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/*
* 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();
}
#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);
}
}
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));
}
}
/*
* 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(®ion, true);
/* 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);
}
void apply_alternatives(void *start, size_t length)
{
struct alt_region region = {
.begin = start,
.end = start + length,
};
__apply_alternatives(®ion, false);
}
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