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Date: Wed, 20 Nov 2019 10:58:04 +0100
From: Borislav Petkov <bp@...en8.de>
To: Tianlin Li <tli@...italocean.com>
Cc: kernel-hardening@...ts.openwall.com, 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 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/
as a more real-life, convincing justification for this.
> 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
Thx.
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
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