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Message-ID: <CALCETrXsQrVstLe4WAAWy-scMmS4Yxe95Lx05j3dmu41L76dMg@mail.gmail.com> Date: Wed, 7 Oct 2015 13:39:25 -0700 From: Andy Lutomirski <luto@...capital.net> To: Dave Hansen <dave@...1.net> Cc: Ingo Molnar <mingo@...nel.org>, X86 ML <x86@...nel.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "linux-mm@...ck.org" <linux-mm@...ck.org>, Linus Torvalds <torvalds@...ux-foundation.org>, Andrew Morton <akpm@...ux-foundation.org>, Peter Zijlstra <a.p.zijlstra@...llo.nl>, Andy Lutomirski <luto@...nel.org>, Borislav Petkov <bp@...en8.de>, Kees Cook <keescook@...gle.com>, Brian Gerst <brgerst@...il.com> Subject: Re: [PATCH 26/26] x86, pkeys: Documentation On Wed, Oct 7, 2015 at 1:24 PM, Dave Hansen <dave@...1.net> wrote: > On 10/03/2015 01:17 AM, Ingo Molnar wrote: >> Right now the native x86 PTE format allows two protection related bits for >> user-space pages: >> >> _PAGE_BIT_RW: if 0 the page is read-only, if 1 then it's read-write >> _PAGE_BIT_NX: if 0 the page is executable, if 1 then it's not executable >> >> As discussed previously, pkeys allows 'true execute only (--x)' mappings. >> >> Another possibility would be 'true write-only (-w-)' mappings. > > How would those work? > > Protection Keys has a Write-Disable and an Access-Disable bit. But, > Access-Disable denies _all_ data access to the region. There's no way > to allow only writes. Weird. I wonder why Intel did that. I also wonder whether EPT can do write-only. --Andy -- 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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