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Message-Id: <20240723063258.2240610-1-zhengyejian@huaweicloud.com>
Date: Tue, 23 Jul 2024 14:32:53 +0800
From: Zheng Yejian <zhengyejian@...weicloud.com>
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Subject: [PATCH v2 0/5] kallsyms: Emit symbol for holes in text and fix weak function issue
Background of this patch set can be found in v1:
https://lore.kernel.org/all/20240613133711.2867745-1-zhengyejian1@huawei.com/
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@mail.gmail.com/
- 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@mail.gmail.com/
- 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@mail.gmail.com/
- 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
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