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    SubjectRe: [PATCH v6 17/57] dyndbg: validate class FOO by checking with module
    On Wed, Sep 7, 2022 at 12:19 PM Jason Baron <jbaron@akamai.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.



    > 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 ?

    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@gmail.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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