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

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Date:   Tue, 18 Jun 2019 15:48:39 +0200
From:   Jessica Yu <jeyu@...nel.org>
To:     Yang Yingliang <yangyingliang@...wei.com>
Cc:     linux-kernel@...r.kernel.org, peterz@...radead.org,
        namit@...are.com, cj.chengjian@...wei.com
Subject: Re: [PATCH] modules: fix BUG when load module with rodata=n

+++ 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@...wei.com>
>Signed-off-by: Yang Yingliang <yangyingliang@...wei.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?

>@@ -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.

Thanks!

Jessica