Messages in this thread | | | Date | Thu, 18 Mar 2021 14:58:09 -0700 | From | Kees Cook <> | Subject | Re: [RFC PATCH] devres: better type safety with devm_*_action() |
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On Thu, Mar 18, 2021 at 09:30:12PM +0100, Rasmus Villemoes wrote: > On 10/03/2021 00.59, Rasmus Villemoes wrote: > > [quoting in full for context to the new CCs] > > > With a little MacroMagic(tm), we can allow users to pass a pointer to > > a function that actually takes the type of the data argument, instead > > of forcing the function to have prototype void (*)(void *). Of course, > > we must still accept such functions. > > > > This can provide a little more type safety in that we get fewer > > implicit casts to and from void* - as a random example, > > gpio_mockup_dispose_mappings in drivers/gpio/gpio-mockup.c could take > > a "struct gpio_mockup_chip *chip" directly. > > > > Moreover, when the action is some "external" API, there will in many > > cases no longer be a need for a trivial local wrapper - > > e.g. drivers/watchdog/cadence_wdt.c could just use > > clk_disable_unprepare directly and avoid defining > > cdns_clk_disable_unprepare. > > > > Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk> > > --- > > drivers/base/devres.c | 32 +++++++++++++++++++++++--------- > > include/linux/device.h | 36 ++++++++++++++++++++++++++++++++---- > > 2 files changed, 55 insertions(+), 13 deletions(-) > > > > diff --git a/drivers/base/devres.c b/drivers/base/devres.c > > index fb9d5289a620..97ebd26bc44a 100644 > > --- a/drivers/base/devres.c > > +++ b/drivers/base/devres.c > > @@ -728,15 +728,25 @@ static void devm_action_release(struct device *dev, void *res) > > } > > > > /** > > - * devm_add_action() - add a custom action to list of managed resources > > + * __devm_add_action() - add a custom action to list of managed resources > > * @dev: Device that owns the action > > * @action: Function that should be called > > * @data: Pointer to data passed to @action implementation > > * > > * This adds a custom action to the list of managed resources so that > > * it gets executed as part of standard resource unwinding. > > + * > > + * Do not call directly, but use the the macro wrapper > > + * devm_add_action, whose "prototype" is > > + * > > + * devm_add_action(struct device *dev, void (*action)(T *), T *data) > > + * > > + * This allows use of type-correct callbacks and can avoid wrapping > > + * external APIs. For example, if the data item is a "struct clk *", one > > + * can use clk_disable_unprepare directly as the action instead of > > + * creating a local wrapper taking a "void *" argument. > > */ > > -int devm_add_action(struct device *dev, void (*action)(void *), void *data) > > +int __devm_add_action(struct device *dev, void (*action)(void *), void *data) > > { > > struct action_devres *devres; > > > > @@ -751,18 +761,20 @@ int devm_add_action(struct device *dev, void (*action)(void *), void *data) > > devres_add(dev, devres); > > return 0; > > } > > -EXPORT_SYMBOL_GPL(devm_add_action); > > +EXPORT_SYMBOL_GPL(__devm_add_action); > > > > /** > > - * devm_remove_action() - removes previously added custom action > > + * __devm_remove_action() - removes previously added custom action > > * @dev: Device that owns the action > > * @action: Function implementing the action > > * @data: Pointer to data passed to @action implementation > > * > > * Removes instance of @action previously added by devm_add_action(). > > * Both action and data should match one of the existing entries. > > + * > > + * Use the macro wrapper devm_remove_action, see __devm_add_action for details. > > */ > > -void devm_remove_action(struct device *dev, void (*action)(void *), void *data) > > +void __devm_remove_action(struct device *dev, void (*action)(void *), void *data) > > { > > struct action_devres devres = { > > .data = data, > > @@ -772,10 +784,10 @@ void devm_remove_action(struct device *dev, void (*action)(void *), void *data) > > WARN_ON(devres_destroy(dev, devm_action_release, devm_action_match, > > &devres)); > > } > > -EXPORT_SYMBOL_GPL(devm_remove_action); > > +EXPORT_SYMBOL_GPL(__devm_remove_action); > > > > /** > > - * devm_release_action() - release