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SubjectRe: [PATCH] modules: fix BUG when load module with rodata=n
+++ 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.




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