Messages in this thread | | | Date | Wed, 9 Aug 2023 11:30:21 -0400 | From | Steven Rostedt <> | Subject | Re: [PATCH v3 3/3] list_debug: Introduce CONFIG_DEBUG_LIST_MINIMAL |
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On Wed, 9 Aug 2023 11:57:19 +0200 Marco Elver <elver@google.com> wrote:
> static __always_inline bool __list_add_valid(struct list_head *new, > struct list_head *prev, > struct list_head *next) > { > - return __list_add_valid_or_report(new, prev, next); > + bool ret = true; > + > + if (IS_ENABLED(CONFIG_HARDEN_LIST)) { > + /* > + * With the hardening version, elide checking if next and prev > + * are NULL, since the immediate dereference of them below would > + * result in a fault if NULL. > + * > + * With the reduced set of checks, we can afford to inline the > + * checks, which also gives the compiler a chance to elide some > + * of them completely if they can be proven at compile-time. If > + * one of the pre-conditions does not hold, the slow-path will > + * show a report which pre-condition failed. > + */ > + if (likely(next->prev == prev && prev->next == next && new != prev && new != next)) > + return true; > + ret = false; > + } > + > + ret &= __list_add_valid_or_report(new, prev, next); > + return ret; > }
I would actually prefer DEBUG_LIST to select HARDEN_LIST and not the other way around. It logically doesn't make sense that HARDEN_LIST would select DEBUG_LIST. That is, I could by default want HARDEN_LIST always on, but not DEBUG_LIST (because who knows, it may add other features I don't want). But then, I may have stumbled over something and want more info, and enable DEBUG_LIST (while still having HARDEN_LIST) enabled.
I think you are looking at this from an implementation perspective and not the normal developer one.
This would mean the above function should get enabled by CONFIG_HARDEN_LIST (and CONFIG_DEBUG would select CONFIG_HARDEN) and would look more like:
static __always_inline bool __list_add_valid(struct list_head *new, struct list_head *prev, struct list_head *next) { bool ret = true;
if (!IS_ENABLED(CONFIG_DEBUG_LIST)) { /* * With the hardening version, elide checking if next and prev * are NULL, since the immediate dereference of them below would * result in a fault if NULL. * * With the reduced set of checks, we can afford to inline the * checks, which also gives the compiler a chance to elide some * of them completely if they can be proven at compile-time. If * one of the pre-conditions does not hold, the slow-path will * show a report which pre-condition failed. */ if (likely(next->prev == prev && prev->next == next && new != prev && new != next)) return true; ret = false; }
ret &= __list_add_valid_or_report(new, prev, next); return ret; }
That is, if DEBUG_LIST is enabled, we always call the __list_add_valid_or_report(), but if only HARDEN_LIST is enabled, then we do the shortcut.
-- Steve
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