linux-kernel - Re: [PATCH v3 2/7] x86/jump_label: Use text_poke_early() during early

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Date:   Mon, 5 Nov 2018 21:28:29 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Andy Lutomirski <luto@...capital.net>
cc:     Nadav Amit <namit@...are.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andrew Lutomirski <luto@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Masami Hiramatsu <mhiramat@...nel.org>
Subject: Re: [PATCH v3 2/7] x86/jump_label: Use text_poke_early() during
 early_init

On Mon, 5 Nov 2018, Andy Lutomirski wrote:
> On Mon, Nov 5, 2018 at 11:25 AM Nadav Amit <namit@...are.com> wrote:
> Linus, hpa, or Dave, a question for you: suppose I map some page
> writably, write to it, then upgrade permissions to allow execute.
> Must I force all CPUs that might execute from it without first
> serializing to serialize?  I suspect this doesn't really affect user
> code, but it may affect the module loader.
> 
> To be safe, shouldn't the module loader broadcast an IPI to
> sync_core() everywhere after loading a module and before making it
> runnable, regardless of alternative patching?
> 
> IOW, the right sequence of events probably ought to me:
> 
> 1. Allocate the memory and map it.
> 2. Copy in the text.
> 3. Patch alternatives, etc.  This is logically just like (2) from an
> architectural perspective -- we're just writing to memory that won't
> be executed.
> 4. Serialize everything.
> 5. Run it!

I'd make that:

1. Allocate the memory and map it RW
2. Copy in the text.
3. Patch alternatives, etc.  This is logically just like (2) from an
   architectural perspective -- we're just writing to memory that won't
   be executed.
4. Map it RX
5. Serialize everything.
6. Run it!

Thanks,

	tglx