Re: [PATCH v4 15/16] module: Move where we mark modules RO,X
From: Peter Zijlstra
Date: Mon Oct 21 2019 - 11:34:50 EST
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@xxxxxxxxxxxxx>
> > > Cc: Jessica Yu <jeyu@xxxxxxxxxx>
> > > ---
> > > 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);