Re: [PATCH ftrace/core v6 2/5] ftrace, kprobes: Support IPMODIFY flag to find IP modify conflict

[Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>]

(2014/11/22 3:05), Steven Rostedt wrote:
> On Fri, 21 Nov 2014 05:25:16 -0500
> Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com> wrote:
> 
>>  Documentation/trace/ftrace.txt |    5 +
>>  include/linux/ftrace.h         |   16 ++++-
>>  kernel/trace/ftrace.c          |  142 +++++++++++++++++++++++++++++++++++++++-
>>  3 files changed, 159 insertions(+), 4 deletions(-)
>>
>> diff --git a/Documentation/trace/ftrace.txt b/Documentation/trace/ftrace.txt
>> index 4da4261..f10f5f5 100644
>> --- a/Documentation/trace/ftrace.txt
>> +++ b/Documentation/trace/ftrace.txt
>> @@ -234,6 +234,11 @@ of ftrace. Here is a list of some of the key files:
>>  	will be displayed on the same line as the function that
>>  	is returning registers.
>>  
>> +	If the callback registered to be traced by a function with
>> +	the "ip modify" attribute (thus the regs->ip can be changed),
>> +	an 'I' will be displayed on the same line as the function that
>> +	can be overridden.
>> +
>>    function_profile_enabled:
>>  
>>  	When set it will enable all functions with either the function
>> diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
>> index 7b2616f..93cf047 100644
>> --- a/include/linux/ftrace.h
>> +++ b/include/linux/ftrace.h
>> @@ -61,6 +61,11 @@ ftrace_func_t ftrace_ops_get_func(struct ftrace_ops *ops);
>>  /*
>>   * FTRACE_OPS_FL_* bits denote the state of ftrace_ops struct and are
>>   * set in the flags member.
>> + * CONTROL, SAVE_REGS, SAVE_REGS_IF_SUPPORTED, RECURSION_SAFE, STUB and
>> + * IPMODIFY are a kind of attribute flags which can be set only before
>> + * registering the ftrace_ops, and can not be modified while registered.
>> + * Changing those attribute flags after regsitering ftrace_ops will
>> + * cause unexpected results.
>>   *
>>   * ENABLED - set/unset when ftrace_ops is registered/unregistered
>>   * DYNAMIC - set when ftrace_ops is registered to denote dynamically
>> @@ -101,6 +106,10 @@ ftrace_func_t ftrace_ops_get_func(struct ftrace_ops *ops);
>>   *            The ftrace_ops trampoline can be set by the ftrace users, and
>>   *            in such cases the arch must not modify it. Only the arch ftrace
>>   *            core code should set this flag.
>> + * IPMODIFY - The ops can modify the IP register. This can only be set with
>> + *            SAVE_REGS. If another ops is already registered for any of the
>> + *            functions that this ops will be registered for, then this ops
>> + *            will fail to register or set_filter_ip.
> 
> It's blocked by any ops sharing the same function, or just another ops
> with this flag set? The comment doesn't specify. The code looks like
> the latter.

Ah, right! IPMODIFY blocks another IPMODIFY-ed ops. So the comment should
be fixed.

