Since commit title ("srcu: Allocate per-CPU data for DEFINE_SRCU() in
modules"), modules that call DEFINE_{STATIC,}SRCU will have a new array
of srcu_struct pointers, which is used by srcu code to initialize and
clean up these structures and save valuable per-cpu reserved space.
There is no reason for this array of pointers to be writable, and can
cause security or other hidden bugs. Mark these are read-only after the
module init has completed.
Tested with the following diff to ensure array not writable:
(diff is a bit reduced to avoid patch command getting confused)
a/kernel/module.c
b/kernel/module.c
-3506,6 +3506,14 static noinline int do_init_module [snip]
rcu_assign_pointer(mod->kallsyms, &mod->core_kallsyms);
#endif
module_enable_ro(mod, true);
+
+ if (mod->srcu_struct_ptrs) {
+ // Check if srcu_struct_ptrs access is possible
+ char x = *(char *)mod->srcu_struct_ptrs;
+ *(char *)mod->srcu_struct_ptrs = 0;
+ *(char *)mod->srcu_struct_ptrs = x;
+ }
+
mod_tree_remove_init(mod);
disable_ro_nx(&mod->init_layout);
module_arch_freeing_init(mod);
Cc: Rasmus Villemoes <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Signed-off-by: Joel Fernandes (Google) <[email protected]>
---
This single patch superceded the patches at:
https://lore.kernel.org/patchwork/patch/1060298/
https://lore.kernel.org/patchwork/patch/1060298/
include/linux/srcutree.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/include/linux/srcutree.h b/include/linux/srcutree.h
index 8af1824c46a8..9cfcc8a756ae 100644
--- a/include/linux/srcutree.h
+++ b/include/linux/srcutree.h
@@ -123,7 +123,7 @@ struct srcu_struct {
#ifdef MODULE
# define __DEFINE_SRCU(name, is_static) \
is_static struct srcu_struct name; \
- struct srcu_struct *__srcu_struct_##name \
+ struct srcu_struct * const __srcu_struct_##name \
__section("___srcu_struct_ptrs") = &name
#else
# define __DEFINE_SRCU(name, is_static) \
--
2.21.0.392.gf8f6787159e-goog
On Thu, Apr 11, 2019 at 04:24:21PM -0400, Joel Fernandes (Google) wrote:
> Since commit title ("srcu: Allocate per-CPU data for DEFINE_SRCU() in
> modules"), modules that call DEFINE_{STATIC,}SRCU will have a new array
> of srcu_struct pointers, which is used by srcu code to initialize and
> clean up these structures and save valuable per-cpu reserved space.
>
> There is no reason for this array of pointers to be writable, and can
> cause security or other hidden bugs. Mark these are read-only after the
> module init has completed.
>
> Tested with the following diff to ensure array not writable:
>
> (diff is a bit reduced to avoid patch command getting confused)
> a/kernel/module.c
> b/kernel/module.c
> -3506,6 +3506,14 static noinline int do_init_module [snip]
> rcu_assign_pointer(mod->kallsyms, &mod->core_kallsyms);
> #endif
> module_enable_ro(mod, true);
> +
> + if (mod->srcu_struct_ptrs) {
> + // Check if srcu_struct_ptrs access is possible
> + char x = *(char *)mod->srcu_struct_ptrs;
> + *(char *)mod->srcu_struct_ptrs = 0;
> + *(char *)mod->srcu_struct_ptrs = x;
> + }
> +
> mod_tree_remove_init(mod);
> disable_ro_nx(&mod->init_layout);
> module_arch_freeing_init(mod);
>
> Cc: Rasmus Villemoes <[email protected]>
> Cc: [email protected]
> Cc: [email protected]
> Cc: [email protected]
> Cc: [email protected]
> Cc: [email protected]
> Cc: [email protected]
> Signed-off-by: Joel Fernandes (Google) <[email protected]>
Queued for testing and further review, thank you, Joel!
Thanx, Paul
> ---
> This single patch superceded the patches at:
> https://lore.kernel.org/patchwork/patch/1060298/
> https://lore.kernel.org/patchwork/patch/1060298/
>
> include/linux/srcutree.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/linux/srcutree.h b/include/linux/srcutree.h
> index 8af1824c46a8..9cfcc8a756ae 100644
> --- a/include/linux/srcutree.h
> +++ b/include/linux/srcutree.h
> @@ -123,7 +123,7 @@ struct srcu_struct {
> #ifdef MODULE
> # define __DEFINE_SRCU(name, is_static) \
> is_static struct srcu_struct name; \
> - struct srcu_struct *__srcu_struct_##name \
> + struct srcu_struct * const __srcu_struct_##name \
> __section("___srcu_struct_ptrs") = &name
> #else
> # define __DEFINE_SRCU(name, is_static) \
> --
> 2.21.0.392.gf8f6787159e-goog
>
On Thu, Apr 11, 2019 at 02:31:55PM -0700, Paul E. McKenney wrote:
> On Thu, Apr 11, 2019 at 04:24:21PM -0400, Joel Fernandes (Google) wrote:
> > Since commit title ("srcu: Allocate per-CPU data for DEFINE_SRCU() in
> > modules"), modules that call DEFINE_{STATIC,}SRCU will have a new array
> > of srcu_struct pointers, which is used by srcu code to initialize and
> > clean up these structures and save valuable per-cpu reserved space.
