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Message-ID: <CA+55aFxf3ExQEq2zhNhj4zk5nC5in9=1acVfynOVxZdN9RLbdA@mail.gmail.com> Date: Thu, 1 Oct 2015 21:38:10 -0400 From: Linus Torvalds <torvalds@...ux-foundation.org> To: Dave Hansen <dave@...1.net> Cc: Kees Cook <keescook@...gle.com>, Ingo Molnar <mingo@...nel.org>, "x86@...nel.org" <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>, Linux-MM <linux-mm@...ck.org>, Andrew Morton <akpm@...ux-foundation.org>, Peter Zijlstra <a.p.zijlstra@...llo.nl>, Andy Lutomirski <luto@...nel.org>, Borislav Petkov <bp@...en8.de> Subject: Re: [PATCH 26/26] x86, pkeys: Documentation On Thu, Oct 1, 2015 at 6:56 PM, Dave Hansen <dave@...1.net> wrote: > > Also, a quick ftrace showed that most mmap() callers that set PROT_EXEC > also set PROT_READ. I'm just assuming that folks are setting PROT_READ > but aren't _really_ going to read it, so we can safely deny them all > access other than exec. That's a completely insane assumption. There are tons of reasons to have code and read-only data in the same segment, and it's very traditional. Just assuming that you only execute out of something that has PROT_EXEC | PROT_READ is insane. No, what you *should* look at is to use the protection keys to actually enforce a plain PROT_EXEC. That has never worked before (because traditionally R implies X, and then we got NX). That would at least allow people who know they don't intersperse read-only constants in the code to use PROT_EXE only. Of course, there may well be users who use PROT_EXE that actually *do* do reads, and just relied on the old hardware behavior. So it's not guaranteed to work either without any extra flags. But at least it's worth a try, unlike the "yeah, the user asked for read, but the user doesn't know what he's doing" thinking that is just crazy talk. Linus -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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