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Message-ID: <202005211441.F63205B7@keescook>
Date: Thu, 21 May 2020 14:54:39 -0700
From: Kees Cook <keescook@...omium.org>
To: Kristen Carlson Accardi <kristen@...ux.intel.com>
Cc: tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
arjan@...ux.intel.com, x86@...nel.org, linux-kernel@...r.kernel.org,
kernel-hardening@...ts.openwall.com, rick.p.edgecombe@...el.com
Subject: Re: [PATCH v2 0/9] Function Granular KASLR
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@...nel.org> on arm.
> * Fix build issue when building on arm as reported by
> Ard Biesheuvel <ardb@...nel.org>
> * 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
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