linux-kernel - Re: [RFC PATCH 2/3] module: Don't fail module loading when setting ro_after

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Message-ID: <a5622f46-5eb9-4c62-8a01-6f4bb0e3b701@csgroup.eu>
Date: Tue, 12 Nov 2024 12:08:03 +0100
From: Christophe Leroy <christophe.leroy@...roup.eu>
To: Daniel Gomez <da.gomez@...sung.com>, Luis Chamberlain
 <mcgrof@...nel.org>, Petr Pavlu <petr.pavlu@...e.com>,
 Sami Tolvanen <samitolvanen@...gle.com>, Kees Cook <kees@...nel.org>,
 linux-modules@...r.kernel.org
Cc: linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [RFC PATCH 2/3] module: Don't fail module loading when setting
 ro_after_init section RO failed



Le 12/11/2024 à 10:43, Daniel Gomez a écrit :
> On Mon Nov 11, 2024 at 7:53 PM CET, Christophe Leroy wrote:
>>
>>
>> Le 09/11/2024 à 23:17, Daniel Gomez a écrit :
>>> On Sat Nov 9, 2024 at 11:35 AM CET, Christophe Leroy wrote:
>>>> Once module init has succeded it is too late to cancel loading.
>>>> If setting ro_after_init data section to read-only fails, all we
>>>> can do is to inform the user through a warning.
>>>>
>>>> Reported-by: Thomas Gleixner <tglx@...utronix.de>
>>>> Closes: https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fprotect2.fireeye.com%2Fv1%2Furl%3Fk%3Dd3deb284-b2a35ac3-d3df39cb-74fe485fff30-288375d7d91e4ad9%26q%3D1%26e%3D701066ca-634d-4525-a77d-1a44451f897a%26u%3Dhttps%253A%252F%252Feur01.safelinks.protection.outlook.com%252F%253Furl%253Dhttps%25253A%25252F%25252Flore.kernel.org%25252Fall%25252F20230915082126.4187913-1-ruanjinjie%252540huawei.com%25252F%2526data%253D05%25257C02%25257Cchristophe.leroy%252540csgroup.eu%25257C26b5ca7363e54210439b08dd010c4865%25257C8b87af7d86474dc78df45f69a2011bb5%25257C0%25257C0%25257C638667874457200373%25257CUnknown%25257CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%25253D%25253D%25257C0%25257C%25257C%25257C%2526sdata%253DZeJ%25252F3%25252B2Nx%25252FBf%25252FWLFEkhxKlDhZk8LNkz0fs%25252Fg2xMcOjY%25253D%2526reserved%253D0&data=05%7C02%7Cchristophe.leroy%40csgroup.eu%7Cc86adbd7bad24b1042bd08dd02fe7c8e%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C638670014259822622%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=Gpxrx401fRdCGahGcI6GtJp%2BqLTZsnNqxsDoz4TAfU8%3D&reserved=0
>>>> Fixes: d1909c022173 ("module: Don't ignore errors from set_memory_XX()")
>>>> Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
>>>> ---
>>>>    kernel/module/main.c | 6 +++---
>>>>    1 file changed, 3 insertions(+), 3 deletions(-)
>>>>
>>>> diff --git a/kernel/module/main.c b/kernel/module/main.c
>>>> index 2de4ad7af335..1bf4b0db291b 100644
>>>> --- a/kernel/module/main.c
>>>> +++ b/kernel/module/main.c
>>>> @@ -2583,7 +2583,9 @@ static noinline int do_init_module(struct module *mod)
>>>>    #endif
>>>>    	ret = module_enable_rodata_ro_after_init(mod);
>>>>    	if (ret)
>>>> -		goto fail_mutex_unlock;
>>>> +		pr_warn("%s: %s() returned %d, ro_after_init data might still be writable\n",
>>>> +			mod->name, __func__, ret);
>>>> +
>>>>    	mod_tree_remove_init(mod);
>>>>    	module_arch_freeing_init(mod);
>>>>    	for_class_mod_mem_type(type, init) {
>>>> @@ -2622,8 +2624,6 @@ static noinline int do_init_module(struct module *mod)
>>>>    
>>>>    	return 0;
>>>
>>> I think it would make sense to propagate the error. But that would
>>> require changing modprobe.c. What kind of error can we expect when this
>>> happens?
>>
>> AFAIK, on powerpc it fails with EINVAL when
>> - The area is a vmalloc or module area and is a hugepage area
>> - The area is not vmalloc or io register and MMU is not powerpc radix MMU
>>
>> Otherwise it propagates the error from apply_to_existing_page_range().
>> IIUC it will return EINVAL when it hits a leaf PTE in upper directories.
> 
> Looking at that path I see we can also fail at __apply_to_page_range()
> -> apply_to_p4d_range() and return with -ENOMEM.

The -ENOMEM is when 'create' is true, usually when there is not enough 
memory available to create a page table ... in that case I guess you 
have much more problems to happen ...

set_memory_ro() on powerpc calls apply_to_existing_page_range() which 
implies 'create' is false.

Christophe