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SubjectRe: [PATCH v3 5/6] x86/ftrace: Use text_poke()
On Wed, Oct 16, 2019 at 08:51:27AM +0200, Miroslav Benes wrote:
> On Tue, 15 Oct 2019, Joe Lawrence wrote:
>
> > On 10/15/19 10:13 AM, Miroslav Benes wrote:
> > > Yes, it does. klp_module_coming() calls module_disable_ro() on all
> > > patching modules which patch the coming module in order to call
> > > apply_relocate_add(). New (patching) code for a module can be relocated
> > > only when the relevant module is loaded.
> >
> > FWIW, would the LPC blue-sky2 model (ie, Steve's suggestion @ plumber's where
> > livepatches only patch a single object and updates are kept on disk to handle
> > coming module updates as they are loaded) eliminate those outstanding
> > relocations and the need to perform this late permission flipping?
>
> Yes, it should, but we don't have to wait for it. PeterZ proposed a
> different solution to this specific issue in
> https://lore.kernel.org/lkml/20191015141111.GP2359@hirez.programming.kicks-ass.net/
>
> It should not be a problem to create a live patch module like that and the
> code in kernel/livepatch/ is almost ready. Something like
> module_section_disable_ro(mod, section) (and similar for X protection)
> should be enough. Module reloads would still require juggling with the
> protections, but I think it is all feasible.

Something a little like so.. completely fresh of the keyboard.

---
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -853,6 +853,18 @@ static inline void module_enable_ro(cons
static inline void module_disable_ro(const struct module *mod) { }
#endif

+#if defined(CONFIG_STRICT_MODULE_RWX) && defined(CONFIG_LIVEPATCH)
+extern void module_section_disable_ro(struct module *mod, const char *sec);
+extern void module_section_enable_ro(struct module *mod, const char *sec);
+extern void module_section_disable_x(struct module *mod, const char *sec);
+extern void module_section_enable_x(struct module *mod, const char *sec);
+#else
+static inline void module_section_disable_ro(struct module *mod, const char *sec) { }
+static inline void module_section_enable_ro(struct module *mod, const char *sec) { }
+static inline void module_section_disable_x(struct module *mod, const char *sec) { }
+static inline void module_section_enable_x(struct module *mod, const char *sec) { }
+#endif
+
#ifdef CONFIG_GENERIC_BUG
void module_bug_finalize(const Elf_Ehdr *, const Elf_Shdr *,
struct module *);
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -2107,6 +2107,54 @@ static void free_module_elf(struct modul
kfree(mod->klp_info->secstrings);
kfree(mod->klp_info);
}
+
+#ifdef CONFIG_STRICT_MODULE_RWX
+
+static void __frob_section(struct Elf_Shdr *sec, int (*set_memory)(unsigned long start, int num_pages))
+{
+ BUG_ON((unsigned long)sec->sh_addr & (PAGE_SIZE-1));
+ BUG_ON((unsigned long)sec->sh_size & (PAGE_SIZE-1));
+ set_memory((unsigned long)sec->sh_addr, sec->sh_size >> PAGE_SHIFT);
+}
+
+static void frob_section(struct module *mod, const char *section,
+ int (*set_memory)(unsigned long start, int num_pages))
+{
+ struct klp_modinfo *info = mod->klp_info;
+ const char *secname;
+ Elf_Shdr *s;
+
+ for (s = info->sechdrs; s < info->sechdrs + info->hdr.e_shnum; s++) {
+ secname = mod->klp_info->secstrings + s->sh_name;
+ if (strcmp(secname, section))
+ continue;
+
+ __frob_section(s, set_memory);
+ }
+}
+
+void module_section_disable_ro(struct module *mod, const char *section)
+{
+ frob_section(mod, section, set_memory_rw);
+}
+
+void module_section_enable_ro(struct module *mod, const char *section)
+{
+ frob_section(mod, section, set_memory_ro);
+}
+
+void module_section_disable_x(struct module *mod, const char *section)
+{
+ frob_section(mod, section, set_memory_nx);
+}
+
+void module_section_enable_x(struct module *mod, const char *section)
+{
+ frob_section(mod, section, set_memory_x);
+}
+
+#endif /* ONFIG_STRICT_MODULE_RWX */
+
#else /* !CONFIG_LIVEPATCH */
static int copy_module_elf(struct module *mod, struct load_info *info)
{
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