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Date: Fri, 3 May 2024 16:09:40 +0200 From: Thomas Weißschuh <linux@...ssschuh.net> To: Joel Granados <j.granados@...sung.com> Cc: Luis Chamberlain <mcgrof@...nel.org>, Kees Cook <keescook@...omium.org>, Eric Dumazet <edumazet@...gle.com>, Dave Chinner <david@...morbit.com>, linux-fsdevel@...r.kernel.org, netdev@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org, linux-mm@...ck.org, linux-security-module@...r.kernel.org, bpf@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org, linux-xfs@...r.kernel.org, linux-trace-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org, netfilter-devel@...r.kernel.org, coreteam@...filter.org, kexec@...ts.infradead.org, linux-hardening@...r.kernel.org, bridge@...ts.linux.dev, lvs-devel@...r.kernel.org, linux-rdma@...r.kernel.org, rds-devel@....oracle.com, linux-sctp@...r.kernel.org, linux-nfs@...r.kernel.org, apparmor@...ts.ubuntu.com Subject: Re: [PATCH v3 00/11] sysctl: treewide: constify ctl_table argument of sysctl handlers Hey Joel, On 2024-05-03 11:03:32+0000, Joel Granados wrote: > Here is my feedback for your outstanding constification patches [1] and [2]. Thanks! > # You need to split the patch > The answer that you got from Jakub in the network subsystem is very clear and > baring a change of heart from the network folks, this will go in as but as a > split patchset. Please split it considering the following: > 1. Create a different patchset for drivers/, fs/, kernel/, net, and a > miscellaneous that includes whatever does not fit into the others. > 2. Consider that this might take several releases. > 3. Consider the following sufix for the interim function name "_const". Like in > kfree_const. Please not "_new". Ack. "_new" was an intentionally unacceptable placeholder. > 4. Please publish the final result somewhere. This is important so someone can > take over in case you need to stop. Will do. Both for each single series and a combination of all of them. > 5. Consistently mention the motivation in your cover letters. I specify more > further down in "#Motivation". > 6. Also mention that this is part of a bigger effort (like you did in your > original cover letters). I would include [3,4,5,6] > 7. Include a way to show what made it into .rodata. I specify more further down > in "#Show the move". > > # Motivation > As I read it, the motivation for these constification efforts are: > 1. It provides increased safety: Having things in .rodata section reduces the > attack surface. This is especially relevant for structures that have function > pointers (like ctl_table); having these in .rodata means that these pointers > always point to the "intended" function and cannot be changed. > 2. Compiler optimizations: This was just a comment in the patchsets that I have > mentioned ([3,4,5]). Do you know what optimizations specifically? Does it > have to do with enhancing locality for the data in .rodata? Do you have other > specific optimizations in mind? I don't know about anything that would make it faster. It's more about safety and transmission of intent to API users, especially callback implementers. > 3. Readability: because it is easier to know up-front that data is not supposed > to change or its obvious that a function is re-entrant. Actually a lot of the > readability reasons is about knowing things "up-front". > As we move forward with the constification in sysctl, please include a more > detailed motivation in all your cover letters. This helps maintainers (that > don't have the context) understand what you are trying to do. It does not need > to be my three points, but it should be more than just "put things into > .rodata". Please tell me if I have missed anything in the motivation. Will do. > # Show the move > I created [8] because there is no easy way to validate which objects made it > into .rodata. I ran [8] for your Dec 2nd patcheset [7] and there are less in > .rodata than I expected (the results are in [9]) Why is that? Is it something > that has not been posted to the lists yet? Constifying the APIs only *allows* the actual table to be constified themselves. Then each table definition will have to be touched and "const" added. See patches 17 and 18 in [7] for two examples. Some tables in net/ are already "const" as the static definitions are never registered themselves