From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Thu, 11 Apr 2019 22:14:22 -0400 From: Joel Fernandes Subject: Re: [PATCH] module: Make srcu_struct ptr array as read-only Message-ID: <20190412021422.GA208673@google.com> References: <20190411202421.131779-1-joel@joelfernandes.org> <20190411213155.GD14111@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190411213155.GD14111@linux.ibm.com> To: "Paul E. McKenney" Cc: linux-kernel@vger.kernel.org, Rasmus Villemoes , rostedt@goodmis.org, mathieu.desnoyers@efficios.com, rcu@vger.kernel.org, kernel-hardening@lists.openwall.com, kernel-team@android.com, Josh Triplett , Lai Jiangshan List-ID: 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 > > Cc: paulmck@linux.vnet.ibm.com > > Cc: rostedt@goodmis.org > > Cc: mathieu.desnoyers@efficios.com > > Cc: rcu@vger.kernel.org > > Cc: kernel-hardening@lists.openwall.com > > Cc: kernel-team@android.com > > Signed-off-by: Joel Fernandes (Google) > > 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