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Diffstat (limited to '')
| -rw-r--r-- | arch/arm64/kernel/alternative.c | 228 |
1 files changed, 228 insertions, 0 deletions
diff --git a/arch/arm64/kernel/alternative.c b/arch/arm64/kernel/alternative.c new file mode 100644 index 000000000..3747c8d87 --- /dev/null +++ b/arch/arm64/kernel/alternative.c @@ -0,0 +1,228 @@ +/* + * 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 __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_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(®ion, 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(®ion, true); +} +#endif |