Re: [PATCH 2/3] x86/alternatives,jump_label: Provide better text_poke() batching interface

[Masami Hiramatsu]

Hi Peter,

On Tue, 27 Aug 2019 20:06:24 +0200
Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:

> Adding another text_poke_bp_batch() user made me realize the interface
> is all sorts of wrong. The text poke vector should be internal to the
> implementation.
> 
> This then results in a trivial interface:
> 
>   text_poke_queue()  - which has the 'normal' text_poke_bp() interface
>   text_poke_finish() - which takes no arguments and flushes any
>                        pending text_poke()s.

Looks good to me. Maybe it is easy to apply to optprobe too.

Reviewed-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>

Thank you,

> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
> Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
> Cc: Daniel Bristot de Oliveira <bristot@xxxxxxxxxx>
> Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
> ---
>  arch/x86/include/asm/text-patching.h |   16 ++-----
>  arch/x86/kernel/alternative.c        |   64 +++++++++++++++++++++++++---
>  arch/x86/kernel/jump_label.c         |   80 +++++++++--------------------------
>  3 files changed, 84 insertions(+), 76 deletions(-)
> 
> --- a/arch/x86/include/asm/text-patching.h
> +++ b/arch/x86/include/asm/text-patching.h
> @@ -25,14 +25,6 @@ static inline void apply_paravirt(struct
>   */
>  #define POKE_MAX_OPCODE_SIZE	5
>  
> -struct text_poke_loc {
> -	void *addr;
> -	int len;
> -	s32 rel32;
> -	u8 opcode;
> -	const char text[POKE_MAX_OPCODE_SIZE];
> -};
> -
>  extern void text_poke_early(void *addr, const void *opcode, size_t len);
>  
>  /*
> @@ -53,13 +45,15 @@ extern void *text_poke(void *addr, const
>  extern void *text_poke_kgdb(void *addr, const void *opcode, size_t len);
>  extern int poke_int3_handler(struct pt_regs *regs);
>  extern void text_poke_bp(void *addr, const void *opcode, size_t len, const void *emulate);
> -extern void text_poke_bp_batch(struct text_poke_loc *tp, unsigned int nr_entries);
> -extern void text_poke_loc_init(struct text_poke_loc *tp, void *addr,
> -			       const void *opcode, size_t len, const void *emulate);
> +
> +extern void text_poke_queue(void *addr, const void *opcode, size_t len, const void *emulate);
> +extern void text_poke_finish(void);
> +
>  extern int after_bootmem;
>  extern __ro_after_init struct mm_struct *poking_mm;
>  extern __ro_after_init unsigned long poking_addr;
>  
> +
>  #ifndef CONFIG_UML_X86
>  static inline void int3_emulate_jmp(struct pt_regs *regs, unsigned long ip)
>  {
> --- a/arch/x86/kernel/alternative.c
> +++ b/arch/x86/kernel/alternative.c
> @@ -936,6 +936,14 @@ static void do_sync_core(void *info)
>  	sync_core();
>  }
>  
> +struct text_poke_loc {
> +	void *addr;
> +	int len;
> +	s32 rel32;
> +	u8 opcode;
> +	const char text[POKE_MAX_OPCODE_SIZE];
> +};
> +
>  static struct bp_patching_desc {
>  	struct text_poke_loc *vec;
>  	int nr_entries;
> @@ -1017,6 +1025,10 @@ int poke_int3_handler(struct pt_regs *re
>  }
>  NOKPROBE_SYMBOL(poke_int3_handler);
>  
> +#define TP_VEC_MAX (PAGE_SIZE / sizeof(struct text_poke_loc))
> +static struct text_poke_loc tp_vec[TP_VEC_MAX];
> +static int tp_vec_nr;
> +
>  /**
>   * text_poke_bp_batch() -- update instructions on live kernel on SMP
