diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c index 30e86730655cc..34360ca301a2e 100644 --- a/arch/x86/kernel/alternative.c +++ b/arch/x86/kernel/alternative.c @@ -948,10 +948,29 @@ struct text_poke_loc { const u8 text[POKE_MAX_OPCODE_SIZE]; }; -static struct bp_patching_desc { +struct bp_patching_desc { struct text_poke_loc *vec; int nr_entries; -} bp_patching; + atomic_t refs; +}; + +static struct bp_patching_desc *bp_desc; + +static inline struct bp_patching_desc *try_get_desc(struct bp_patching_desc **descp) +{ + struct bp_patching_desc *desc = READ_ONCE(*descp); /* rcu_dereference */ + + if (!desc || !atomic_inc_not_zero(&desc->refs)) + return NULL; + + return desc; +} + +static inline void put_desc(struct bp_patching_desc *desc) +{ + smp_mb__before_atomic(); + atomic_dec(&desc->refs); +} static inline void *text_poke_addr(struct text_poke_loc *tp) { @@ -972,26 +991,26 @@ NOKPROBE_SYMBOL(patch_cmp); int notrace poke_int3_handler(struct pt_regs *regs) { + struct bp_patching_desc *desc; struct text_poke_loc *tp; + int len, ret = 0; void *ip; - int len; + + if (user_mode(regs)) + return 0; /* * Having observed our INT3 instruction, we now must observe - * bp_patching.nr_entries. + * bp_desc: * - * nr_entries != 0 INT3 + * bp_desc = desc INT3 * WMB RMB - * write INT3 if (nr_entries) - * - * Idem for other elements in bp_patching. + * write INT3 if (desc) */ smp_rmb(); - if (likely(!bp_patching.nr_entries)) - return 0; - - if (user_mode(regs)) + desc = try_get_desc(&bp_desc); + if (!desc) return 0; /* @@ -1002,16 +1021,16 @@ int notrace poke_int3_handler(struct pt_regs *regs) /* * Skip the binary search if there is a single member in the vector. */ - if (unlikely(bp_patching.nr_entries > 1)) { - tp = bsearch(ip, bp_patching.vec, bp_patching.nr_entries, + if (unlikely(desc->nr_entries > 1)) { + tp = bsearch(ip, desc->vec, desc->nr_entries, sizeof(struct text_poke_loc), patch_cmp); if (!tp) - return 0; + goto out_put; } else { - tp = bp_patching.vec; + tp = desc->vec; if (text_poke_addr(tp) != ip) - return 0; + goto out_put; } len = text_opcode_size(tp->opcode); @@ -1023,7 +1042,7 @@ int notrace poke_int3_handler(struct pt_regs *regs) * Someone poked an explicit INT3, they'll want to handle it, * do not consume. */ - return 0; + goto out_put; case CALL_INSN_OPCODE: int3_emulate_call(regs, (long)ip + tp->rel32); @@ -1038,7 +1057,11 @@ int notrace poke_int3_handler(struct pt_regs *regs) BUG(); } - return 1; + ret = 1; + +out_put: + put_desc(desc); + return ret; } NOKPROBE_SYMBOL(poke_int3_handler); @@ -1069,14 +1092,18 @@ static int tp_vec_nr; */ static void text_poke_bp_batch(struct text_poke_loc *tp, unsigned int nr_entries) { + struct bp_patching_desc desc = { + .vec = tp, + .nr_entries = nr_entries, + .refs = ATOMIC_INIT(1), + }; unsigned char int3 = INT3_INSN_OPCODE; unsigned int i; int do_sync; lockdep_assert_held(&text_mutex); - bp_patching.vec = tp; - bp_patching.nr_entries = nr_entries; + smp_store_release(&bp_desc, &desc); /* rcu_assign_pointer */ /* * Corresponding read barrier in int3 notifier for making sure the @@ -1131,17 +1158,12 @@ static void text_poke_bp_batch(struct text_poke_loc *tp, unsigned int nr_entries text_poke_sync(); /* - * sync_core() implies an smp_mb() and orders this store against - * the writing of the new instruction. + * Remove and synchronize_rcu(), except we have a very primitive + * refcount based completion. */ - bp_patching.nr_entries = 0; - /* - * This sync_core () call ensures that all INT3 handlers in progress - * have finished. This allows poke_int3_handler() after this to - * avoid touching bp_paching.vec by checking nr_entries == 0. - */ - text_poke_sync(); - bp_patching.vec = NULL; + WRITE_ONCE(bp_desc, NULL); /* RCU_INIT_POINTER */ + if (!atomic_dec_and_test(&desc.refs)) + atomic_cond_read_acquire(&desc.refs, !VAL); } void text_poke_loc_init(struct text_poke_loc *tp, void *addr,