From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755357AbbKCPW4 (ORCPT ); Tue, 3 Nov 2015 10:22:56 -0500 Received: from mx1.redhat.com ([209.132.183.28]:37031 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754588AbbKCPWv (ORCPT ); Tue, 3 Nov 2015 10:22:51 -0500 Date: Tue, 3 Nov 2015 09:22:49 -0600 From: Josh Poimboeuf To: Miroslav Benes Cc: Seth Jennings , Jiri Kosina , Vojtech Pavlik , linux-kernel@vger.kernel.org, live-patching@vger.kernel.org, "Cyril B." Subject: Re: [PATCH] x86/livepatch: Fix crash with !CONFIG_DEBUG_SET_MODULE_RONX Message-ID: <20151103152249.GL27488@treble.redhat.com> References: <132b018cfe2c6e4cef4d1b62ac3ed70333734111.1446494413.git.jpoimboe@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23.1-rc1 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Nov 03, 2015 at 11:22:12AM +0100, Miroslav Benes wrote: > On Mon, 2 Nov 2015, Josh Poimboeuf wrote: > > > When loading a patch module on a kernel with > > !CONFIG_DEBUG_SET_MODULE_RONX, the following crash occurs: > > > > [ 205.988776] livepatch: enabling patch 'kpatch_meminfo_string' > > [ 205.989829] BUG: unable to handle kernel paging request at ffffffffa08d2fc0 > > [ 205.989863] IP: [] do_init_module+0x8c/0x1ba > > [ 205.989888] PGD 1a10067 PUD 1a11063 PMD 7bcde067 PTE 3740e161 > > [ 205.989915] Oops: 0003 [#1] SMP > > [ 205.990187] CPU: 2 PID: 14570 Comm: insmod Tainted: G O K 4.1.12 > > [ 205.990214] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.8.1-20150318_183358- 04/01/2014 > > [ 205.990249] task: ffff8800374aaa90 ti: ffff8800794b8000 task.ti: ffff8800794b8000 > > [ 205.990276] RIP: 0010:[] [] do_init_module+0x8c/0x1ba > > [ 205.990307] RSP: 0018:ffff8800794bbd58 EFLAGS: 00010246 > > [ 205.990327] RAX: 0000000000000000 RBX: ffffffffa08d2fc0 RCX: 0000000000000000 > > [ 205.990356] RDX: 01ffff8000000080 RSI: 0000000000000000 RDI: ffffffff81a54b40 > > [ 205.990382] RBP: ffff88007b4c4d80 R08: 0000000000000007 R09: 0000000000000000 > > [ 205.990408] R10: 0000000000000008 R11: ffffea0001f18840 R12: 0000000000000000 > > [ 205.990433] R13: 0000000000000001 R14: ffffffffa08d2fc0 R15: ffff88007bd0bc40 > > [ 205.990459] FS: 00007f1128fbc700(0000) GS:ffff88007fc80000(0000) knlGS:0000000000000000 > > [ 205.990488] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > > [ 205.990509] CR2: ffffffffa08d2fc0 CR3: 000000002606e000 CR4: 00000000001406e0 > > [ 205.990536] Stack: > > [ 205.990545] ffff8800794bbec8 0000000000000001 ffffffffa08d3010 ffffffff810ecea9 > > [ 205.990576] ffffffff810e8e40 000000000005f360 ffff88007bd0bc50 ffffffffa08d3240 > > [ 205.990608] ffffffffa08d52c0 ffffffffa08d3210 ffff8800794bbed8 ffff8800794bbf1c > > [ 205.990639] Call Trace: > > [ 205.990651] [] ? load_module+0x1e59/0x23a0 > > [ 205.990672] [] ? store_uevent+0x40/0x40 > > [ 205.990693] [] ? copy_module_from_fd.isra.49+0xb5/0x140 > > [ 205.990718] [] ? SyS_finit_module+0x7d/0xa0 > > [ 205.990741] [] ? system_call_fastpath+0x16/0x75 > > [ 205.990763] Code: f9 00 00 00 74 23 49 c7 c0 92 e1 60 81 48 8d 53 18 89 c1 4c 89 c6 48 c7 c7 f0 85 7d 81 31 c0 e8 71 fa ff ff e8 58 0e 00 00 31 f6 03 00 00 00 00 48 89 da 48 c7 c7 20 c7 a5 81 e8 d0 ec b3 ff > > [ 205.990916] RIP [] do_init_module+0x8c/0x1ba > > [ 205.990940] RSP > > [ 205.990953] CR2: ffffffffa08d2fc0 > > > > With !CONFIG_DEBUG_SET_MODULE_RONX, module text and rodata pages are > > writable, and the debug_align() macro allows the module struct to share > > a page with executable text. When klp_write_module_reloc() calls > > set_memory_ro() on the page, it