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From: Kees Cook <keescook@google.com>
To: Dave Hansen <dave@sr71.net>
Cc: LKML <linux-kernel@vger.kernel.org>,
	Linux-MM <linux-mm@kvack.org>, "x86@kernel.org" <x86@kernel.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Andy Lutomirski <luto@amacapital.net>
Subject: Re: [PATCH 33/33] x86, pkeys: execute-only support
Date: Wed, 17 Feb 2016 13:36:15 -0800	[thread overview]
Message-ID: <CAGXu5jJyLHTHn4Los2KJ-Hy5zfOUsavTs74ba4-81eTeXEgc_w@mail.gmail.com> (raw)
In-Reply-To: <56C4E720.4050800@sr71.net>

On Wed, Feb 17, 2016 at 1:33 PM, Dave Hansen <dave@sr71.net> wrote:
> On 02/17/2016 01:27 PM, Kees Cook 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?)
>
> You can kinda do it with /proc/$pid/(s)maps.  Here's smaps, for instance:
>
>> 00401000-00402000 --xp 00001000 08:14 4897479                            /root/pkeys/pkey-xonly
>> Size:                  4 kB
>> Rss:                   4 kB
> ...
>> KernelPageSize:        4 kB
>> MMUPageSize:           4 kB
>> Locked:                0 kB
>> ProtectionKey:        15
>> VmFlags: ex mr mw me dw

Ah-ha, perfect. Thanks!

> You can see "--x" and the ProtectionKey itself being nonzero.  That's a
> reasonable indication.  There's also the "OSPKE" cpuid bit which only
> shows up when the kernel has enabled protection keys.  This is
> _separate_ from the bit that says whether the processor support pkeys.
>
> I check them in test code like this:
>
>> static inline void __cpuid(unsigned int *eax, unsigned int *ebx,
>>                                 unsigned int *ecx, unsigned int *edx)
>> {
>>         /* ecx is often an input as well as an output. */
>>         asm volatile(
>>                 "cpuid;"
>>                 : "=a" (*eax),
>>                   "=b" (*ebx),
>>                   "=c" (*ecx),
>>                   "=d" (*edx)
>>                 : "0" (*eax), "2" (*ecx));
>> }
>>
>> /* Intel-defined CPU features, CPUID level 0x00000007:0 (ecx) */
>> #define X86_FEATURE_PKU        (1<<3) /* Protection Keys for Userspace */
>> #define X86_FEATURE_OSPKE      (1<<4) /* OS Protection Keys Enable */
>>
>> static inline int cpu_has_pku(void)
>> {
>>         unsigned int eax;
>>         unsigned int ebx;
>>         unsigned int ecx;
>>         unsigned int edx;
>>         eax = 0x7;
>>         ecx = 0x0;
>>         __cpuid(&eax, &ebx, &ecx, &edx);
>>
>>         if (!(ecx & X86_FEATURE_PKU)) {
>>                 dprintf2("cpu does not have PKU\n");
>>                 return 0;
>>         }
>>         if (!(ecx & X86_FEATURE_OSPKE)) {
>>                 dprintf2("cpu does not have OSPKE\n");
>>                 return 0;
>>         }
>>         return 1;
>> }
>

Great, thanks for the example!

-Kees

-- 
Kees Cook
Chrome OS & Brillo Security

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  reply	other threads:[~2016-02-17 21:36 UTC|newest]

