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Message-ID: <0d9f644f-3d60-02c3-7ce0-01296757e181@akamai.com>
Date: Mon, 12 Sep 2022 16:17:00 -0400
From: Jason Baron <jbaron@...mai.com>
To: jim.cromie@...il.com
Cc: Greg KH <gregkh@...uxfoundation.org>,
dri-devel <dri-devel@...ts.freedesktop.org>,
amd-gfx mailing list <amd-gfx@...ts.freedesktop.org>,
intel-gvt-dev@...ts.freedesktop.org,
Intel Graphics Development <intel-gfx@...ts.freedesktop.org>,
LKML <linux-kernel@...r.kernel.org>,
Daniel Vetter <daniel.vetter@...ll.ch>,
Sean Paul <seanpaul@...omium.org>, robdclark@...il.com,
Rasmus Villemoes <linux@...musvillemoes.dk>,
Joe Perches <joe@...ches.com>
Subject: Re: [PATCH v6 17/57] dyndbg: validate class FOO by checking with
module
On 9/9/22 16:44, jim.cromie@...il.com wrote:
> On Wed, Sep 7, 2022 at 12:19 PM Jason Baron <jbaron@...mai.com> wrote:
>>
>>
>>
>> On 9/4/22 17:40, Jim Cromie wrote:
>>> Add module-to-class validation:
>>>
>>> #> echo class DRM_UT_KMS +p > /proc/dynamic_debug/control
>>>
>>> If a query has "class FOO", then ddebug_find_valid_class(), called
>>> from ddebug_change(), requires that FOO is known to module X,
>>> otherwize the query is skipped entirely for X. This protects each
>>> module's class-space, other than the default:31.
>>>
>>> The authors' choice of FOO is highly selective, giving isolation
>>> and/or coordinated sharing of FOOs. For example, only DRM modules
>>> should know and respond to DRM_UT_KMS.
>>>
>>> So this, combined with module's opt-in declaration of known classes,
>>> effectively privatizes the .class_id space for each module (or
>>> coordinated set of modules).
>>>
>>> Notes:
>>>
>>> For all "class FOO" queries, ddebug_find_valid_class() is called, it
>>> returns the map matching the query, and sets valid_class via an
>>> *outvar).
>>>
>>> If no "class FOO" is supplied, valid_class = _CLASS_DFLT. This
>>> insures that legacy queries do not trample on new class'd callsites,
>>> as they get added.
>>
>>
>> Hi Jim,
>>
>> I'm wondering about the case where we have a callsite which is marked
>> as 'class foo', but the query string is done by say module and file, so:
>>
>> # echo "module bar file foo.c +p" > /proc/dynamic_debug_control
>>
>> With the proposed code, I think this ends up not enabling anything right?
>
> correct - the only way to enable : pr_debug_cls(CL_FOO, " ...")
> is
> echo class CL_FOO +p > control
>
> 1st, existing dyndbg query uses, whether ad-hoc or scripted,
> were not written in anticipation of new / classified subsystems.
>
> 2nd, new class users dont want to sit in coach. no damn legroom.
>
> 3rd, consider DRM, which already has drm.debug
> ie: /sys/module/drm/parameters/debug
> and prefers it, at least by inertia.
> protecting these new class'd callsites (3-5k of them)
> from casual (unintended) manipulations of the kernel-wide
> dyndbg state seems prudent, and a usability win.
>
> Not everyone will use module bar, requiring "class foo"
> guarantees that changes are intentional.
>
I sort of get that your trying to protect these from unintended toggling,
but I would say it's that's not really new with these statements,
prr_debug() come and go before and I'm not aware of this is an issue.
And in any case, a query can be modified.
I think what bugs me is now query stuff works differently. Previously,
all the query strings - 'module', 'file', 'line', 'format', were
used as additional selectors, but now we have this new one 'class'
that works differently as it's requited for pr_debug_cls() statements.
>
>
>> Because valid class is set to _DPRINTK_CLASS_DFLT and then:
>> 'dp->class_id != valid_class' is true?
>>
>> This seems confusing to me as a user as this doesn't work like the
>> other queries....so maybe we should only do the
>> 'dp->class_id != valid_class' check *if* query->class_string is set,
>> see below.
>>
>
> Could you clarify whether you think this is a logic error
> or a frame-of-reference difference as elaborated above ?
'frame-of-reference' I'm questioning the how 'class' works as mentioned
above not the implementation.
Thanks,
-Jason
>
> ISTM theres a place for a well-worded paragraph in doc
> about the class distinction, perhaps a whole for-authors section.
>
>
>
>>
>>
>>>
>>> Also add a new column to control-file output, displaying non-default
>>> class-name (when found) or the "unknown _id:", if it has not been
>>> (correctly) declared with one of the declarator macros.
