Re: [PATCH v4 15/16] module: Move where we mark modules RO,X

[Peter Zijlstra <peterz@infradead.org>]

On Mon, Oct 21, 2019 at 04:14:02PM +0200, Peter Zijlstra wrote:
> On Mon, Oct 21, 2019 at 08:53:12AM -0500, Josh Poimboeuf wrote:
> > On Fri, Oct 18, 2019 at 09:35:40AM +0200, Peter Zijlstra wrote:
> > > Now that set_all_modules_text_*() is gone, nothing depends on the
> > > relation between ->state = COMING and the protection state anymore.
> > > This enables moving the protection changes later, such that the COMING
> > > notifier callbacks can more easily modify the text.
> > > 
> > > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> > > Cc: Jessica Yu <jeyu@kernel.org>
> > > ---
> > >  kernel/module.c |    8 ++++----
> > >  1 file changed, 4 insertions(+), 4 deletions(-)
> > > 
> > > --- a/kernel/module.c
> > > +++ b/kernel/module.c
> > > @@ -3683,10 +3683,6 @@ static int complete_formation(struct mod
> > >  	/* This relies on module_mutex for list integrity. */
> > >  	module_bug_finalize(info->hdr, info->sechdrs, mod);
> > >  
> > > -	module_enable_ro(mod, false);
> > > -	module_enable_nx(mod);
> > > -	module_enable_x(mod);
> > > -
> > >  	/* Mark state as coming so strong_try_module_get() ignores us,
> > >  	 * but kallsyms etc. can see us. */
> > >  	mod->state = MODULE_STATE_COMING;
> > > @@ -3852,6 +3848,10 @@ static int load_module(struct load_info
> > >  	if (err)
> > >  		goto bug_cleanup;
> > >  
> > > +	module_enable_ro(mod, false);
> > > +	module_enable_nx(mod);
> > > +	module_enable_x(mod);
> > > +
> > >  	/* Module is ready to execute: parsing args may do that. */
> > >  	after_dashes = parse_args(mod->name, mod->args, mod->kp, mod->num_kp,
> > >  				  -32768, 32767, mod,
> > 
> > [ Sorry if this was already discussed, I still have a large backlog. ]
> > 
> > Doesn't livepatch code also need to be modified?  We have:
> 
> Urgh bah.. I was too focussed on the other klp borkage :/ But yes,
> arm64/ftrace and klp are the only two users of that function (outside of
> module.c) and Mark was already writing a patch for arm64.
> 
> Means these last two patches need to wait a little until we've fixed
> those.

So On IRC Josh suggested we use text_poke() for RELA. Since KLP is only
available on Power and x86, and Power does not have STRICT_MODULE_RWX,
the below should be sufficient.

Completely untested...

---
 arch/x86/kernel/module.c  | 40 +++++++++++++++++++++++++++++++++-------
 include/linux/livepatch.h |  7 +++++++
 kernel/livepatch/core.c   | 14 ++++++++++----
 3 files changed, 50 insertions(+), 11 deletions(-)