>   * @tp:			vector of instructions to patch
> @@ -1038,7 +1050,7 @@ NOKPROBE_SYMBOL(poke_int3_handler);
>   *		  replacing opcode
>   *	- sync cores
>   */
> -void text_poke_bp_batch(struct text_poke_loc *tp, unsigned int nr_entries)
> +static void text_poke_bp_batch(struct text_poke_loc *tp, unsigned int nr_entries)
>  {
>  	unsigned char int3 = INT3_INSN_OPCODE;
>  	int patched_all_but_first = 0;
> @@ -1105,11 +1117,7 @@ void text_poke_loc_init(struct text_poke
>  {
>  	struct insn insn;
>  
> -	if (!opcode)
> -		opcode = (void *)tp->text;
> -	else
> -		memcpy((void *)tp->text, opcode, len);
> -
> +	memcpy((void *)tp->text, opcode, len);
>  	if (!emulate)
>  		emulate = opcode;
>  
> @@ -1147,6 +1155,50 @@ void text_poke_loc_init(struct text_poke
>  	}
>  }
>  
> +/*
> + * We hard rely on the tp_vec being ordered; ensure this is so by flushing
> + * early if needed.
> + */
> +static bool tp_order_fail(void *addr)
> +{
> +	struct text_poke_loc *tp;
> +
> +	if (!tp_vec_nr)
> +		return false;
> +
> +	if (!addr) /* force */
> +		return true;
> +
> +	tp = &tp_vec[tp_vec_nr - 1];
> +	if ((unsigned long)tp->addr > (unsigned long)addr)
> +		return true;
> +
> +	return false;
> +}
> +
> +static void text_poke_flush(void *addr)
> +{
> +	if (tp_vec_nr == TP_VEC_MAX || tp_order_fail(addr)) {
> +		text_poke_bp_batch(tp_vec, tp_vec_nr);
> +		tp_vec_nr = 0;
> +	}
> +}
> +
> +void text_poke_finish(void)
> +{
> +	text_poke_flush(NULL);
> +}
> +
> +void text_poke_queue(void *addr, const void *opcode, size_t len, const void *emulate)
> +{
> +	struct text_poke_loc *tp;
> +
> +	text_poke_flush(addr);
> +
> +	tp = &tp_vec[tp_vec_nr++];
> +	text_poke_loc_init(tp, addr, opcode, len, emulate);
> +}
> +
>  /**
>   * text_poke_bp() -- update instructions on live kernel on SMP
>   * @addr:	address to patch
> --- a/arch/x86/kernel/jump_label.c
> +++ b/arch/x86/kernel/jump_label.c
> @@ -35,18 +35,19 @@ static void bug_at(unsigned char *ip, in
>  	BUG();
>  }
>  
> -static void __jump_label_set_jump_code(struct jump_entry *entry,
> -				       enum jump_label_type type,
> -				       union jump_code_union *code,
> -				       int init)
> +static const void *
> +__jump_label_set_jump_code(struct jump_entry *entry, enum jump_label_type type, int init)
>  {
> +	static union jump_code_union code; /* relies on text_mutex */
>  	const unsigned char default_nop[] = { STATIC_KEY_INIT_NOP };
>  	const unsigned char *ideal_nop = ideal_nops[NOP_ATOMIC5];
>  	const void *expect;
>  	int line;
>  
> -	code->jump = 0xe9;
> -	code->offset = jump_entry_target(entry) -
> +	lockdep_assert_held(&text_mutex);
> +
> +	code.jump = JMP32_INSN_OPCODE;
> +	code.offset = jump_entry_target(entry) -
>  		       (jump_entry_code(entry) + JUMP_LABEL_NOP_SIZE);
>  
>  	if (init) {
> @@ -54,23 +55,23 @@ static void __jump_label_set_jump_code(s
>  	} else if (type == JUMP_LABEL_JMP) {
>  		expect = ideal_nop; line = __LINE__;
>  	} else {
> -		expect = code->code; line = __LINE__;
> +		expect = code.code; line = __LINE__;
>  	}
>  
>  	if (memcmp((void *)jump_entry_code(entry), expect, JUMP_LABEL_NOP_SIZE))
>  		bug_at((void *)jump_entry_code(entry), line);
>  
>  	if (type == JUMP_LABEL_NOP)
> -		memcpy(code, ideal_nop, JUMP_LABEL_NOP_SIZE);
