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

From: Masami Hiramatsu
Date: Sun Nov 23 2014 - 21:07:11 EST

(2014/11/22 3:05), Steven Rostedt wrote:
> On Fri, 21 Nov 2014 05:25:16 -0500
> Masami Hiramatsu <masami.hiramatsu.pt@xxxxxxxxxxx> 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@xxxxxxxxxxx


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