 = {
	.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 __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_capabilities,
	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_capabilities[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);