From: Florian Weimer <fweimer@redhat.com>
To: Ram Pai <linuxram@us.ibm.com>
Cc: mpe@ellerman.id.au, mingo@redhat.com, akpm@linux-foundation.org,
linuxppc-dev@lists.ozlabs.org, linux-mm@kvack.org,
x86@kernel.org, linux-arch@vger.kernel.org,
linux-kernel@vger.kernel.org, dave.hansen@intel.com,
benh@kernel.crashing.org, paulus@samba.org,
khandual@linux.vnet.ibm.com, aneesh.kumar@linux.vnet.ibm.com,
bsingharora@gmail.com, hbabu@us.ibm.com, mhocko@kernel.org,
bauerman@linux.vnet.ibm.com, ebiederm@xmission.com,
corbet@lwn.net, arnd@arndb.de, msuchanek@suse.com,
Ulrich.Weigand@de.ibm.com
Subject: Re: [PATCH] x86, powerpc : pkey-mprotect must allow pkey-0
Date: Wed, 14 Mar 2018 09:05:30 +0100 [thread overview]
Message-ID: <0a6981b3-dcd2-4dce-3209-7f8055d8548f@redhat.com> (raw)
In-Reply-To: <f71b583f-2b66-e9ed-b08b-fddff228a5a7@redhat.com>
On 03/14/2018 09:00 AM, Florian Weimer wrote:
> On 03/09/2018 09:00 PM, Ram Pai wrote:
>> On Fri, Mar 09, 2018 at 12:04:49PM +0100, Florian Weimer wrote:
>>> On 03/09/2018 09:12 AM, Ram Pai wrote:
>>>> Once an address range is associated with an allocated pkey, it
>>>> cannot be
>>>> reverted back to key-0. There is no valid reason for the above
>>>> behavior.
>>>
>>> mprotect without a key does not necessarily use key 0, e.g. if
>>> protection keys are used to emulate page protection flag combination
>>> which is not directly supported by the hardware.
>>>
>>> Therefore, it seems to me that filtering out non-allocated keys is
>>> the right thing to do.
>>
>> I am not sure, what you mean. Do you agree with the patch or otherwise?
>
> I think it's inconsistent to make key 0 allocated, but not the key which
> is used for PROT_EXEC emulation, which is still reserved. Even if you
> change the key 0 behavior, it is still not possible to emulate mprotect
> behavior faithfully with an allocated key.
Ugh. Should have read the code first before replying:
/* Do we need to assign a pkey for mm's execute-only maps? */
if (execute_only_pkey == -1) {
/* Go allocate one to use, which might fail */
execute_only_pkey = mm_pkey_alloc(mm);
if (execute_only_pkey < 0)
return -1;
need_to_set_mm_pkey = true;
}
So we do allocate the PROT_EXEC-only key, and I assume it means that the
key can be restored using pkey_mprotect. So the key 0 behavior is a
true exception after all, and it makes sense to realign the behavior
with the other keys.
Thanks,
Florian
next prev parent reply other threads:[~2018-03-14 8:05 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-03-09 8:12 [PATCH] x86, powerpc : pkey-mprotect must allow pkey-0 Ram Pai
2018-03-09 8:37 ` Balbir Singh
2018-03-09 19:54 ` Ram Pai
2018-03-09 8:43 ` Ingo Molnar
2018-03-09 20:09 ` Ram Pai
2018-03-09 10:19 ` Michael Ellerman
2018-03-09 20:06 ` Ram Pai
2018-03-12 15:46 ` Dave Hansen
2018-03-09 11:04 ` Florian Weimer
2018-03-09 20:00 ` Ram Pai
2018-03-14 8:00 ` Florian Weimer
2018-03-14 8:05 ` Florian Weimer [this message]
2018-03-14 14:08 ` Dave Hansen
2018-03-09 22:40 ` Dave Hansen
2018-03-10 5:55 ` Ram Pai
2018-03-10 6:50 ` Dave Hansen
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