> >
> > There is no reason for this array of pointers to be writable, and can
> > cause security or other hidden bugs. Mark these are read-only after the
> > module init has completed.
> >
> > Tested with the following diff to ensure array not writable:
> >
> > (diff is a bit reduced to avoid patch command getting confused)
> > a/kernel/module.c
> > b/kernel/module.c
> > -3506,6 +3506,14 static noinline int do_init_module [snip]
> > rcu_assign_pointer(mod->kallsyms, &mod->core_kallsyms);
> > #endif
> > module_enable_ro(mod, true);
> > +
> > + if (mod->srcu_struct_ptrs) {
> > + // Check if srcu_struct_ptrs access is possible
> > + char x = *(char *)mod->srcu_struct_ptrs;
> > + *(char *)mod->srcu_struct_ptrs = 0;
> > + *(char *)mod->srcu_struct_ptrs = x;
> > + }
> > +
> > mod_tree_remove_init(mod);
> > disable_ro_nx(&mod->init_layout);
> > module_arch_freeing_init(mod);
> >
> > Cc: Rasmus Villemoes <[email protected]>
> > Cc: [email protected]
> > Cc: [email protected]
> > Cc: [email protected]
> > Cc: [email protected]
> > Cc: [email protected]
> > Cc: [email protected]
> > Signed-off-by: Joel Fernandes (Google) <[email protected]>
>
> Queued for testing and further review, thank you, Joel!
Thanks a lot! I also just saw you added the rcutorture module to be built as
a part kselftests which is really cool ;-)
thanks,
- Joel
On Thu, Apr 11, 2019 at 10:14:22PM -0400, Joel Fernandes wrote:
> On Thu, Apr 11, 2019 at 02:31:55PM -0700, Paul E. McKenney wrote:
> > On Thu, Apr 11, 2019 at 04:24:21PM -0400, Joel Fernandes (Google) wrote:
> > > Since commit title ("srcu: Allocate per-CPU data for DEFINE_SRCU() in
> > > modules"), modules that call DEFINE_{STATIC,}SRCU will have a new array
> > > of srcu_struct pointers, which is used by srcu code to initialize and
> > > clean up these structures and save valuable per-cpu reserved space.
> > >
> > > There is no reason for this array of pointers to be writable, and can
> > > cause security or other hidden bugs. Mark these are read-only after the
> > > module init has completed.
> > >
> > > Tested with the following diff to ensure array not writable:
> > >
> > > (diff is a bit reduced to avoid patch command getting confused)
> > > a/kernel/module.c
> > > b/kernel/module.c
> > > -3506,6 +3506,14 static noinline int do_init_module [snip]
> > > rcu_assign_pointer(mod->kallsyms, &mod->core_kallsyms);
> > > #endif
> > > module_enable_ro(mod, true);
> > > +
> > > + if (mod->srcu_struct_ptrs) {
> > > + // Check if srcu_struct_ptrs access is possible
> > > + char x = *(char *)mod->srcu_struct_ptrs;
> > > + *(char *)mod->srcu_struct_ptrs = 0;
> > > + *(char *)mod->srcu_struct_ptrs = x;
> > > + }
> > > +
> > > mod_tree_remove_init(mod);
> > > disable_ro_nx(&mod->init_layout);
> > > module_arch_freeing_init(mod);
> > >
> > > Cc: Rasmus Villemoes <[email protected]>
> > > Cc: [email protected]
> > > Cc: [email protected]
> > > Cc: [email protected]
> > > Cc: [email protected]
> > > Cc: [email protected]
> > > Cc: [email protected]
> > > Signed-off-by: Joel Fernandes (Google) <[email protected]>
> >
> > Queued for testing and further review, thank you, Joel!
>
> Thanks a lot! I also just saw you added the rcutorture module to be built as
> a part kselftests which is really cool ;-)
Just a smoke test, really, but it will be interesting to see how
it goes. ;-)
Thanx, Paul