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Date: Tue, 18 Jun 2019 16:28:12 +0200
From: Jessica Yu <jeyu@...nel.org>
To: Nadav Amit <namit@...are.com>
Cc: Yang Yingliang <yangyingliang@...wei.com>,
LKML <linux-kernel@...r.kernel.org>,
Peter Zijlstra <peterz@...radead.org>,
"cj.chengjian@...wei.com" <cj.chengjian@...wei.com>,
Borislav Petkov <bp@...en8.de>
Subject: Re: [PATCH] modules: fix BUG when load module with rodata=n
+++ Nadav Amit [18/06/19 05:59 +0000]:
>> On Jun 16, 2019, at 11:59 PM, Yang Yingliang <yangyingliang@...wei.com> wrote:
>>
>> 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);
>>
>> @@ -2018,6 +2016,12 @@ void set_all_modules_text_ro(void)
>> static void module_enable_nx(const struct module *mod) { }
>> #endif
>>
>> +static void module_enable_x(const struct module *mod)
>> +{
>> + frob_text(&mod->core_layout, set_memory_x);
>> + frob_text(&mod->init_layout, set_memory_x);
>> +}
>> +
>> #ifdef CONFIG_LIVEPATCH
>> /*
>> * Persist Elf information about a module. Copy the Elf header,
>> @@ -3616,6 +3620,7 @@ static int complete_formation(struct module *mod, struct load_info *info)
>>
>> module_enable_ro(mod, false);
>> module_enable_nx(mod);
>> + module_enable_x(mod);
>>
>> /* Mark state as coming so strong_try_module_get() ignores us,
>> * but kallsyms etc. can see us. */
>> --
>> 2.17.1
>
>It does seem that I screwed up (thanks for fixing it!).
>
>Makes me wonder why module_enable_ro() is needed to be called twice
>(excluding the write-protecting of the core_layout). I wonder since this
>patch would eliminate some calls to set_memory_x(), which indeed do not seem
>necessary.
>
>Skimming 444d13ff10fb1 ("modules: add ro_after_init support”), I could
>not understand why.
>
>Anyhow,
>
>Reviewed-by: Nadav Amit <namit@...are.com>
Indeed, you're right that the second module_enable_ro() call is mostly
redundant. It is for adding RO protection to the ro_after_init
section, but I believe the reason for redundancy was that we wanted to
re-use the function for livepatching, as livepatch calls
module_disable_ro() and module_enable_ro() to apply relocations.
Since module_enable_ro() was being called outside of the module
loader, we needed to make sure all RO protections were applied again,
including the ro_after_init section. I'll have to think about this
more to see if we can remove the redundancy without making the
module_enable_ro()/module_disable_ro() api too messy..
Thanks,
Jessica
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