previously added custom action > > + * __devm_release_action() - release previously added custom action > > * @dev: Device that owns the action > > * @action: Function implementing the action > > * @data: Pointer to data passed to @action implementation > > @@ -783,8 +795,10 @@ EXPORT_SYMBOL_GPL(devm_remove_action); > > * Releases and removes instance of @action previously added by > > * devm_add_action(). Both action and data should match one of the > > * existing entries. > > + * > > + * Use the macro wrapper devm_release_action, see __devm_add_action for details. > > */ > > -void devm_release_action(struct device *dev, void (*action)(void *), void *data) > > +void __devm_release_action(struct device *dev, void (*action)(void *), void *data) > > { > > struct action_devres devres = { > > .data = data, > > @@ -795,7 +809,7 @@ void devm_release_action(struct device *dev, void (*action)(void *), void *data) > > &devres)); > > > > } > > -EXPORT_SYMBOL_GPL(devm_release_action); > > +EXPORT_SYMBOL_GPL(__devm_release_action); > > > > /* > > * Managed kmalloc/kfree > > diff --git a/include/linux/device.h b/include/linux/device.h > > index ba660731bd25..c924612bfefd 100644 > > --- a/include/linux/device.h > > +++ b/include/linux/device.h > > @@ -250,11 +250,39 @@ void __iomem *devm_of_iomap(struct device *dev, > > resource_size_t *size); > > > > /* allows to add/remove a custom action to devres stack */ > > -int devm_add_action(struct device *dev, void (*action)(void *), void *data); > > -void devm_remove_action(struct device *dev, void (*action)(void *), void *data); > > -void devm_release_action(struct device *dev, void (*action)(void *), void *data); > > > > -static inline int devm_add_action_or_reset(struct device *dev, > > +/* > > + * +0 forces the expression to decay to a function pointer. We cannot > > + * just put an & in front as callers may already include that. > > + */ > > +#define devm_action_typecheck(action, data) \ > > + static_assert(__same_type(action + 0, void (*)(void *)) || \ > > + __same_type(action + 0, void (*)(typeof(data)))) > > + > > +#define devm_add_action(dev, action, data) ({ \ > > + devm_action_typecheck(action, data); \ > > + __devm_add_action(dev, (void (*)(void *))action, data); \ > > +}) > > +#define devm_remove_action(dev, action, data) ({ \ > > + devm_action_typecheck(action, data); \ > > + __devm_remove_action(dev, (void (*)(void *))action, data); \ > > +}) > > +#define devm_release_action(dev, action, data) ({ \ > > + devm_action_typecheck(action, data); \ > > + __devm_release_action(dev, (void (*)(void *))action, data); \ > > +}) > > + > > + > > +int __devm_add_action(struct device *dev, void (*action)(void *), void *data); > > +void __devm_remove_action(struct device *dev, void (*action)(void *), void *data); > > +void __devm_release_action(struct device *dev, void (*action)(void *), void *data); > > + > > +#define devm_add_action_or_reset(dev, action, data) ({ \ > > + devm_action_typecheck(action, data); \ > > + __devm_add_action_or_reset(dev, (void (*)(void *))action, data); \ > > +}) > > + > > +static inline int __devm_add_action_or_reset(struct device *dev, > > void (*action)(void *), void *data) > > { > > int ret; > > > > So, this would likely crash and burn under CFI if I understand > correctly. Is there any way to make such "polymorphic" callbacks with > type-checking done via macros coexist with CFI? I mean, it's a bit sad > that in order to have the sanity checks done by CFI, one has to force > everything through functions that take void* instead of the type that > they really act on.
Yeah, that'll light up CFI. ;) Why not stick with the existing standard of callbacks, which is to pass the object pointer the callback is attached to (as done with timer_struct, etc)?
As in the prototype should be just
void callback(struct device *dev);
or if we absolutely must have a "data" argument (it'd be better to have the data directly associated with the struct device):
void callback(struct device *dev, void *data);
-- Kees Cook
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