On Thu, May 21, 2020 at 09:56:31AM -0700, Kristen Carlson Accardi wrote: > Changes in v2: > -------------- > * Fix to address i386 build failure > * Allow module reordering patch to be configured separately so that > arm (or other non-x86_64 arches) can take advantage of module function > reordering. This support has not be tested by me, but smoke tested by > Ard Biesheuvel <ardb@xxxxxxxxxx> on arm. > * Fix build issue when building on arm as reported by > Ard Biesheuvel <ardb@xxxxxxxxxx> > * minor chages for certain checkpatch warnings and review feedback. I successfully built and booted this on top of linux-next. For my builds I include: CONFIG_LOCK_DEBUGGING_SUPPORT=y CONFIG_PROVE_LOCKING=y CONFIG_DEBUG_RT_MUTEXES=y CONFIG_DEBUG_SPINLOCK=y CONFIG_DEBUG_MUTEXES=y CONFIG_DEBUG_WW_MUTEX_SLOWPATH=y CONFIG_DEBUG_RWSEMS=y CONFIG_DEBUG_LOCK_ALLOC=y CONFIG_LOCKDEP=y CONFIG_DEBUG_ATOMIC_SLEEP=y which catches various things. One of those (I assume either CONFIG_LOCKDEP or CONFIG_DEBUG_MUTEXES) has found an issue with kallsyms: [ 34.112989] ------------[ cut here ]------------ [ 34.113560] WARNING: CPU: 1 PID: 1997 at kernel/module.c:260 module_assert_mutex+0x29/0x30 [ 34.114479] Modules linked in: [ 34.114831] CPU: 1 PID: 1997 Comm: grep Tainted: G W 5.7.0-rc6-next-20200519+ #497 ... [ 34.128556] Call Trace: [ 34.128867] module_kallsyms_on_each_symbol+0x1d/0xa0 [ 34.130238] kallsyms_on_each_symbol+0xbd/0xd0 [ 34.131642] kallsyms_sorted_open+0x3f/0x70 [ 34.132160] proc_reg_open+0x99/0x180 [ 34.133222] do_dentry_open+0x176/0x400 [ 34.134182] vfs_open+0x2d/0x30 [ 34.134579] do_open.isra.0+0x2a0/0x410 [ 34.135058] path_openat+0x175/0x620 [ 34.135506] do_filp_open+0x91/0x100 [ 34.136912] do_sys_openat2+0x210/0x2d0 [ 34.137388] do_sys_open+0x46/0x80 [ 34.137818] __x64_sys_openat+0x20/0x30 [ 34.138288] do_syscall_64+0x55/0x1d0 [ 34.138720] entry_SYSCALL_64_after_hwframe+0x49/0xb3 Triggering it is easy, just "cat /proc/kallsyms" (and I'd note that I don't even have any modules loaded). Tracking this down, it just looks like kallsyms needs to hold a lock while sorting: diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c index 558963b275ec..182b16a6079b 100644 --- a/kernel/kallsyms.c +++ b/kernel/kallsyms.c @@ -772,7 +772,9 @@ static int kallsyms_sorted_open(struct inode *inode, struct file *file) INIT_LIST_HEAD(list); + mutex_lock(&module_mutex); ret = kallsyms_on_each_symbol(get_all_symbol_name, list); + mutex_unlock(&module_mutex); if (ret != 0) return ret; This fixes it for me. Everything else seems to be lovely. :) Nice work! -- Kees Cook
