Messages in this thread | | | Date | Mon, 24 Oct 2022 09:14:45 -0700 | Subject | Re: [PATCH] x86/mm: Do not verify W^X at boot up | From | Dave Hansen <> |
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On 10/24/22 08:45, Steven Rostedt wrote: > --- a/arch/x86/mm/pat/set_memory.c > +++ b/arch/x86/mm/pat/set_memory.c > @@ -587,6 +587,10 @@ static inline pgprot_t verify_rwx(pgprot_t old, pgprot_t new, unsigned long star > { > unsigned long end; > > + /* Kernel text is rw at boot up */ > + if (system_state == SYSTEM_BOOTING) > + return new;
Hi Steven,
Thanks for the report and the patch. That seems reasonable, but I'm a bit worried that it opens up a big hole (boot time) when a W+X mapping could be created *anywhere*.
Could we restrict this bypass to *only* kernel text addresses during boot? Maybe something like this:
if ((system_state == SYSTEM_BOOTING) && __kernel_text_address(start)) return new;
That would be safe because we know that kernel_text_address() addresses will be made read-only by the time userspace shows up and that is_kernel_inittext() addresses will be freed.
Long-term, I wonder if we could teach the early patching code that it can't just use memcpy().
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