Messages in this thread | | | Date | Sat, 27 Jun 2020 18:12:14 -0400 | From | Steven Rostedt <> | Subject | Re: [PATCH] sched: fix build with GCC_PLUGIN_RANDSTRUCT |
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On Sat, 20 Jun 2020 13:41:36 +0300 Mike Rapoport <rppt@kernel.org> wrote:
> From: Mike Rapoport <rppt@linux.ibm.com> > > Since the commit a148866489fb ("sched: Replace rq::wake_list") > task_struct and CSD_TYPE_TTWU objects can be on the same queue and this > requires that have "layout similar enough". > > This assumption is broken when CONFIG_GCC_PLUGIN_RANDSTRUCT is enabled:
You forgot to Cc Kees, who's the one that is probably the most concerned about randomizing structures!
> > CHK include/generated/compile.h > CC kernel/smp.o > In file included from arch/x86/include/asm/atomic.h:5, > from include/linux/atomic.h:7, > from include/linux/llist.h:51, > from include/linux/irq_work.h:5, > from kernel/smp.c:10: > kernel/smp.c: In function ‘smp_init’: > include/linux/compiler.h:392:38: error: call to ‘__compiletime_assert_157’ declared with attribute error: BUILD_BUG_ON failed: offsetof(struct task_struct, wake_entry_type) - offsetof(struct task_struct, wake_entry) != offsetof(struct __call_single_data, flags) - offsetof(struct __call_single_data, llist) > 392 | _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__) > | ^ > include/linux/compiler.h:373:4: note: in definition of macro ‘__compiletime_assert’ > 373 | prefix ## suffix(); \ > | ^~~~~~ > include/linux/compiler.h:392:2: note: in expansion of macro ‘_compiletime_assert’ > 392 | _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__) > | ^~~~~~~~~~~~~~~~~~~ > include/linux/build_bug.h:39:37: note: in expansion of macro ‘compiletime_assert’ > 39 | #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg) > | ^~~~~~~~~~~~~~~~~~ > include/linux/build_bug.h:50:2: note: in expansion of macro ‘BUILD_BUG_ON_MSG’ > 50 | BUILD_BUG_ON_MSG(condition, "BUILD_BUG_ON failed: " #condition) > | ^~~~~~~~~~~~~~~~ > kernel/smp.c:687:2: note: in expansion of macro ‘BUILD_BUG_ON’ > 687 | BUILD_BUG_ON(offsetof(struct task_struct, wake_entry_type) - offsetof(struct task_struct, wake_entry) != > | ^~~~~~~~~~~~ > make[2]: *** [scripts/Makefile.build:280: kernel/smp.o] Error 1 > make[1]: *** [Makefile:1764: kernel] Error 2 > make[1]: *** Waiting for unfinished jobs.... > make[1]: Leaving directory '/home/mike/build/kernel' > make: *** [Makefile:185: __sub-make] Error 2
Seems the dependency is that the offsets between wake_entry and wake_entry_type doesn't change.
> > Move 'wake_entry' and 'wake_entry_type' fiels of task_struct out of > the randomized fields to keep their layout intact. > > Signed-off-by: Mike Rapoport <rppt@linux.ibm.com> > --- > include/linux/sched.h | 11 +++++++++-- > 1 file changed, 9 insertions(+), 2 deletions(-) > > diff --git a/include/linux/sched.h b/include/linux/sched.h > index b62e6aaf28f0..c885573669ac 100644 > --- a/include/linux/sched.h > +++ b/include/linux/sched.h > @@ -641,6 +641,15 @@ struct task_struct { > /* -1 unrunnable, 0 runnable, >0 stopped: */ > volatile long state; > > + /* > + * The layout of these fields must match the layout > CSD_TYPE_TTWU > + * so they can be on the same the @call_single_queue > + */ > +#ifdef CONFIG_SMP > + struct llist_node wake_entry; > + unsigned int wake_entry_type; > +#endif > + > /* > * This begins the randomizable portion of task_struct. Only > * scheduling-critical items should be added above here. > @@ -654,8 +663,6 @@ struct task_struct { > unsigned int ptrace; > > #ifdef CONFIG_SMP > - struct llist_node wake_entry; > - unsigned int wake_entry_type;
What about instead just create an anonymous structure of the two. That way they can still be randomized within the task struct and not be a target of attacks?
struct { struct llist_node wake_entry; unsigned int wake_entry_type; };
Would that work?
-- Steve
> int on_cpu; > #ifdef CONFIG_THREAD_INFO_IN_TASK > /* Current CPU: */
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