Date: Thu, 7 Mar 2019 18:06:29 +0100 From: Borislav Petkov <bp@...en8.de> To: hpa@...or.com Cc: Nadav Amit <nadav.amit@...il.com>, Rick Edgecombe <rick.p.edgecombe@...el.com>, Andy Lutomirski <luto@...nel.org>, Ingo Molnar <mingo@...hat.com>, LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>, Thomas Gleixner <tglx@...utronix.de>, Dave Hansen <dave.hansen@...ux.intel.com>, Peter Zijlstra <peterz@...radead.org>, Damian Tometzki <linux_dti@...oud.com>, linux-integrity <linux-integrity@...r.kernel.org>, LSM List <linux-security-module@...r.kernel.org>, Andrew Morton <akpm@...ux-foundation.org>, Kernel Hardening <kernel-hardening@...ts.openwall.com>, Linux-MM <linux-mm@...ck.org>, Will Deacon <will.deacon@....com>, Ard Biesheuvel <ard.biesheuvel@...aro.org>, Kristen Carlson Accardi <kristen@...ux.intel.com>, "Dock, Deneen T" <deneen.t.dock@...el.com>, Kees Cook <keescook@...omium.org>, Dave Hansen <dave.hansen@...el.com>, Masami Hiramatsu <mhiramat@...nel.org> Subject: Re: [PATCH v2 10/20] x86: avoid W^X being broken during modules loading On Thu, Mar 07, 2019 at 08:53:34AM -0800, hpa@...or.com wrote: > If we *do*, what is the issue here? Although boot_cpu_has() isn't > slow (it should in general be possible to reduce to one testb > instruction followed by a conditional jump) it seems that "avoiding an > alternatives slot" *should* be a *very* weak reason, and seems to me > to look like papering over some other problem. Forget the current thread: this is simply trying to document when to use static_cpu_has() and when to use boot_cpu_has(). I get asked about it at least once a month. And then it is replacing clear slow paths using static_cpu_has() with boot_cpu_has() because there's purely no need to patch there. And having a RIP-relative MOV and a JMP is good enough for slow paths. Makes sense? -- Regards/Gruss, Boris. Good mailing practices for 400: avoid top-posting and trim the reply.
Powered by blists - more mailing lists
Confused about mailing lists and their use? Read about mailing lists on Wikipedia and check out these guidelines on proper formatting of your messages.