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

 /*
  * alternative runtime patching
  * inspired by the x86 version
  *
  * Copyright (C) 2014 ARM Ltd.
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 2 as
  * published by the Free Software Foundation.
  *
  * This program is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  */

 #define pr_fmt(fmt) "alternatives: " fmt

 #include <linux/init.h>
 #include <linux/cpu.h>
 #include <asm/cacheflush.h>
 #include <asm/alternative.h>
 #include <asm/cpufeature.h>
 #include <asm/insn.h>
 #include <asm/sections.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)

 int alternatives_applied;

 struct alt_region {
 	struct alt_instr *begin;
 	struct alt_instr *end;
 };

 /*
  * Check if the target PC is within an alternative block.
  */
 static bool branch_insn_requires_update(struct alt_instr *alt, unsigned long pc)
 {
 	unsigned long replptr;

 	if (kernel_text_address(pc))
 		return true;

 	replptr = (unsigned long)ALT_REPL_PTR(alt);
 	if (pc >= replptr && pc <= (replptr + alt->alt_len))
 		return false;

 	/*
 	 * Branching into *another* alternate sequence is doomed, and
 	 * we're not even trying to fix it up.
 	 */
 	BUG();
 }

 #define align_down(x, a)	((unsigned long)(x) & ~(((unsigned long)(a)) - 1))

 static 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 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_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(void *alt_region, bool is_module)
 {
 	struct alt_instr *alt;
 	struct alt_region *region = alt_region;
 	__le32 *origptr, *updptr;
 	alternative_cb_t alt_cb;

 	for (alt = region->begin; alt < region->end; alt++) {
 		int nr_inst;

 		/* Use ARM64_CB_PATCH as an unconditional patch */
 		if (alt->cpufeature < ARM64_CB_PATCH &&
 		    !cpus_have_cap(alt->cpufeature))
 			continue;

 		if (alt->cpufeature == ARM64_CB_PATCH)
 			BUG_ON(alt->alt_len != 0);
 		else
 			BUG_ON(alt->alt_len != alt->orig_len);

 		pr_info_once("patching kernel code\n");

 		origptr = ALT_ORIG_PTR(alt);
 		updptr = is_module ? origptr : lm_alias(origptr);
 		nr_inst = alt->orig_len / AARCH64_INSN_SIZE;

 		if (alt->cpufeature < ARM64_CB_PATCH)
 			alt_cb = patch_alternative;
 		else
 			alt_cb  = ALT_REPL_PTR(alt);

 		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);
 		__flush_icache_all();
 		isb();
 	}
 }

 /*
  * 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)
 {
 	struct alt_region region = {
 		.begin	= (struct alt_instr *)__alt_instructions,
 		.end	= (struct alt_instr *)__alt_instructions_end,
 	};

 	/* We always have a CPU 0 at this point (__init) */
 	if (smp_processor_id()) {
 		while (!READ_ONCE(alternatives_applied))
 			cpu_relax();
 		isb();
 	} else {
 		BUG_ON(alternatives_applied);
 		__apply_alternatives(&region, false);
 		/* Barriers provided by the cache flushing */
 		WRITE_ONCE(alternatives_applied, 1);
 	}

 	return 0;
 }

 void __init apply_alternatives_all(void)
 {
 	/* better not try code patching on a live SMP system */
 	stop_machine(__apply_alternatives_multi_stop, NULL, cpu_online_mask);
 }

 #ifdef CONFIG_MODULES
 void apply_alternatives_module(void *start, size_t length)
 {
 	struct alt_region region = {
 		.begin	= start,
 		.end	= start + length,
 	};

 	__apply_alternatives(&region, true);
 }
 #endif
	/*
	* alternative runtime patching
	* inspired by the x86 version
	*
	* Copyright (C) 2014 ARM Ltd.
	*
	* This program is free software; you can redistribute it and/or modify
	* it under the terms of the GNU General Public License version 2 as
	* published by the Free Software Foundation.
	*
	* This program is distributed in the hope that it will be useful,
	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	* GNU General Public License for more details.
	*
	* You should have received a copy of the GNU General Public License
	* along with this program. If not, see <http://www.gnu.org/licenses/>.
	*/

	#define pr_fmt(fmt) "alternatives: " fmt

	#include <linux/init.h>
	#include <linux/cpu.h>
	#include <asm/cacheflush.h>
	#include <asm/alternative.h>
	#include <asm/cpufeature.h>
	#include <asm/insn.h>
	#include <asm/sections.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)

	int alternatives_applied;

	struct alt_region {
	struct alt_instr *begin;
	struct alt_instr *end;
	};

	/*
	* Check if the target PC is within an alternative block.
	*/
	static bool branch_insn_requires_update(struct alt_instr *alt, unsigned long pc)
	{
	unsigned long replptr;

	if (kernel_text_address(pc))
	return true;

	replptr = (unsigned long)ALT_REPL_PTR(alt);
	if (pc >= replptr && pc <= (replptr + alt->alt_len))
	return false;

	/*
	* Branching into another alternate sequence is doomed, and
	* we're not even trying to fix it up.
	*/
	BUG();
	}

	#define align_down(x, a) ((unsigned long)(x) & ~(((unsigned long)(a)) - 1))

	static 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 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_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(void *alt_region, bool is_module)
	{
	struct alt_instr *alt;
	struct alt_region *region = alt_region;
	__le32 origptr, updptr;
	alternative_cb_t alt_cb;

	for (alt = region->begin; alt < region->end; alt++) {
	int nr_inst;

	/* Use ARM64_CB_PATCH as an unconditional patch */
	if (alt->cpufeature < ARM64_CB_PATCH &&
	!cpus_have_cap(alt->cpufeature))
	continue;

	if (alt->cpufeature == ARM64_CB_PATCH)
	BUG_ON(alt->alt_len != 0);
	else
	BUG_ON(alt->alt_len != alt->orig_len);

	pr_info_once("patching kernel code\n");

	origptr = ALT_ORIG_PTR(alt);
	updptr = is_module ? origptr : lm_alias(origptr);
	nr_inst = alt->orig_len / AARCH64_INSN_SIZE;

	if (alt->cpufeature < ARM64_CB_PATCH)
	alt_cb = patch_alternative;
	else
	alt_cb = ALT_REPL_PTR(alt);

	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);
	__flush_icache_all();
	isb();
	}
	}

	/*
	* 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)
	{
	struct alt_region region = {
	.begin = (struct alt_instr *)__alt_instructions,
	.end = (struct alt_instr *)__alt_instructions_end,
	};

	/* We always have a CPU 0 at this point (__init) */
	if (smp_processor_id()) {
	while (!READ_ONCE(alternatives_applied))
	cpu_relax();
	isb();
	} else {
	BUG_ON(alternatives_applied);
	__apply_alternatives(&region, false);
	/* Barriers provided by the cache flushing */
	WRITE_ONCE(alternatives_applied, 1);
	}

	return 0;
	}

	void __init apply_alternatives_all(void)
	{
	/* better not try code patching on a live SMP system */
	stop_machine(__apply_alternatives_multi_stop, NULL, cpu_online_mask);
	}

	#ifdef CONFIG_MODULES
	void apply_alternatives_module(void *start, size_t length)
	{
	struct alt_region region = {
	.begin = start,
	.end = start + length,
	};

	__apply_alternatives(&region, true);
	}
	#endif