Background of this patch set can be found in v1: https://lore.kernel.org/all/20240613133711.2867745-1-zhengyejian1@xxxxxxxxxx/ Here add a reproduction to show the impact to livepatch: 1. Add following hack to make livepatch-sample.ko do patch on do_one_initcall() which has an overriden weak function behind in vmlinux, then print the actually used __fentry__ location: diff --git a/kernel/livepatch/patch.c b/kernel/livepatch/patch.c index 90408500e5a3..20b75e7b1771 100644 --- a/kernel/livepatch/patch.c +++ b/kernel/livepatch/patch.c @@ -173,6 +173,8 @@ static int klp_patch_func(struct klp_func *func) unsigned long ftrace_loc; ftrace_loc = ftrace_location((unsigned long)func->old_func); + pr_info("%s: old_func=%pS ftrace_loc=%pS (%lx)\n", __func__, + func->old_func, (void *)ftrace_loc, ftrace_loc); if (!ftrace_loc) { pr_err("failed to find location for function '%s'\n", func->old_name); diff --git a/samples/livepatch/livepatch-sample.c b/samples/livepatch/livepatch-sample.c index cd76d7ebe598..c6e8e78e23b8 100644 --- a/samples/livepatch/livepatch-sample.c +++ b/samples/livepatch/livepatch-sample.c @@ -38,7 +38,7 @@ static int livepatch_cmdline_proc_show(struct seq_file *m, void *v) static struct klp_func funcs[] = { { - .old_name = "cmdline_proc_show", + .old_name = "do_one_initcall", .new_func = livepatch_cmdline_proc_show, }, { } }; 2. We can see the size of do_one_initcall() is 0x27e: $ nm -nS vmlinux | grep do_one_initcall ffffffff810021e0 000000000000027e T do_one_initcall 3. Insert the livepatch ko, the expected ftrace_loc is do_one_initcall+0x4/0x27e but actually do_one_initcall+0x294/0x2c0 which is invalid, also its size is inaccurate. Then this livepatch can not properly work!!! # insmod livepatch-sample.ko [ 17.942451] livepatch: klp_patch_func: old_func=do_one_initcall+0x0/0x2c0 ftrace_loc=do_one_initcall+0x294/0x2c0 (ffffffff81002474) # # cat /sys/kernel/tracing/available_filter_functions_addrs | grep ffffffff81002474 ffffffff81002474 __ftrace_invalid_address___660 After this patch, this issue is gone: # insmod livepatch-sample.ko [ 42.408632] livepatch: klp_patch_func: old_func=do_one_initcall+0x0/0x27e ftrace_loc=do_one_initcall+0x4/0x27e (ffffffff810021e4) # cat /sys/kernel/tracing/available_filter_functions_addrs | grep ffffffff810021e4 ffffffff810021e4 do_one_initcall # cat /sys/kernel/tracing/enabled_functions do_one_initcall (1) I M tramp: 0xffffffffa0020000 (klp_ftrace_handler+0x0/0x258)->klp_ftrace_handler+0x0/0x258 Changes: v1->v2: - Drop patch which titled "kallsyms: Optimize multiple times of realloc() to one time of malloc()" as suggested by Masahiro; Link: https://lore.kernel.org/all/CAK7LNAQkSnZ1nVXiZH9kg52H-A_=urcsv-W7wGXvunMGhGX8Vw@xxxxxxxxxxxxxx/ - Changes in PATCH 1/5: - Change may_exist_hole_after_symbol() to has_hole() and return bool type; - User realloc instead of malloc another table in emit_hole_symbols(); Link: https://lore.kernel.org/all/CAK7LNAQaLc6aDK85qQtPHoCkQSGyL-TxXjpgJTfehe2Q1=jMSA@xxxxxxxxxxxxxx/ - Use empty symbol type/name as a special case to represent the hole instead of using symbol "t__hole_symbol_XXXXX"; Link: https://lore.kernel.org/all/CAK7LNARiR5z9hPRG932T7YjRWqkX_qZ7WKmbxx7iTo2w5YJojQ@xxxxxxxxxxxxxx/ - Changes in PATCH 3/5: - Now name of hole symbol is NULL, so if __fentry__ is located in a hole, kallsyms_lookup() find an NULL name then will return 0, so drop the needless kallsyms_is_hole_symbol(). Zheng Yejian (5): kallsyms: Emit symbol at the holes in the text module: kallsyms: Determine exact function size ftrace: Skip invalid __fentry__ in ftrace_process_locs() ftrace: Fix possible out-of-bound issue in ftrace_process_locs() ftrace: Revert the FTRACE_MCOUNT_MAX_OFFSET workaround arch/powerpc/include/asm/ftrace.h | 7 -- arch/x86/include/asm/ftrace.h | 7 -- include/linux/module.h | 14 +++ kernel/module/kallsyms.c | 42 ++++++-- kernel/trace/ftrace.c | 171 ++++++------------------------ scripts/kallsyms.c | 95 ++++++++++++++++- scripts/link-vmlinux.sh | 4 +- scripts/mksysmap | 2 +- 8 files changed, 173 insertions(+), 169 deletions(-) -- 2.25.1
