b9a95e85bb
This reverts most of commit fef7f2b201.
It turns out that there are a couple of problems with the way we're
fixing up branch instructions used as part of alternative instruction
sequences:
(1) If the branch target is also in the alternative sequence, we'll
generate a branch into the .altinstructions section which actually
gets freed.
(2) The calls to aarch64_insn_{read,write} bring an awful lot more
code into the patching path (e.g. taking locks, poking the fixmap,
invalidating the TLB) which isn't actually needed for the early
patching run under stop_machine, but makes the use of alternative
sequences extremely fragile (as we can't patch code that could be
used by the patching code).
Given that no code actually requires alternative patching of immediate
branches, let's remove this support for now and revisit it when we've
got a user. We leave the updated size check, since we really do require
the sequences to be the same length.
Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
86 lines
2.1 KiB
C
86 lines
2.1 KiB
C
/*
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* alternative runtime patching
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* inspired by the x86 version
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*
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* Copyright (C) 2014 ARM Ltd.
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License version 2 as
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* published by the Free Software Foundation.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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#define pr_fmt(fmt) "alternatives: " fmt
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#include <linux/init.h>
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#include <linux/cpu.h>
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#include <asm/cacheflush.h>
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#include <asm/alternative.h>
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#include <asm/cpufeature.h>
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#include <linux/stop_machine.h>
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extern struct alt_instr __alt_instructions[], __alt_instructions_end[];
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struct alt_region {
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struct alt_instr *begin;
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struct alt_instr *end;
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};
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static int __apply_alternatives(void *alt_region)
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{
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struct alt_instr *alt;
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struct alt_region *region = alt_region;
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u8 *origptr, *replptr;
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for (alt = region->begin; alt < region->end; alt++) {
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if (!cpus_have_cap(alt->cpufeature))
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continue;
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BUG_ON(alt->alt_len != alt->orig_len);
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pr_info_once("patching kernel code\n");
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origptr = (u8 *)&alt->orig_offset + alt->orig_offset;
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replptr = (u8 *)&alt->alt_offset + alt->alt_offset;
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memcpy(origptr, replptr, alt->alt_len);
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flush_icache_range((uintptr_t)origptr,
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(uintptr_t)(origptr + alt->alt_len));
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}
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return 0;
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}
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void apply_alternatives_all(void)
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{
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struct alt_region region = {
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.begin = __alt_instructions,
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.end = __alt_instructions_end,
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};
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/* better not try code patching on a live SMP system */
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stop_machine(__apply_alternatives, ®ion, NULL);
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}
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void apply_alternatives(void *start, size_t length)
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{
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struct alt_region region = {
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.begin = start,
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.end = start + length,
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};
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__apply_alternatives(®ion);
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}
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void free_alternatives_memory(void)
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{
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free_reserved_area(__alt_instructions, __alt_instructions_end,
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0, "alternatives");
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}
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