cregit-Linux how code gets into the kernel

Release 4.17 arch/arm64/kernel/alternative.c

Directory: arch/arm64/kernel
/*
 * 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 1;

	replptr = (unsigned long)ALT_REPL_PTR(alt);
	if (pc >= replptr && pc <= (replptr + alt->alt_len))
		return 0;

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


Contributors
PersonTokensPropCommitsCommitProp
Marc Zyngier63100.00%1100.00%


Total63100.00%1100.00%




#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;
}


Contributors
PersonTokensPropCommitsCommitProp
Marc Zyngier9355.69%125.00%


Suzuki K. Poulose7243.11%250.00%


Luc Van Oostenryck21.20%125.00%


Total167100.00%4100.00%






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);
	}
}


Contributors
PersonTokensPropCommitsCommitProp
Marc Zyngier79100.00%1100.00%


Total79100.00%1100.00%






static void __apply_alternatives(void *alt_region, bool use_linear_alias)
{
	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 = use_linear_alias ? lm_alias(origptr) : 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);

		flush_icache_range((uintptr_t)origptr,
				   (uintptr_t)(origptr + nr_inst));
	}
}


Contributors
PersonTokensPropCommitsCommitProp
Andre Przywara9753.01%225.00%


Marc Zyngier6837.16%337.50%


Ard Biesheuvel168.74%112.50%


Luc Van Oostenryck10.55%112.50%


Will Deacon10.55%112.50%


Total183100.00%8100.00%



/*
 * 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, true);
		/* Barriers provided by the cache flushing */
		WRITE_ONCE(alternatives_applied, 1);
	}

	return 0;
}


Contributors
PersonTokensPropCommitsCommitProp
Will Deacon4654.12%228.57%


Andre Przywara2428.24%228.57%


James Morse1315.29%228.57%


Ard Biesheuvel22.35%114.29%


Total85100.00%7100.00%






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);
}


Contributors
PersonTokensPropCommitsCommitProp
Will Deacon1372.22%150.00%


Andre Przywara527.78%150.00%


Total18100.00%2100.00%






void apply_alternatives(void *start, size_t length)
{
	struct alt_region region = {
		.begin	= start,
		.end	= start + length,
        };

	__apply_alternatives(&region, false);
}

Contributors
PersonTokensPropCommitsCommitProp
Andre Przywara3694.74%150.00%


Ard Biesheuvel25.26%150.00%


Total38100.00%2100.00%




Overall Contributors
PersonTokensPropCommitsCommitProp
Marc Zyngier32945.89%323.08%


Andre Przywara20328.31%215.38%


Suzuki K. Poulose8111.30%215.38%


Will Deacon618.51%215.38%


Ard Biesheuvel202.79%17.69%


James Morse192.65%215.38%


Luc Van Oostenryck40.56%17.69%


Total717100.00%13100.00%


Directory: arch/arm64/kernel



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