Re: [PATCH v4 06/10] modpost: Add modinfo flag to livepatch modules

[Masahiro Yamada <yamada.masahiro@socionext.com>]

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Hi Joe,


On Thu, May 9, 2019 at 11:39 PM Joe Lawrence <joe.lawrence@redhat.com> wrote:
>
> From: Miroslav Benes <mbenes@suse.cz>
>
> Currently, livepatch infrastructure in the kernel relies on
> MODULE_INFO(livepatch, "Y") statement in a livepatch module. Then the
> kernel module loader knows a module is indeed livepatch module and can
> behave accordingly.
>
> klp-convert, on the other hand relies on LIVEPATCH_* statement in the
> module's Makefile for exactly the same reason.
>
> Remove dependency on modinfo and generate MODULE_INFO flag
> automatically in modpost when LIVEPATCH_* is defined in the module's
> Makefile. Generate a list of all built livepatch modules based on
> the .livepatch file and store it in (MODVERDIR)/livepatchmods. Give
> this list as an argument for modpost which will use it to identify
> livepatch modules.
>
> As MODULE_INFO is no longer needed, remove it.


I do not understand this patch.
This makes the implementation so complicated.

I think MODULE_INFO(livepatch, "Y") is cleaner than
LIVEPATCH_* in Makefile.


How about this approach?


[1] Make modpost generate the list of livepatch modules.
    (livepatch-modules)

[2] Generate Symbols.list in scripts/Makefile.modpost
    (vmlinux + modules excluding livepatch-modules)

[3] Run klp-convert for modules in livepatch-modules.


If you do this, you can remove most of the build system hacks
can't you?


I attached an example implementation for [1].

Please check whether this works.

Thanks.



-- 
Best Regards
Masahiro Yamada

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From 85571430aa12cd19a75cbc856da1092199876e6a Mon Sep 17 00:00:00 2001
From: Masahiro Yamada <yamada.masahiro@socionext.com>
Date: Wed, 31 Jul 2019 14:51:29 +0900
Subject: [PATCH] livepatch: make modpost generate the list of livepatch
 modules

Reverse the livepatch-modules direction.

The modpost generates the livepatch-modules file instead of
Makefile feeding it to modpost.

The implementation just mimics write_dump().

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
---
 scripts/Makefile.modpost |  3 ++-
 scripts/mod/modpost.c    | 28 ++++++++++++++++++++++++++--
 scripts/mod/modpost.h    |  1 +
 3 files changed, 29 insertions(+), 3 deletions(-)

diff --git a/scripts/Makefile.modpost b/scripts/Makefile.modpost
index 92ed02d7cd5e..c884b7b709ca 100644
--- a/scripts/Makefile.modpost
+++ b/scripts/Makefile.modpost
@@ -56,7 +56,8 @@ MODPOST = scripts/mod/modpost						\
 	$(if $(KBUILD_EXTMOD),$(addprefix -e ,$(KBUILD_EXTRA_SYMBOLS)))	\
 	$(if $(KBUILD_EXTMOD),-o $(modulesymfile))			\
 	$(if $(CONFIG_SECTION_MISMATCH_WARN_ONLY),,-E)			\
-	$(if $(KBUILD_MODPOST_WARN),-w)
+	$(if $(KBUILD_MODPOST_WARN),-w)					\
+	$(if $(CONFIG_LIVEPATCH),-l livepatch-modules)
 
 ifdef MODPOST_VMLINUX
 
diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
index 3e6d36ddfcdf..e3f637f225e4 100644
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -1976,6 +1976,10 @@ static void read_symbols(const char *modname)
 		license = get_next_modinfo(&info, "license", license);
 	}
 
+	/* Livepatch modules have unresolved symbols resolved by klp-convert */
+	if (get_modinfo(&info, "livepatch"))
+		mod->livepatch = 1;
+
 	for (sym = info.symtab_start; sym < info.symtab_stop; sym++) {
 		symname = remove_dot(info.strtab + sym->st_name);
 
@@ -2118,7 +2122,7 @@ static int check_exports(struct module *mod)
 		const char *basename;
 		exp = find_symbol(s->name);
 		if (!exp || exp->module == mod) {
-			if (have_vmlinux && !s->weak) {
+			if (have_vmlinux && !s->weak && !mod->livepatch) {
 				if (warn_unresolved) {
 					warn("\"%s\" [%s.ko] undefined!\n",
 					     s->name, mod->name);
@@ -2429,6 +2433,20 @@ static void write_dump(const char *fname)
 	free(buf.p);
 }
 
+static void write_livepatch_modules(const char *fname)
+{
+	struct buffer buf = { };
+	struct module *mod;
+
+	for (mod = modules; mod; mod = mod->next) {
+		if (mod->livepatch)
+			buf_printf(&buf, "%s\n", mod->name);
+	}
+
+	write_if_changed(&buf, fname);
+	free(buf.p);
+}
+
 struct ext_sym_list {
 	struct ext_sym_list *next;
 	const char *file;
@@ -2440,13 +2458,14 @@ int main(int argc, char **argv)
 	struct buffer buf = { };
 	char *kernel_read = NULL, *module_read = NULL;
 	char *dump_write = NULL, *files_source = NULL;
+	char *livepatch_modules = NULL;
 	int opt;
 	int err;
 	int n;
 	struct ext_sym_list *extsym_iter;
 	struct ext_sym_list *extsym_start = NULL;
 
-	while ((opt = getopt(argc, argv, "i:I:e:mnsT:o:awE")) != -1) {
+	while ((opt = getopt(argc, argv, "i:I:e:l:mnsT:o:awE")) != -1) {
 		switch (opt) {
 		case 'i':
 			kernel_read = optarg;
@@ -2463,6 +2482,9 @@ int main(int argc, char **argv)
 			extsym_iter->file = optarg;
 			extsym_start = extsym_iter;
 			break;
+		case 'l':
+			livepatch_modules = optarg;
+			break;
 		case 'm':
 			modversions = 1;
 			break;
@@ -2535,6 +2557,8 @@ int main(int argc, char **argv)
 	}
 	if (dump_write)
 		write_dump(dump_write);
+	if (livepatch_modules)
+		write_livepatch_modules(livepatch_modules);
 	if (sec_mismatch_count && sec_mismatch_fatal)
 		fatal("modpost: Section mismatches detected.\n"
 		      "Set CONFIG_SECTION_MISMATCH_WARN_ONLY=y to allow them.\n");
diff --git a/scripts/mod/modpost.h b/scripts/mod/modpost.h
index 8453d6ac2f77..2acfaae064ec 100644
--- a/scripts/mod/modpost.h
+++ b/scripts/mod/modpost.h
@@ -118,6 +118,7 @@ struct module {
 	int skip;
 	int has_init;
 	int has_cleanup;
+	int livepatch;
 	struct buffer dev_table_buf;
 	char	     srcversion[25];
 	int is_dot_o;
-- 
2.17.1