Thread overview: 46+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-02-12 21:01 [PATCH 00/33] x86: Memory Protection Keys (v10) Dave Hansen
2016-02-12 21:01 ` [PATCH 01/33] mm: introduce get_user_pages_remote() Dave Hansen
2016-02-15  6:09   ` Balbir Singh
2016-02-15 16:29     ` Dave Hansen
2016-02-15  6:14   ` Srikar Dronamraju
2016-02-12 21:01 ` [PATCH 02/33] mm: overload get_user_pages() functions Dave Hansen
2016-02-16  8:36   ` Ingo Molnar
2016-02-17 18:15     ` Dave Hansen
2016-02-12 21:01 ` [PATCH 03/33] mm, gup: switch callers of get_user_pages() to not pass tsk/mm Dave Hansen
2016-02-12 21:01 ` [PATCH 04/33] x86, fpu: add placeholder for Processor Trace XSAVE state Dave Hansen
2016-02-12 21:02 ` [PATCH 05/33] x86, pkeys: Add Kconfig option Dave Hansen
2016-02-12 21:02 ` [PATCH 06/33] x86, pkeys: cpuid bit definition Dave Hansen
2016-02-12 21:02 ` [PATCH 07/33] x86, pkeys: define new CR4 bit Dave Hansen
2016-02-12 21:02 ` [PATCH 08/33] x86, pkeys: add PKRU xsave fields and data structure(s) Dave Hansen
2016-02-12 21:02 ` [PATCH 09/33] x86, pkeys: PTE bits for storing protection key Dave Hansen
2016-02-12 21:02 ` [PATCH 10/33] x86, pkeys: new page fault error code bit: PF_PK Dave Hansen
2016-02-12 21:02 ` [PATCH 11/33] x86, pkeys: store protection in high VMA flags Dave Hansen
2016-02-12 21:02 ` [PATCH 12/33] x86, pkeys: arch-specific protection bits Dave Hansen
2016-02-12 21:02 ` [PATCH 13/33] x86, pkeys: pass VMA down in to fault signal generation code Dave Hansen
2016-02-12 21:02 ` [PATCH 14/33] signals, pkeys: notify userspace about protection key faults Dave Hansen
2016-02-12 21:02 ` [PATCH 15/33] x86, pkeys: fill in pkey field in siginfo Dave Hansen
2016-02-12 21:02 ` [PATCH 16/33] x86, pkeys: add functions to fetch PKRU Dave Hansen
2016-02-12 21:02 ` [PATCH 17/33] mm: factor out VMA fault permission checking Dave Hansen
2016-02-12 21:02 ` [PATCH 18/33] x86, mm: simplify get_user_pages() PTE bit handling Dave Hansen
2016-02-12 21:02 ` [PATCH 19/33] x86, pkeys: check VMAs and PTEs for protection keys Dave Hansen
2016-02-12 21:02 ` [PATCH 20/33] mm: do not enforce PKEY permissions on "foreign" mm access Dave Hansen
2016-02-12 21:02 ` [PATCH 21/33] x86, pkeys: optimize fault handling in access_error() Dave Hansen
2016-02-12 21:02 ` [PATCH 22/33] x86, pkeys: differentiate instruction fetches Dave Hansen
2016-02-12 21:02 ` [PATCH 23/33] x86, pkeys: dump PKRU with other kernel registers Dave Hansen
2016-02-12 21:02 ` [PATCH 24/33] x86, pkeys: dump pkey from VMA in /proc/pid/smaps Dave Hansen
2016-02-12 21:02 ` [PATCH 25/33] x86, pkeys: add Kconfig prompt to existing config option Dave Hansen
2016-02-12 21:02 ` [PATCH 26/33] x86, pkeys: actually enable Memory Protection Keys in CPU Dave Hansen
2016-02-12 21:02 ` [PATCH 27/33] mm, multi-arch: pass a protection key in to calc_vm_flag_bits() Dave Hansen
2016-02-12 21:02 ` [PATCH 28/33] x86, pkeys: add arch_validate_pkey() Dave Hansen
2016-02-12 21:02 ` [PATCH 29/33] x86: separate out LDT init from context init Dave Hansen
2016-02-12 21:02 ` [PATCH 30/33] x86, fpu: allow setting of XSAVE state Dave Hansen
2016-02-12 21:02 ` [PATCH 31/33] x86, pkeys: allow kernel to modify user pkey rights register Dave Hansen
2016-02-12 21:02 ` [PATCH 32/33] x86, pkeys: create an x86 arch_calc_vm_prot_bits() for VMA flags Dave Hansen
2016-02-12 21:02 ` [PATCH 33/33] x86, pkeys: execute-only support Dave Hansen
2016-02-17 21:27   ` Kees Cook
2016-02-17 21:33     ` Dave Hansen
2016-02-17 21:36       ` Kees Cook [this message]
2016-02-17 22:17     ` Andy Lutomirski
2016-02-17 22:53       ` Dave Hansen
2016-02-18  0:46         ` Andy Lutomirski
2016-02-16  9:29 ` [PATCH 00/33] x86: Memory Protection Keys (v10) Ingo Molnar

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