effectively turns the module struct into > > a read-only structure, resulting in a page fault when load_module() does > > "mod->state = MODULE_STATE_LIVE". > > > > Reported-by: Cyril B. > > Tested-by: Cyril B. > > Signed-off-by: Josh Poimboeuf > > --- > > Oh, this reminds me I had to solve this issue in kgraft while playing with > relocations. I wanted to fix it in klp as well and forgot about it so it > is great to see it done. > > Anyway... > > > arch/x86/kernel/livepatch.c | 9 +++++---- > > 1 file changed, 5 insertions(+), 4 deletions(-) > > > > diff --git a/arch/x86/kernel/livepatch.c b/arch/x86/kernel/livepatch.c > > index ff3c3101d..d1d35cc 100644 > > --- a/arch/x86/kernel/livepatch.c > > +++ b/arch/x86/kernel/livepatch.c > > @@ -42,7 +42,6 @@ int klp_write_module_reloc(struct module *mod, unsigned long type, > > bool readonly; > > unsigned long val; > > unsigned long core = (unsigned long)mod->module_core; > > - unsigned long core_ro_size = mod->core_ro_size; > > unsigned long core_size = mod->core_size; > > > > switch (type) { > > @@ -70,10 +69,12 @@ int klp_write_module_reloc(struct module *mod, unsigned long type, > > /* loc does not point to any symbol inside the module */ > > return -EINVAL; > > > > - if (loc < core + core_ro_size) > > + readonly = false; > > + > > +#ifdef CONFIG_DEBUG_SET_MODULE_RONX > > + if (loc < core + mod->core_ro_size) > > readonly = true; > > - else > > - readonly = false; > > +#endif > > > > Wouldn't it be better to use static inline function defined somewhere in > our header file which would do the job for CONFIG_DEBUG_SET_MODULE_RONX > set and nothing for the opposite? I think it is better than to have ifdef > here. Probably just a matter of taste. I agree that would be better. Though I think I'd make a static function in the .c file so it stays internal. > Secondly, why do we call set_memory_rw/ro here for each relocation? > Wouldn't it be possible to do it once for all the relevant pages of the > patched module? I mean we could call set_memory_rw in > klp_write_object_relocations from kernel/livepatch/core.c just before the > for loop and set_memory_ro on the way out. With the static inline function > it could look like this > > +#ifdef CONFIG_DEBUG_SET_MODULE_RONX > +static inline void set_module_text(void *start, void *end, int (*set)(unsigned long start, > + int num_pages)) > +{ > + unsigned long begin_pfn = PFN_DOWN((unsigned long)start); > + unsigned long end_pfn = PFN_DOWN((unsigned long)end); > + > + if (end_pfn > begin_pfn) > + set(begin_pfn << PAGE_SHIFT, end_pfn - begin_pfn); > +} > +#else > +static inline void set_module_text(void *start, void *end, int (*set)(unsigned long start, > + int num_pages)) { } > +#endif > > somewhere in include/linux/livepatch.h. And in > klp_write_object_relocations() there could be > > + set_module_text(mod->module_core, mod->module_core + > + mod->core_text_size, set_memory_rw); > > just before the for loop which goes through all the relocations > > and > > + set_module_text(mod->module_core, mod->module_core + > + mod->core_text_size, set_memory_ro); > > on the way out. > > We would also get rid of readonly variable. > > At least this is how I solved it. Take it as an idea. I don't know if it > is even better and I certainly do not insist on it. Your approach is ok. Yeah, I like this idea. Though we have to be careful. Not only can relocations occur in text, they can also occur in data. So we'd have to set read-only data writable as well. So it should be "mod->module_core + mod->core_ro_size". -- Josh