[PATCH v2 1/3] livepatch: Fix crash with !CONFIG_DEBUG_SET_MODULE_RONX

Josh Poimboeuf
2015-11-05T21:20:13Z

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: [<ffffffff8154fecb>] 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:[<ffffffff8154fecb>] [<ffffffff8154fecb>] 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] [<ffffffff810ecea9>] ? load_module+0x1e59/0x23a0
[ 205.990672] [<ffffffff810e8e40>] ? store_uevent+0x40/0x40
[ 205.990693] [<ffffffff810e99b5>] ? copy_module_from_fd.isra.49+0xb5/0x140
[ 205.990718] [<ffffffff810ed5bd>] ? SyS_finit_module+0x7d/0xa0
[ 205.990741] [<ffffffff81556832>] ? 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 <c7> 03 00 00 00 00 48 89 da 48 c7 c7 20 c7 a5 81 e8 d0 ec b3 ff
[ 205.990916] RIP [<ffffffff8154fecb>] do_init_module+0x8c/0x1ba
[ 205.990940] RSP <ffff8800794bbd58>
[ 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. <cbay@alwaysdata.com>
Tested-by: Cyril B. <cbay@alwaysdata.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
---
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

/* determine if the relocation spans a page boundary */
numpages = ((loc & PAGE_MASK) == ((loc + size) & PAGE_MASK)) ? 1 : 2;
--
2.4.3