>>>
>>> Signed-off-by: Jim Cromie <jim.cromie@...il.com>
>>> ---
>>> lib/dynamic_debug.c | 76 ++++++++++++++++++++++++++++++++++++++++-----
>>> 1 file changed, 68 insertions(+), 8 deletions(-)
>>>
>>> diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c
>>> index b71efd0b491d..db96ded78c3f 100644
>>> --- a/lib/dynamic_debug.c
>>> +++ b/lib/dynamic_debug.c
>>> @@ -56,6 +56,7 @@ struct ddebug_query {
>>> const char *module;
>>> const char *function;
>>> const char *format;
>>> + const char *class_string;
>>> unsigned int first_lineno, last_lineno;
>>> };
>>>
>>> @@ -136,15 +137,33 @@ static void vpr_info_dq(const struct ddebug_query *query, const char *msg)
>>> fmtlen--;
>>> }
>>>
>>> - v3pr_info("%s: func=\"%s\" file=\"%s\" module=\"%s\" format=\"%.*s\" lineno=%u-%u\n",
>>> - msg,
>>> - query->function ?: "",
>>> - query->filename ?: "",
>>> - query->module ?: "",
>>> - fmtlen, query->format ?: "",
>>> - query->first_lineno, query->last_lineno);
>>> + v3pr_info("%s: func=\"%s\" file=\"%s\" module=\"%s\" format=\"%.*s\" lineno=%u-%u class=%s\n",
>>> + msg,
>>> + query->function ?: "",
>>> + query->filename ?: "",
>>> + query->module ?: "",
>>> + fmtlen, query->format ?: "",
>>> + query->first_lineno, query->last_lineno, query->class_string);
>>> }
>>>
>>> +static struct ddebug_class_map *ddebug_find_valid_class(struct ddebug_table const *dt,
>>> + const char *class_string, int *class_id)
>>> +{
>>> + struct ddebug_class_map *map;
>>> + int idx;
>>> +
>>> + list_for_each_entry(map, &dt->maps, link) {
>>> + idx = match_string(map->class_names, map->length, class_string);
>>> + if (idx >= 0) {
>>> + *class_id = idx + map->base;
>>> + return map;
>>> + }
>>> + }
>>> + *class_id = -ENOENT;
>>> + return NULL;
>>> +}
>>> +
>>> +#define __outvar /* filled by callee */
>>> /*
>>> * Search the tables for _ddebug's which match the given `query' and
>>> * apply the `flags' and `mask' to them. Returns number of matching
>>> @@ -159,6 +178,8 @@ static int ddebug_change(const struct ddebug_query *query,
>>> unsigned int newflags;
>>> unsigned int nfound = 0;
>>> struct flagsbuf fbuf, nbuf;
>>> + struct ddebug_class_map *map = NULL;
>>> + int __outvar valid_class;
>>>
>>> /* search for matching ddebugs */
>>> mutex_lock(&ddebug_lock);
>>> @@ -169,9 +190,22 @@ static int ddebug_change(const struct ddebug_query *query,
>>> !match_wildcard(query->module, dt->mod_name))
>>> continue;
>>>
>>> + if (query->class_string) {
>>> + map = ddebug_find_valid_class(dt, query->class_string, &valid_class);
>>> + if (!map)
>>> + continue;
>>
>> So remove the else here.
>>
>>> + } else {
>>> + /* constrain query, do not touch class'd callsites */
>>> + valid_class = _DPRINTK_CLASS_DFLT;
>>> + }
>>> +
>>> for (i = 0; i < dt->num_ddebugs; i++) {
>>> struct _ddebug *dp = &dt->ddebugs[i];
>>>
>>> + /* match site against query-class */
>>> + if (dp->class_id != valid_class)
>>
>> And then make this: if (query->class_string && (dp->class_id != valid_class))
>>
>> thoughts?
>>
>>
>>> + continue;
>>> +> /* match against the source filename */
>>> if (query->filename &&
>>> !match_wildcard(query->filename, dp->filename) &&
>>> @@ -420,6 +454,8 @@ static int ddebug_parse_query(char *words[], int nwords,
>>> } else if (!strcmp(keyword, "line")) {
>>> if (parse_linerange(query, arg))
>>> return -EINVAL;
>>> + } else if (!strcmp(keyword, "class")) {
>>> + rc = check_set(&query->class_string, arg, "class");
>>> } else {
>>> pr_err("unknown keyword \"%s\"\n", keyword);
>>> return -EINVAL;
>>> @@ -854,6 +890,20 @@ static void *ddebug_proc_next(struct seq_file *m, void *p, loff_t *pos)
>>> return dp;
>>> }
>>>
>>> +#define class_in_range(class_id, map) \
>>> + (class_id >= map->base && class_id < map->base + map->length)
>>> +
>>> +static const char *ddebug_class_name(struct ddebug_iter *iter, struct _ddebug *dp)
>>> +{
>>> + struct ddebug_class_map *map;
>>> +
>>> + list_for_each_entry(map, &iter->table->maps, link)
>>> + if (class_in_range(dp->class_id, map))
>>> + return map->class_names[dp->class_id - map->base];
>>> +
>>> + return NULL;
>>> +}
>>> +
>>> /*
>>> * Seq_ops show method. Called several times within a read()
>>> * call from userspace, with ddebug_lock held. Formats the
>>> @@ -865,6 +915,7 @@ static int ddebug_proc_show(struct seq_file *m, void *p)
>>> struct ddebug_iter *iter = m->private;
>>> struct _ddebug *dp = p;
>>> struct flagsbuf flags;
>>> + char const *class;
>>>
>>> if (p == SEQ_START_TOKEN) {
>>> seq_puts(m,
>>> @@ -877,7 +928,16 @@ static int ddebug_proc_show(struct seq_file *m, void *p)
>>> iter->table->mod_name, dp->function,
>>> ddebug_describe_flags(dp->flags, &flags));
>>> seq_escape_str(m, dp->format, ESCAPE_SPACE, "\t\r\n\"");
>>> - seq_puts(m, "\"\n");
>>> + seq_puts(m, "\"");
>>> +
>>> + if (dp->class_id != _DPRINTK_CLASS_DFLT) {
>>> + class = ddebug_class_name(iter, dp);
>>> + if (class)
>>> + seq_printf(m, " class:%s", class);
>>> + else
>>> + seq_printf(m, " class unknown, _id:%d", dp->class_id);
>>> + }
>>> + seq_puts(m, "\n");
>>>
>>> return 0;
>>> }
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