From: Čestmír Kalina <ckalina@xxxxxxxxxx> kabi: macros for intentional kABI breakage Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2024595 Upstream Status: RHEL only commit 69bc4518f92fcaafabc846d31e568eedd65264d9 Author: Jiri Benc <jbenc@xxxxxxxxxx> Date: Wed, 19 Feb 2020 12:04:22 -0500 Occasionally, we modify a struct that is included from a whitelisted function through a chain of other structs but the modified struct is internal to the kernel and 3rd party modules are not allowed to access it. In such cases, it is safe and preferable to modify that struct without paying attention to the kABI checksums. An example of this is bpf rebases: bpf is not considered kABI stable and 3rd party modules may not use it without recompilation between releases. However, through a chain of structs, some bpf structs are part of kABI checksum computations. Given the high volume of changes upstream in the bpf code, we need to keep the added fields at the same places as in upstream to ensure maintainability of RHEL code. Another example is PHY rebases. Currently, the code solves it by using the RH_KABI_EXTEND macro. Although it is technically okay and the code will work, it is not the right macro to use, as the RH_KABI macro usage is expected to also serve as a documentation of the kABI workaround used. In particular, RH_KABI_EXTEND means the structure was safely extended, preserving kABI stability. Which is not the case here, we did break kABI (but it was okay to break it). Introduce new macros that convey this meaning and use them in all places where previously less fitting macros were used. RH-Signed-off-by: Jiri Benc <jbenc@xxxxxxxxxx> Signed-off-by: Čestmír Kalina <ckalina@xxxxxxxxxx> Signed-off-by: Prarit Bhargava <prarit@xxxxxxxxxx> diff --git a/include/linux/rh_kabi.h b/include/linux/rh_kabi.h index blahblah..blahblah 100644 --- a/include/linux/rh_kabi.h +++ b/include/linux/rh_kabi.h @@ -2,7 +2,7 @@ * rh_kabi.h - Red Hat kABI abstraction header * * Copyright (c) 2014 Don Zickus - * Copyright (c) 2015-2018 Jiri Benc + * Copyright (c) 2015-2020 Jiri Benc * Copyright (c) 2015 Sabrina Dubroca, Hannes Frederic Sowa * Copyright (c) 2016-2018 Prarit Bhargava * Copyright (c) 2017 Paolo Abeni, Larry Woodman @@ -140,6 +140,30 @@ * of the size is not allowed and would constitute a silent kABI breakage. * Beware that the RH_KABI_EXCLUDE macro does not do any size checks. * + * RH_KABI_BROKEN_INSERT + * RH_KABI_BROKEN_REMOVE + * Insert a field to the middle of a struct / delete a field from a struct. + * Note that this breaks kABI! It can be done only when it's certain that + * no 3rd party driver can validly reach into the struct. A typical + * example is a struct that is: both (a) referenced only through a long + * chain of pointers from another struct that is part of a whitelisted + * symbol and (b) kernel internal only, it should have never been visible + * to genksyms in the first place. + * + * Another example are structs that are explicitly exempt from kABI + * guarantee but we did not have enough foresight to use RH_KABI_EXCLUDE. + * In this case, the warning for RH_KABI_EXCLUDE applies. + * + * A detailed explanation of correctness of every RH_KABI_BROKEN_* macro + * use is especially important. + * + * RH_KABI_BROKEN_INSERT_BLOCK + * RH_KABI_BROKEN_REMOVE_BLOCK + * A version of RH_KABI_BROKEN_INSERT / REMOVE that allows multiple fields + * to be inserted or removed together. All fields need to be terminated + * by ';' inside(!) the macro parameter. The macro itself must not be + * terminated by ';'. + * */ #undef linux @@ -154,6 +178,10 @@ # define RH_KABI_RENAME(_orig, _new) _orig # define RH_KABI_HIDE_INCLUDE(_file) <linux/rh_kabi.h> # define RH_KABI_FAKE_INCLUDE(_file) _file +# define RH_KABI_BROKEN_INSERT(_new) +# define RH_KABI_BROKEN_REMOVE(_orig) _orig; +# define RH_KABI_BROKEN_INSERT_BLOCK(_new) +# define RH_KABI_BROKEN_REMOVE_BLOCK(_orig) _orig # define _RH_KABI_DEPRECATE(_type, _orig) _type _orig # define _RH_KABI_DEPRECATE_FN(_type, _orig, _args...) _type (*_orig)(_args) @@ -172,6 +200,10 @@ # define RH_KABI_RENAME(_orig, _new) _new # define RH_KABI_HIDE_INCLUDE(_file) _file # define RH_KABI_FAKE_INCLUDE(_file) <linux/rh_kabi.h> +# define RH_KABI_BROKEN_INSERT(_new) _new; +# define RH_KABI_BROKEN_REMOVE(_orig) +# define RH_KABI_BROKEN_INSERT_BLOCK(_new) _new +# define RH_KABI_BROKEN_REMOVE_BLOCK(_orig) #if IS_BUILTIN(CONFIG_RH_KABI_SIZE_ALIGN_CHECKS) -- https://gitlab.com/cki-project/kernel-ark/-/merge_requests/1530 _______________________________________________ kernel mailing list -- kernel@xxxxxxxxxxxxxxxxxxxxxxx To unsubscribe send an email to kernel-leave@xxxxxxxxxxxxxxxxxxxxxxx Fedora Code of Conduct: https://docs.fedoraproject.org/en-US/project/code-of-conduct/ List Guidelines: https://fedoraproject.org/wiki/Mailing_list_guidelines List Archives: https://lists.fedoraproject.org/archives/list/kernel@xxxxxxxxxxxxxxxxxxxxxxx Do not reply to spam on the list, report it: https://pagure.io/fedora-infrastructure