> +		memcpy(&code, ideal_nop, JUMP_LABEL_NOP_SIZE);
> +
> +	return &code;
>  }
>  
>  static void __ref __jump_label_transform(struct jump_entry *entry,
>  					 enum jump_label_type type,
>  					 int init)
>  {
> -	union jump_code_union code;
> -
> -	__jump_label_set_jump_code(entry, type, &code, init);
> +	const void *opcode = __jump_label_set_jump_code(entry, type, init);
>  
>  	/*
>  	 * As long as only a single processor is running and the code is still
> @@ -84,12 +85,12 @@ static void __ref __jump_label_transform
>  	 * always nop being the 'currently valid' instruction
>  	 */
>  	if (init || system_state == SYSTEM_BOOTING) {
> -		text_poke_early((void *)jump_entry_code(entry), &code,
> +		text_poke_early((void *)jump_entry_code(entry), opcode,
>  				JUMP_LABEL_NOP_SIZE);
>  		return;
>  	}
>  
> -	text_poke_bp((void *)jump_entry_code(entry), &code, JUMP_LABEL_NOP_SIZE, NULL);
> +	text_poke_bp((void *)jump_entry_code(entry), opcode, JUMP_LABEL_NOP_SIZE, NULL);
>  }
>  
>  void arch_jump_label_transform(struct jump_entry *entry,
> @@ -100,15 +101,10 @@ void arch_jump_label_transform(struct ju
>  	mutex_unlock(&text_mutex);
>  }
>  
> -#define TP_VEC_MAX (PAGE_SIZE / sizeof(struct text_poke_loc))
> -static struct text_poke_loc tp_vec[TP_VEC_MAX];
> -static int tp_vec_nr;
> -
>  bool arch_jump_label_transform_queue(struct jump_entry *entry,
>  				     enum jump_label_type type)
>  {
> -	struct text_poke_loc *tp;
> -	void *entry_code;
> +	const void *opcode;
>  
>  	if (system_state == SYSTEM_BOOTING) {
>  		/*
> @@ -118,53 +114,19 @@ bool arch_jump_label_transform_queue(str
>  		return true;
>  	}
>  
> -	/*
> -	 * No more space in the vector, tell upper layer to apply
> -	 * the queue before continuing.
> -	 */
> -	if (tp_vec_nr == TP_VEC_MAX)
> -		return false;
> -
> -	tp = &tp_vec[tp_vec_nr];
> -
> -	entry_code = (void *)jump_entry_code(entry);
> -
> -	/*
> -	 * The INT3 handler will do a bsearch in the queue, so we need entries
> -	 * to be sorted. We can survive an unsorted list by rejecting the entry,
> -	 * forcing the generic jump_label code to apply the queue. Warning once,
> -	 * to raise the attention to the case of an unsorted entry that is
> -	 * better not happen, because, in the worst case we will perform in the
> -	 * same way as we do without batching - with some more overhead.
> -	 */
> -	if (tp_vec_nr > 0) {
> -		int prev = tp_vec_nr - 1;
> -		struct text_poke_loc *prev_tp = &tp_vec[prev];
> -
> -		if (WARN_ON_ONCE(prev_tp->addr > entry_code))
> -			return false;
> -	}
> -
> -	__jump_label_set_jump_code(entry, type,
> -				   (union jump_code_union *)&tp->text, 0);
> -
> -	text_poke_loc_init(tp, entry_code, NULL, JUMP_LABEL_NOP_SIZE, NULL);
> -
> -	tp_vec_nr++;
> -
> +	mutex_lock(&text_mutex);
> +	opcode = __jump_label_set_jump_code(entry, type, 0);
> +	text_poke_queue((void *)jump_entry_code(entry),
> +			opcode, JUMP_LABEL_NOP_SIZE, NULL);
> +	mutex_unlock(&text_mutex);
>  	return true;
>  }
>  
>  void arch_jump_label_transform_apply(void)
>  {
> -	if (!tp_vec_nr)
> -		return;
> -
>  	mutex_lock(&text_mutex);
> -	text_poke_bp_batch(tp_vec, tp_vec_nr);
> +	text_poke_finish();
>  	mutex_unlock(&text_mutex);
> -
> -	tp_vec_nr = 0;
>  }
>  
>  static enum {
> 
> 


-- 
Masami Hiramatsu <mhiramat@xxxxxxxxxx>