> 
> 
>>   */
>>  enum {
>>  	FTRACE_OPS_FL_ENABLED			= 1 << 0,
>> @@ -116,6 +125,7 @@ enum {
>>  	FTRACE_OPS_FL_REMOVING			= 1 << 10,
>>  	FTRACE_OPS_FL_MODIFYING			= 1 << 11,
>>  	FTRACE_OPS_FL_ALLOC_TRAMP		= 1 << 12,
>> +	FTRACE_OPS_FL_IPMODIFY			= 1 << 13,
>>  };
>>  
>>  #ifdef CONFIG_DYNAMIC_FTRACE
>> @@ -310,6 +320,7 @@ bool is_ftrace_trampoline(unsigned long addr);
>>   *  ENABLED - the function is being traced
>>   *  REGS    - the record wants the function to save regs
>>   *  REGS_EN - the function is set up to save regs.
>> + *  IPMODIFY - the record allows for the IP address to be changed.
>>   *
>>   * When a new ftrace_ops is registered and wants a function to save
>>   * pt_regs, the rec->flag REGS is set. When the function has been
>> @@ -323,10 +334,11 @@ enum {
>>  	FTRACE_FL_REGS_EN	= (1UL << 29),
>>  	FTRACE_FL_TRAMP		= (1UL << 28),
>>  	FTRACE_FL_TRAMP_EN	= (1UL << 27),
>> +	FTRACE_FL_IPMODIFY	= (1UL << 26),
>>  };
>>  
>> -#define FTRACE_REF_MAX_SHIFT	27
>> -#define FTRACE_FL_BITS		5
>> +#define FTRACE_REF_MAX_SHIFT	26
>> +#define FTRACE_FL_BITS		6
>>  #define FTRACE_FL_MASKED_BITS	((1UL << FTRACE_FL_BITS) - 1)
>>  #define FTRACE_FL_MASK		(FTRACE_FL_MASKED_BITS << FTRACE_REF_MAX_SHIFT)
>>  #define FTRACE_REF_MAX		((1UL << FTRACE_REF_MAX_SHIFT) - 1)
>> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
>> index fa0f36b..baa2c4d 100644
>> --- a/kernel/trace/ftrace.c
>> +++ b/kernel/trace/ftrace.c
>> @@ -1358,6 +1358,9 @@ ftrace_hash_rec_disable_modify(struct ftrace_ops *ops, int filter_hash);
>>  static void
>>  ftrace_hash_rec_enable_modify(struct ftrace_ops *ops, int filter_hash);
>>  
>> +static int ftrace_hash_ipmodify_update(struct ftrace_ops *ops,
>> +				       struct ftrace_hash *new_hash);
>> +
>>  static int
>>  ftrace_hash_move(struct ftrace_ops *ops, int enable,
>>  		 struct ftrace_hash **dst, struct ftrace_hash *src)
>> @@ -1368,8 +1371,13 @@ ftrace_hash_move(struct ftrace_ops *ops, int enable,
>>  	struct ftrace_hash *new_hash;
>>  	int size = src->count;
>>  	int bits = 0;
>> +	int ret;
>>  	int i;
>>  
>> +	/* Reject setting notrace hash on IPMODIFY ftrace_ops */
>> +	if (ops->flags & FTRACE_OPS_FL_IPMODIFY && !enable)
>> +		return -EINVAL;
>> +
>>  	/*
>>  	 * If the new source is empty, just free dst and assign it
>>  	 * the empty_hash.
>> @@ -1403,6 +1411,16 @@ ftrace_hash_move(struct ftrace_ops *ops, int enable,
>>  	}
>>  
>>  update:
>> +	/* Make sure this can be applied if it is IPMODIFY ftrace_ops */
>> +	if (enable) {
>> +		/* IPMODIFY should be updated only when filter_hash updating */
>> +		ret = ftrace_hash_ipmodify_update(ops, new_hash);
>> +		if (ret < 0) {
>> +			free_ftrace_hash(new_hash);
>> +			return ret;
>> +		}
>> +	}
>> +
>>  	/*
>>  	 * Remove the current set, update the hash and add
>>  	 * them back.
>> @@ -1767,6 +1785,114 @@ static void ftrace_hash_rec_enable_modify(struct ftrace_ops *ops,
>>  	ftrace_hash_rec_update_modify(ops, filter_hash, 1);
>>  }
>>  
>> +/*
>> + * Try to update IPMODIFY flag on each ftrace_rec. Return 0 if it is OK
>> + * or no-needed to update, -EBUSY if it detects a conflict of the flag
>> + * on a ftrace_rec, and -EINVAL if the new_hash tries to trace all recs.
>> + * Note that old_hash and new_hash has below meanings
>> + *  - If the hash is NULL, it hits all recs (if IPMODIFY is set, this is rejected)
>> + *  - If the hash is EMPTY_HASH, it hits nothing
>> + *  - Anything else hits the recs which match the hash entries.
>> + */
>> +static int __ftrace_hash_update_ipmodify(struct ftrace_ops *ops,
>> +					 struct ftrace_hash *old_hash,
>> +					 struct ftrace_hash *new_hash)
>> +{
>> +	struct ftrace_page *pg;
>> +	struct dyn_ftrace *rec, *end = NULL;
>> +	int in_old, in_new;
>> +
>> +	/* Only update if the ops has been registered */
>> +	if (!(ops->flags & FTRACE_OPS_FL_ENABLED))
>> +		return 0;
>> +
>> +	if (!(ops->flags & FTRACE_OPS_FL_IPMODIFY))
>> +		return 0;
>> +
>> +	/*
>> +	 * Since the IPMODIFY is very address sensitive action, we do not allow
> 
>  is *a* very address sensitive action

Right.

> 
> The rest looks good.

Thanks!