but only their copies are. This seems to explain your findings. > Best Thanks! > [1] https://lore.kernel.org/all/20240423-sysctl-const-handler-v3-0-e0beccb836e2@weissschuh.net/ > [2] https://lore.kernel.org/all/20240418-sysctl-const-table-arg-v2-1-4012abc31311@weissschuh.net > [3] [PATCH v2 00/14] ASoC: Constify local snd_sof_dsp_ops > https://lore.kernel.org/all/20240426-n-const-ops-var-v2-0-e553fe67ae82@kernel.org > [4] [PATCH v2 00/19] backlight: Constify lcd_ops > https://lore.kernel.org/all/20240424-video-backlight-lcd-ops-v2-0-1aaa82b07bc6@kernel.org > [5] [PATCH 1/4] iommu: constify pointer to bus_type > https://lore.kernel.org/all/20240216144027.185959-1-krzysztof.kozlowski@linaro.org > [6] [PATCH 00/29] const xattr tables > https://lore.kernel.org/all/20230930050033.41174-1-wedsonaf@gmail.com > [7] https://lore.kernel.org/all/20231204-const-sysctl-v2-0-7a5060b11447@weissschuh.net/ > > [8] [snip] > [9] > section: .rodata obj_name : kern_table > section: .rodata obj_name : sysctl_mount_point > section: .rodata obj_name : addrconf_sysctl > section: .rodata obj_name : ax25_param_table > section: .rodata obj_name : mpls_table > section: .rodata obj_name : mpls_dev_table > section: .data obj_name : sld_sysctls > section: .data obj_name : kern_panic_table > section: .data obj_name : kern_exit_table > section: .data obj_name : vm_table > section: .data obj_name : signal_debug_table > section: .data obj_name : usermodehelper_table > section: .data obj_name : kern_reboot_table > section: .data obj_name : user_table > section: .bss obj_name : sched_core_sysctls > section: .data obj_name : sched_fair_sysctls > section: .data obj_name : sched_rt_sysctls > section: .data obj_name : sched_dl_sysctls > section: .data obj_name : printk_sysctls > section: .data obj_name : pid_ns_ctl_table_vm > section: .data obj_name : seccomp_sysctl_table > section: .data obj_name : uts_kern_table > section: .data obj_name : vm_oom_kill_table > section: .data obj_name : vm_page_writeback_sysctls > section: .data obj_name : page_alloc_sysctl_table > section: .data obj_name : hugetlb_table > section: .data obj_name : fs_stat_sysctls > section: .data obj_name : fs_exec_sysctls > section: .data obj_name : fs_pipe_sysctls > section: .data obj_name : namei_sysctls > section: .data obj_name : fs_dcache_sysctls > section: .data obj_name : inodes_sysctls > section: .data obj_name : fs_namespace_sysctls > section: .data obj_name : dnotify_sysctls > section: .data obj_name : inotify_table > section: .data obj_name : epoll_table > section: .data obj_name : aio_sysctls > section: .data obj_name : locks_sysctls > section: .data obj_name : coredump_sysctls > section: .data obj_name : fs_shared_sysctls > section: .data obj_name : fs_dqstats_table > section: .data obj_name : root_table > section: .data obj_name : pty_table > section: .data obj_name : xfs_table > section: .data obj_name : ipc_sysctls > section: .data obj_name : key_sysctls > section: .data obj_name : kernel_io_uring_disabled_table > section: .data obj_name : tty_table > section: .data obj_name : random_table > section: .data obj_name : scsi_table > section: .data obj_name : iwcm_ctl_table > section: .data obj_name : net_core_table > section: .data obj_name : netns_core_table > section: .bss obj_name : nf_log_sysctl_table > section: .data obj_name : nf_log_sysctl_ftable > section: .data obj_name : vs_vars > section: .data obj_name : vs_vars_table > section: .data obj_name : ipv4_route_netns_table > section: .data obj_name : ipv4_route_table > section: .data obj_name : ip4_frags_ns_ctl_table > section: .data obj_name : ip4_frags_ctl_table > section: .data obj_name : ctl_forward_entry > section: .data obj_name : ipv4_table > section: .data obj_name : ipv4_net_table > section: .data obj_name : unix_table > section: .data obj_name : ipv6_route_table_template > section: .data obj_name : ipv6_icmp_table_template > section: .data obj_name : ip6_frags_ns_ctl_table > section: .data obj_name : ip6_frags_ctl_table > section: .data obj_name : ipv6_table_template > section: .data obj_name : ipv6_rotable > section: .data obj_name : sctp_net_table > section: .data obj_name : sctp_table > section: .data obj_name : smc_table > section: .data obj_name : lowpan_frags_ns_ctl_table > section: .data obj_name : lowpan_frags_ctl_table
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