Re: [PATCH] modules: fix BUG when load module with rodata=n

[Jessica Yu <jeyu@kernel.org>]

+++ Yang Yingliang [19/06/19 10:28 +0800]:
>
>
>On 2019/6/18 21:48, Jessica Yu wrote:
>>+++ Yang Yingliang [17/06/19 14:59 +0800]:
>>>When loading a module with rodata=n, it causes an executing
>>>NX-protected page BUG.
>>>
>>>[   32.379191] kernel tried to execute NX-protected page - exploit 
>>>attempt? (uid: 0)
>>>[   32.382917] BUG: unable to handle page fault for address: 
>>>ffffffffc0005000
>>>[   32.385947] #PF: supervisor instruction fetch in kernel mode
>>>[   32.387662] #PF: error_code(0x0011) - permissions violation
>>>[   32.389352] PGD 240c067 P4D 240c067 PUD 240e067 PMD 421a52067 
>>>PTE 8000000421a53063
>>>[   32.391396] Oops: 0011 [#1] SMP PTI
>>>[   32.392478] CPU: 7 PID: 2697 Comm: insmod Tainted: G           
>>>O      5.2.0-rc5+ #202
>>>[   32.394588] Hardware name: QEMU Standard PC (i440FX + PIIX, 
>>>1996), BIOS rel-1.12.1-0-ga5cab58e9a3f-prebuilt.qemu.org 
>>>04/01/2014
>>>[   32.398157] RIP: 0010:ko_test_init+0x0/0x1000 [ko_test]
>>>[   32.399662] Code: Bad RIP value.
>>>[   32.400621] RSP: 0018:ffffc900029f3ca8 EFLAGS: 00010246
>>>[   32.402171] RAX: 0000000000000000 RBX: 0000000000000000 RCX: 
>>>0000000000000000
>>>[   32.404332] RDX: 00000000000004c7 RSI: 0000000000000cc0 RDI: 
>>>ffffffffc0005000
>>>[   32.406347] RBP: ffffffffc0005000 R08: ffff88842fbebc40 R09: 
>>>ffffffff810ede4a
>>>[   32.408392] R10: ffffea00108e3480 R11: 0000000000000000 R12: 
>>>ffff88842bee21a0
>>>[   32.410472] R13: 0000000000000001 R14: 0000000000000001 R15: 
>>>ffffc900029f3e78
>>>[   32.412609] FS:  00007fb4f0c0a700(0000) 
>>>GS:ffff88842fbc0000(0000) knlGS:0000000000000000
>>>[   32.414722] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>>>[   32.416290] CR2: ffffffffc0004fd6 CR3: 0000000421a90004 CR4: 
>>>0000000000020ee0
>>>[   32.418471] Call Trace:
>>>[   32.419136]  do_one_initcall+0x41/0x1df
>>>[   32.420199]  ? _cond_resched+0x10/0x40
>>>[   32.421433]  ? kmem_cache_alloc_trace+0x36/0x160
>>>[   32.422827]  do_init_module+0x56/0x1f7
>>>[   32.423946]  load_module+0x1e67/0x2580
>>>[   32.424947]  ? __alloc_pages_nodemask+0x150/0x2c0
>>>[   32.426413]  ? map_vm_area+0x2d/0x40
>>>[   32.427530]  ? __vmalloc_node_range+0x1ef/0x260
>>>[   32.428850]  ? __do_sys_init_module+0x135/0x170
>>>[   32.430060]  ? _cond_resched+0x10/0x40
>>>[   32.431249]  __do_sys_init_module+0x135/0x170
>>>[   32.432547]  do_syscall_64+0x43/0x120
>>>[   32.433853]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
>>>
>>>Because if rodata=n, set_memory_x() cann't be called, fix this by
>>>calling set_memory_x in complete_formation();
>>>
>>>Fixes: f2c65fb3221a ("x86/modules: Avoid breaking W^X while 
>>>loading modules")
>>>Suggested-by: Jian Cheng <cj.chengjian@huawei.com>
>>>Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
>>>---
>>>kernel/module.c | 9 +++++++--
>>>1 file changed, 7 insertions(+), 2 deletions(-)
>>>
>>>diff --git a/kernel/module.c b/kernel/module.c
>>>index 80c7c09584cf..1a5d879573c3 100644
>>>--- a/kernel/module.c
>>>+++ b/kernel/module.c
>>>@@ -1949,12 +1949,10 @@ void module_enable_ro(const struct module 
>>>*mod, bool after_init)
>>>    set_vm_flush_reset_perms(mod->core_layout.base);
>>>    set_vm_flush_reset_perms(mod->init_layout.base);
>>>    frob_text(&mod->core_layout, set_memory_ro);
>>>-    frob_text(&mod->core_layout, set_memory_x);
>>>
>>>    frob_rodata(&mod->core_layout, set_memory_ro);
>>>
>>>    frob_text(&mod->init_layout, set_memory_ro);
>>>-    frob_text(&mod->init_layout, set_memory_x);
>>>
>>>    frob_rodata(&mod->init_layout, set_memory_ro);
>>
>>Just a style-related nit: could you also please shrink down this chunk
>>and remove the empty lines between the frob_* calls?
>OK，I will do it in next version.
>
>>
>>>@@ -2018,6 +2016,12 @@ void set_all_modules_text_ro(void)
>>>static void module_enable_nx(const struct module *mod) { }
>>>#endif
>>
>>And note that we will need a stub for module_enable_x() here as well.
>module_enable_x() is outside of CONFIG_STRICT_MODULE_RWX.

Ah yeah you're right, my mistake. We need it outside of the
CONFIG_STRICT_MODULE_RWX block anyway since module_alloc() on x86
allocates memory with PAGE_KERNEL now instead of PAGE_KERNEL_EXEC and
we need to set text to executable regardless.