diff --git a/arch/x86/kernel/module.c b/arch/x86/kernel/module.c
index d5c72cb877b3..76fa2c5f2d7b 100644
--- a/arch/x86/kernel/module.c
+++ b/arch/x86/kernel/module.c
@@ -126,11 +126,12 @@ int apply_relocate(Elf32_Shdr *sechdrs,
 	return 0;
 }
 #else /*X86_64*/
-int apply_relocate_add(Elf64_Shdr *sechdrs,
+int __apply_relocate_add(Elf64_Shdr *sechdrs,
 		   const char *strtab,
 		   unsigned int symindex,
 		   unsigned int relsec,
-		   struct module *me)
+		   struct module *me,
+		   void *(*write)(void *addr, const void *val, size_t size))
 {
 	unsigned int i;
 	Elf64_Rela *rel = (void *)sechdrs[relsec].sh_addr;
@@ -162,19 +163,19 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
 		case R_X86_64_64:
 			if (*(u64 *)loc != 0)
 				goto invalid_relocation;
-			*(u64 *)loc = val;
+			write(loc, &val, 8);
 			break;
 		case R_X86_64_32:
 			if (*(u32 *)loc != 0)
 				goto invalid_relocation;
-			*(u32 *)loc = val;
+			write(loc, &val, 4);
 			if (val != *(u32 *)loc)
 				goto overflow;
 			break;
 		case R_X86_64_32S:
 			if (*(s32 *)loc != 0)
 				goto invalid_relocation;
-			*(s32 *)loc = val;
+			write(loc, &val, 4);
 			if ((s64)val != *(s32 *)loc)
 				goto overflow;
 			break;
@@ -183,7 +184,7 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
 			if (*(u32 *)loc != 0)
 				goto invalid_relocation;
 			val -= (u64)loc;
-			*(u32 *)loc = val;
+			write(loc, &val, 4);
 #if 0
 			if ((s64)val != *(s32 *)loc)
 				goto overflow;
@@ -193,7 +194,7 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
 			if (*(u64 *)loc != 0)
 				goto invalid_relocation;
 			val -= (u64)loc;
-			*(u64 *)loc = val;
+			write(loc, &val, 8);
 			break;
 		default:
 			pr_err("%s: Unknown rela relocation: %llu\n",
@@ -215,6 +216,31 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
 	       me->name);
 	return -ENOEXEC;
 }
+
+int apply_relocate_add(Elf64_Shdr *sechdrs,
+		   const char *strtab,
+		   unsigned int symindex,
+		   unsigned int relsec,
+		   struct module *me)
+{
+	return __apply_relocate_add(sechdrs, strtab, symindex, relsec, me, memcpy);
+}
+
+int klp_apply_relocate_add(Elf64_Shdr *sechdrs,
+		   const char *strtab,
+		   unsigned int symindex,
+		   unsigned int relsec,
+		   struct module *me)
+{
+	int ret;
+
+	ret = __apply_relocate_add(sechdrs, strtab, symindex, relsec, me, text_poke);
+	if (!ret)
+		text_poke_sync();
+
+	return ret;
+}
+
 #endif
 
 int module_finalize(const Elf_Ehdr *hdr,
diff --git a/include/linux/livepatch.h b/include/linux/livepatch.h
index 273400814020..5b8c10871b70 100644
--- a/include/linux/livepatch.h
+++ b/include/linux/livepatch.h
@@ -217,6 +217,13 @@ void *klp_shadow_get_or_alloc(void *obj, unsigned long id,
 void klp_shadow_free(void *obj, unsigned long id, klp_shadow_dtor_t dtor);
 void klp_shadow_free_all(unsigned long id, klp_shadow_dtor_t dtor);
 
+
+extern int klp_apply_relocate_add(Elf64_Shdr *sechdrs,
+			      const char *strtab,
+			      unsigned int symindex,
+			      unsigned int relsec,
+			      struct module *me);
+
 #else /* !CONFIG_LIVEPATCH */
 
 static inline int klp_module_coming(struct module *mod) { return 0; }
diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
index ab4a4606d19b..e690519aba31 100644
--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c
@@ -245,6 +245,15 @@ static int klp_resolve_symbols(Elf_Shdr *relasec, struct module *pmod)
 	return 0;
 }
 
+int __weak klp_apply_relocate_add(Elf64_Shdr *sechdrs,
+			      const char *strtab,
+			      unsigned int symindex,
+			      unsigned int relsec,
+			      struct module *me)
+{
+	apply_relocate_add(sechdrs, strtab, symindex, relsec, me);
+}
+
 static int klp_write_object_relocations(struct module *pmod,
 					struct klp_object *obj)
 {
@@ -285,7 +294,7 @@ static int klp_write_object_relocations(struct module *pmod,
 		if (ret)
 			break;
 
-		ret = apply_relocate_add(pmod->klp_info->sechdrs,
+		ret = klp_apply_relocate_add(pmod->klp_info->sechdrs,
 					 pmod->core_kallsyms.strtab,
 					 pmod->klp_info->symndx, i, pmod);
 		if (ret)
@@ -721,16 +730,13 @@ static int klp_init_object_loaded(struct klp_patch *patch,
 
 	mutex_lock(&text_mutex);
 
-	module_disable_ro(patch->mod);
 	ret = klp_write_object_relocations(patch->mod, obj);
 	if (ret) {
-		module_enable_ro(patch->mod, true);
 		mutex_unlock(&text_mutex);
 		return ret;
 	}
 
 	arch_klp_init_object_loaded(patch, obj);
-	module_enable_ro(patch->mod, true);
 
 	mutex_unlock(&text_mutex);