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

[Jessica Yu]

+++ 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@xxxxxxxxxx>
> > > Signed-off-by: Yang Yingliang <yangyingliang@xxxxxxxxxx>
> > > ---
> > > 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?
> OKïI 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.