> 
> -- Steve
> 
>> +	 * ftrace_ops to set all functions to new hash.
>> +	 */
>> +	if (!new_hash || !old_hash)
>> +		return -EINVAL;
>> +
>> +	/* Update rec->flags */
>> +	do_for_each_ftrace_rec(pg, rec) {
>> +		/* We need to update only differences of filter_hash */
>> +		in_old = !!ftrace_lookup_ip(old_hash, rec->ip);
>> +		in_new = !!ftrace_lookup_ip(new_hash, rec->ip);
>> +		if (in_old == in_new)
>> +			continue;
>> +
>> +		if (in_new) {
>> +			/* New entries must ensure no others are using it */
>> +			if (rec->flags & FTRACE_FL_IPMODIFY)
>> +				goto rollback;
>> +			rec->flags |= FTRACE_FL_IPMODIFY;
>> +		} else /* Removed entry */
>> +			rec->flags &= ~FTRACE_FL_IPMODIFY;
>> +	} while_for_each_ftrace_rec();
>> +
>> +	return 0;
>> +
>> +rollback:
>> +	end = rec;
>> +
>> +	/* Roll back what we did above */
>> +	do_for_each_ftrace_rec(pg, rec) {
>> +		if (rec == end)
>> +			goto err_out;
>> +
>> +		in_old = !!ftrace_lookup_ip(old_hash, rec->ip);
>> +		in_new = !!ftrace_lookup_ip(new_hash, rec->ip);
>> +		if (in_old == in_new)
>> +			continue;
>> +
>> +		if (in_new)
>> +			rec->flags &= ~FTRACE_FL_IPMODIFY;
>> +		else
>> +			rec->flags |= FTRACE_FL_IPMODIFY;
>> +	} while_for_each_ftrace_rec();
>> +
>> +err_out:
>> +	return -EBUSY;
>> +}
>> +
>> +static int ftrace_hash_ipmodify_enable(struct ftrace_ops *ops)
>> +{
>> +	struct ftrace_hash *hash = ops->func_hash->filter_hash;
>> +
>> +	if (ftrace_hash_empty(hash))
>> +		hash = NULL;
>> +
>> +	return __ftrace_hash_update_ipmodify(ops, EMPTY_HASH, hash);
>> +}
>> +
>> +/* Disabling always succeeds */
>> +static void ftrace_hash_ipmodify_disable(struct ftrace_ops *ops)
>> +{
>> +	struct ftrace_hash *hash = ops->func_hash->filter_hash;
>> +
>> +	if (ftrace_hash_empty(hash))
>> +		hash = NULL;
>> +
>> +	__ftrace_hash_update_ipmodify(ops, hash, EMPTY_HASH);
>> +}
>> +
>> +static int ftrace_hash_ipmodify_update(struct ftrace_ops *ops,
>> +				       struct ftrace_hash *new_hash)
>> +{
>> +	struct ftrace_hash *old_hash = ops->func_hash->filter_hash;
>> +
>> +	if (ftrace_hash_empty(old_hash))
>> +		old_hash = NULL;
>> +
>> +	if (ftrace_hash_empty(new_hash))
>> +		new_hash = NULL;
>> +
>> +	return __ftrace_hash_update_ipmodify(ops, old_hash, new_hash);
>> +}
>> +
>>  static void print_ip_ins(const char *fmt, unsigned char *p)
>>  {
>>  	int i;
>> @@ -2436,6 +2562,15 @@ static int ftrace_startup(struct ftrace_ops *ops, int command)
>>  	 */
>>  	ops->flags |= FTRACE_OPS_FL_ENABLED | FTRACE_OPS_FL_ADDING;
>>  
>> +	ret = ftrace_hash_ipmodify_enable(ops);
>> +	if (ret < 0) {
>> +		/* Rollback registration process */
>> +		__unregister_ftrace_function(ops);
>> +		ftrace_start_up--;
>> +		ops->flags &= ~FTRACE_OPS_FL_ENABLED;
>> +		return ret;
>> +	}
>> +
>>  	ftrace_hash_rec_enable(ops, 1);
>>  
>>  	ftrace_startup_enable(command);
>> @@ -2464,6 +2599,8 @@ static int ftrace_shutdown(struct ftrace_ops *ops, int command)
>>  	 */
>>  	WARN_ON_ONCE(ftrace_start_up < 0);
>>  
>> +	/* Disabling ipmodify never fails */
>> +	ftrace_hash_ipmodify_disable(ops);
>>  	ftrace_hash_rec_disable(ops, 1);
>>  
>>  	ops->flags &= ~FTRACE_OPS_FL_ENABLED;
>> @@ -3058,9 +3195,10 @@ static int t_show(struct seq_file *m, void *v)
>>  	if (iter->flags & FTRACE_ITER_ENABLED) {
>>  		struct ftrace_ops *ops = NULL;
>>  
>> -		seq_printf(m, " (%ld)%s",
>> +		seq_printf(m, " (%ld)%s%s",
>>  			   ftrace_rec_count(rec),
>> -			   rec->flags & FTRACE_FL_REGS ? " R" : "  ");
>> +			   rec->flags & FTRACE_FL_REGS ? " R" : "  ",
>> +			   rec->flags & FTRACE_FL_IPMODIFY ? " I" : "  ");
>>  		if (rec->flags & FTRACE_FL_TRAMP_EN) {
>>  			ops = ftrace_find_tramp_ops_any(rec);
>>  			if (ops)
>>
> 
> 


-- 
Masami HIRAMATSU
Software Platform Research Dept. Linux Technology Research Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@hitachi.com