From a6231d1993367cf48a9c5f1adc295a5a8b1c5731 Mon Sep 17 00:00:00 2001 From: Alexey Dobriyan Date: Tue, 14 May 2019 15:44:40 -0700 Subject: [PATCH] exec: move struct linux_binprm::buf struct linux_binprm::buf is the first field and it is exactly 128 bytes in size. It means that on x86_64 all accesses to other fields will go though [r64 + disp32] addressing mode which is 3 bytes bloatier than [r64 + disp8] addressing mode. Given that accesses to other fields outnumber accesses to ->buf, move it down. Space savings (x86_64 defconfig): more on distro configs because LSMs actively dereference "bprm" but do not care about first 128 bytes of the executable itself. add/remove: 0/0 grow/shrink: 0/24 up/down: 0/-492 (-492) Function old new delta selinux_bprm_committing_creds 552 549 -3 finalize_exec 94 91 -3 __audit_log_bprm_fcaps 283 280 -3 __audit_bprm 39 36 -3 perf_trace_sched_process_exec 347 341 -6 install_exec_creds 105 99 -6 cap_bprm_set_creds.cold 60 54 -6 would_dump 137 128 -9 load_script 637 628 -9 bprm_change_interp 61 52 -9 trace_event_raw_event_sched_process_exec 260 250 -10 search_binary_handler 255 240 -15 remove_arg_zero 295 277 -18 free_bprm 119 101 -18 prepare_binprm 379 360 -19 setup_new_exec 336 315 -21 flush_old_exec 1638 1617 -21 copy_strings.isra 746 724 -22 setup_arg_pages 559 530 -29 load_misc_binary 1151 1118 -33 selinux_bprm_set_creds 792 753 -39 load_elf_binary 11111 11072 -39 cap_bprm_set_creds 1496 1454 -42 __do_execve_file.isra 2395 2286 -109 Link: http://lkml.kernel.org/r/20190421165025.GA26843@avx2 Signed-off-by: Alexey Dobriyan Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/binfmts.h | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/include/linux/binfmts.h b/include/linux/binfmts.h index 688ab0de7810..b40fc633f3be 100644 --- a/include/linux/binfmts.h +++ b/include/linux/binfmts.h @@ -15,7 +15,6 @@ struct filename; * This structure is used to hold the arguments that are used when loading binaries. */ struct linux_binprm { - char buf[BINPRM_BUF_SIZE]; #ifdef CONFIG_MMU struct vm_area_struct *vma; unsigned long vma_pages; @@ -64,6 +63,8 @@ struct linux_binprm { unsigned long loader, exec; struct rlimit rlim_stack; /* Saved RLIMIT_STACK used during exec. */ + + char buf[BINPRM_BUF_SIZE]; } __randomize_layout; #define BINPRM_FLAGS_ENFORCE_NONDUMP_BIT 0 -- 2.30.2