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Message-Id: <4D7F1590-2E77-4B29-BE6D-15CE41032287@digitalocean.com>
Date: Wed, 20 Nov 2019 10:19:10 -0600
From: Tianlin Li <tli@...italocean.com>
To: Borislav Petkov <bp@...en8.de>
Cc: kernel-hardening@...ts.openwall.com,
Kees Cook <keescook@...omium.org>,
Steven Rostedt <rostedt@...dmis.org>,
Ingo Molnar <mingo@...hat.com>,
Russell King <linux@...linux.org.uk>,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will@...nel.org>,
Greentime Hu <green.hu@...il.com>,
Vincent Chen <deanbo422@...il.com>,
Thomas Gleixner <tglx@...utronix.de>,
"H . Peter Anvin" <hpa@...or.com>,
x86@...nel.org,
Jessica Yu <jeyu@...nel.org>,
Josh Poimboeuf <jpoimboe@...hat.com>,
Jiri Kosina <jikos@...nel.org>,
Miroslav Benes <mbenes@...e.cz>,
Petr Mladek <pmladek@...e.com>,
Joe Lawrence <joe.lawrence@...hat.com>
Subject: Re: [RFC PATCH] kernel/module: have the callers of set_memory_*()
check the return value
> On Nov 20, 2019, at 3:58 AM, Borislav Petkov <bp@...en8.de> wrote:
>
> On Tue, Nov 19, 2019 at 09:51:49AM -0600, Tianlin Li wrote:
>> Right now several architectures allow their set_memory_*() family of
>> functions to fail, but callers may not be checking the return values. We
>> need to fix the callers and add the __must_check attribute.
>
> Please formulate commit messages in passive tone. "we" is ambiguous.
>
> From Documentation/process/submitting-patches.rst:
>
> "Describe your changes in imperative mood, e.g. "make xyzzy do frotz"
> instead of "[This patch] makes xyzzy do frotz" or "[I] changed xyzzy
> to do frotz", as if you are giving orders to the codebase to change
> its behaviour."
>
> Also, you could add a high-level summary of the failure case from:
>
> https://lore.kernel.org/netdev/20180628213459.28631-4-daniel@iogearbox.net/ <https://lore.kernel.org/netdev/20180628213459.28631-4-daniel@iogearbox.net/>
>
> as a more real-life, convincing justification for this.
Thanks for pointing it out. I will fix them in v2.
>> They also may not provide any level of atomicity, in the sense that
>> the memory protections may be left incomplete on failure.
>> This issue likely has a few
>> steps on effects architectures[1]:
>> 1)Have all callers of set_memory_*() helpers check the return value.
>> 2)Add __much_check to all set_memory_*() helpers so that new uses do not
>
> __must_check
>
>> ignore the return value.
>> 3)Add atomicity to the calls so that the memory protections aren't left in
>> a partial state.
>>
>> Ideally, the failure of set_memory_*() should be passed up the call stack,
>> and callers should examine the failure and deal with it. But currently,
>> some callers just have void return type.
>>
>> We need to fix the callers to handle the return all the way to the top of
>> stack, and it will require a large series of patches to finish all the three
>> steps mentioned above. I start with kernel/module, and will move onto other
>> subsystems. I am not entirely sure about the failure modes for each caller.
>> So I would like to get some comments before I move forward. This single
>> patch is just for fixing the return value of set_memory_*() function in
>> kernel/module, and also the related callers. Any feedback would be greatly
>> appreciated.
>>
>> [1]:https://github.com/KSPP/linux/issues/7
>>
>> Signed-off-by: Tianlin Li <tli@...italocean.com>
>> ---
>> arch/arm/kernel/ftrace.c | 8 +-
>> arch/arm64/kernel/ftrace.c | 6 +-
>> arch/nds32/kernel/ftrace.c | 6 +-
>> arch/x86/kernel/ftrace.c | 13 ++-
>> include/linux/module.h | 16 ++--
>> kernel/livepatch/core.c | 15 +++-
>> kernel/module.c | 170 +++++++++++++++++++++++++++----------
>> kernel/trace/ftrace.c | 15 +++-
>> 8 files changed, 175 insertions(+), 74 deletions(-)
>
> Yeah, general idea makes sense but you'd need to redo your patch ontop
> of linux-next because there are some changes in flight in ftrace-land at
> least and your patch won't apply anymore after next week, when the merge
> window opens.
>
> Also, you should use checkpatch before sending a patch as sometimes it makes
> sense what it complains about:
>
> WARNING: Missing a blank line after declarations
> #79: FILE: arch/arm/kernel/ftrace.c:68:
> + int ret;
> + ret = set_all_modules_text_ro();
>
> WARNING: Missing a blank line after declarations
> #150: FILE: arch/x86/kernel/ftrace.c:61:
> + int ret;
> + ret = set_all_modules_text_ro();
>
> WARNING: trailing semicolon indicates no statements, indent implies otherwise
> #203: FILE: kernel/livepatch/core.c:731:
> + if (module_enable_ro(patch->mod, true));
> + pr_err("module_enable_ro failed.\n");
>
> ERROR: trailing statements should be on next line
> #203: FILE: kernel/livepatch/core.c:731:
> + if (module_enable_ro(patch->mod, true));
>
> WARNING: Missing a blank line after declarations
> #451: FILE: kernel/module.c:2091:
> + int ret;
> + ret = frob_text(&mod->core_layout, set_memory_x);
>
> WARNING: Missing a blank line after declarations
> #511: FILE: kernel/trace/ftrace.c:5819:
> + int ret = ftrace_arch_code_modify_prepare();
> + if (ret) {
>
> WARNING: Missing a blank line after declarations
> #527: FILE: kernel/trace/ftrace.c:5864:
> + int ret = ftrace_arch_code_modify_post_process();
> + FTRACE_WARN_ON(ret);
>
>> diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
>> index c4ce08f43bd6..39bfc0685854 100644
>> --- a/kernel/livepatch/core.c
>> +++ b/kernel/livepatch/core.c
>> @@ -721,16 +721,25 @@ static int klp_init_object_loaded(struct klp_patch *patch,
>>
>> mutex_lock(&text_mutex);
>>
>> - module_disable_ro(patch->mod);
>> + ret = module_disable_ro(patch->mod);
>> + if (ret) {
>> + mutex_unlock(&text_mutex);
>> + return ret;
>> + }
>> ret = klp_write_object_relocations(patch->mod, obj);
>> if (ret) {
>> - module_enable_ro(patch->mod, true);
>> + if (module_enable_ro(patch->mod, true));
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>
> and if you look at its output above closely, it might even help you
> catch the bug you've added.
>
> [ Don't worry, happens to the best of us. :-) ]
>
> Also, what would help review is if you split your patch:
>
> patch 1: Change functions to return a retval
> patch 2-n: Change call sites to handle retval properly
ok. I will redo the patch on top of linux-next. I will use checkpatch and split the patch properly in v2.
Thanks for all valuable comments. Really appreciate it.
> Thx.
>
> --
> Regards/Gruss,
> Boris.
>
> https://people.kernel.org/tglx/notes-about-netiquette <https://people.kernel.org/tglx/notes-about-netiquette>
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