Messages in this thread | | | From | Vlastimil Babka <> | Subject | Re: [PATCH 3/3] [v4] lib/vsprintf: no_hash_pointers prints all addresses as unhashed | Date | Tue, 2 Mar 2021 14:37:19 +0100 |
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On 3/2/21 2:29 PM, Petr Mladek wrote: > On Tue 2021-03-02 13:51:35, Geert Uytterhoeven wrote: >> > > > + >> > > > + pr_warn("**********************************************************\n"); >> > > > + pr_warn("** NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE **\n"); >> > > > + pr_warn("** **\n"); >> > > > + pr_warn("** This system shows unhashed kernel memory addresses **\n"); >> > > > + pr_warn("** via the console, logs, and other interfaces. This **\n"); >> > > > + pr_warn("** might reduce the security of your system. **\n"); >> > > > + pr_warn("** **\n"); >> > > > + pr_warn("** If you see this message and you are not debugging **\n"); >> > > > + pr_warn("** the kernel, report this immediately to your system **\n"); >> > > > + pr_warn("** administrator! **\n"); >> > > > + pr_warn("** **\n"); >> > > > + pr_warn("** NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE **\n"); >> > > > + pr_warn("**********************************************************\n"); >> > > > + >> > > > + return 0; >> > > > +} >> > > > +early_param("no_hash_pointers", no_hash_pointers_enable); >> > > >> > > While bloat-o-meter is not smart enough to notice the real size impact, >> > > this does add more than 500 bytes of string data to the kernel. >> > > Do we really need such a large message? >> > > Perhaps the whole no_hash_pointers machinery should be protected by >> > > "#ifdef CONFIG_DEBUG_KERNEL"? > > This was the deal. The configure option is a no-go, see below and also > https://lore.kernel.org/r/CAHk-=wgaK4cz=K-JB4p-KPXBV73m9bja2w1W1Lr3iu8+NEPk7A@mail.gmail.com
I think it's a no-go only when enabling such option equals to "no_hash_pointers" being always passed. What Geert suggests is that you need both CONFIG_DEBUG_KERNEL *and* no_hash_pointers and that's different.
>> > We recently stumbled across this, and it appears an increasing number >> > of production kernels enable CONFIG_DEBUG_KERNEL [1], so it likely >> > isn't the solution (we tried to use CONFIG_DEBUG_KERNEL in similar >> >> I guess the people who do care about kernel size do know to disable >> CONFIG_DEBUG_KERNEL, so it would help them. >> The everything-but-the-kitchen-sink distro people don't care about kernel >> size anyway. > > The problem with the configure option is not about size. The problem is > that there would be many kernels in the wild with this option enabled. > People would install them without knowing that they are less secure.
Same as above.
> Distros would need to provide both kernels. Well, they already do. > But it might be worse. Some distros might even want to enable it > by default. > > Also many bugs might be debugged without this option. Some bugs > are hard to reproduce and might be visible only on production > systems. It should be possible to enable this only when really > needed and the user must be aware of the risk.
So this is basically a kernel tinyfication issue, right? Is that still pursued today? Are there better config options suitable for this than CONFIG_DEBUG_KERNEL?
>> > Would placing the strings into an __initconst array help? >> >> That would indeed help to reduce run-time memory consumption. > > Sure. We could do this. Do you want to send a patch, please? > >> It would not solve the raw kernel size increase. > > I see. Well, the compression should be pretty efficient > for a text (with many spaces). > > Best Regards, > Petr >
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