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Message-Id: <20190411202421.131779-1-joel@joelfernandes.org>
Date: Thu, 11 Apr 2019 16:24:21 -0400
From: "Joel Fernandes (Google)" <joel@...lfernandes.org>
To: linux-kernel@...r.kernel.org
Cc: "Joel Fernandes (Google)" <joel@...lfernandes.org>,
Rasmus Villemoes <linux@...musvillemoes.dk>,
paulmck@...ux.vnet.ibm.com,
rostedt@...dmis.org,
mathieu.desnoyers@...icios.com,
rcu@...r.kernel.org,
kernel-hardening@...ts.openwall.com,
kernel-team@...roid.com,
Josh Triplett <josh@...htriplett.org>,
Lai Jiangshan <jiangshanlai@...il.com>,
"Paul E. McKenney" <paulmck@...ux.ibm.com>
Subject: [PATCH] module: Make srcu_struct ptr array as read-only
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 <linux@...musvillemoes.dk>
Cc: paulmck@...ux.vnet.ibm.com
Cc: rostedt@...dmis.org
Cc: mathieu.desnoyers@...icios.com
Cc: rcu@...r.kernel.org
Cc: kernel-hardening@...ts.openwall.com
Cc: kernel-team@...roid.com
Signed-off-by: Joel Fernandes (Google) <joel@...lfernandes.org>
---
This single patch superceded the patches at: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
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