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Date: Wed, 17 Feb 2016 16:46:39 -0800 From: Andy Lutomirski <luto@...capital.net> To: Dave Hansen <dave@...1.net> Cc: Kees Cook <keescook@...gle.com>, Dave Hansen <dave.hansen@...ux.intel.com>, X86 ML <x86@...nel.org>, Linux-MM <linux-mm@...ck.org>, Andrew Morton <akpm@...ux-foundation.org>, LKML <linux-kernel@...r.kernel.org>, Linus Torvalds <torvalds@...ux-foundation.org> Subject: Re: [PATCH 33/33] x86, pkeys: execute-only support On Wed, Feb 17, 2016 at 2:53 PM, Dave Hansen <dave@...1.net> wrote: > On 02/17/2016 02:17 PM, Andy Lutomirski wrote: >>> > Is there a way to detect this feature's availability without userspace >>> > having to set up a segv handler and attempting to read a >>> > PROT_EXEC-only region? (i.e. cpu flag for protection keys, or a way to >>> > check the protection to see if PROT_READ got added automatically, >>> > etc?) >>> > >> We could add an HWCAP. > > I'll bite. What's an HWCAP? It's a CPU capability vector that's passed to every program as an auxv entry. On x86, ELF_HWCAP is useless (it's already fully used up for pointless purposes for CPUID stuff), but ELF_HWCAP2 could be added and a bit could be defined like HWCAP2_PROT_EXEC_ONLY. Some day, WRFSBASE, etc will be advertised via ELF_HWCAP2, I suspect. --Andy -- Andy Lutomirski AMA Capital Management, LLC
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