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From: Dave Hansen <dave.hansen@intel.com>
To: Ram Pai <linuxram@us.ibm.com>, Dave Hansen <dave.hansen@linux.intel.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	tglx@linutronix.de, mpe@ellerman.id.au, mingo@kernel.org,
	akpm@linux-foundation.org, shuah@kernel.org
Subject: Re: [PATCH 1/9] x86, pkeys: do not special case protection key 0
Date: Mon, 26 Mar 2018 21:11:48 -0700	[thread overview]
Message-ID: <0f990ce6-0eac-bd77-18d8-e2e3fdd5fb43@intel.com> (raw)
In-Reply-To: <20180327022718.GD5743@ram.oc3035372033.ibm.com>

On 03/26/2018 07:27 PM, Ram Pai wrote:
>> This is a bit nicer than what Ram proposed because it is simpler
>> and removes special-casing for pkey 0.  On the other hand, it does
>> allow applciations to pkey_free() pkey-0, but that's just a silly
>> thing to do, so we are not going to protect against it.
> The more I think about this, the more I feel we are opening up a can
> of worms.  I am ok with a bad application, shooting itself in its feet.
> But I am worried about all the bug reports and support requests we
> will encounter when applications inadvertently shoot themselves 
> and blame it on the kernel.
> 
> a warning in dmesg logs indicating a free-of-pkey-0 can help deflect
> the blame from the kernel.

I think it's OK to leave it.  A legit, very careful app could decide not
to use pkey 0.  It might even be fun to write that in the selftests for
sheer entertainment value.

Although, it _could_ be a bit more debuggable than it is now.  A
tracepoint that dumps out the pkey that got faulted on along with the
PKRU value at fault time might be nice to have.  That's mildly difficult
to do from outside the app.

  reply	other threads:[~2018-03-27  4:11 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-03-23 18:09 [PATCH 0/9] x86, pkeys: two protection keys bug fixes Dave Hansen
2018-03-23 18:09 ` [PATCH 1/9] x86, pkeys: do not special case protection key 0 Dave Hansen
2018-03-26 17:35   ` Ram Pai
2018-03-26 17:39     ` Dave Hansen
2018-03-27  2:27   ` Ram Pai
2018-03-27  4:11     ` Dave Hansen [this message]
2018-03-23 18:09 ` [PATCH 2/9] x86, pkeys, selftests: save off 'prot' for allocations Dave Hansen
2018-03-23 18:09 ` [PATCH 3/9] x86, pkeys, selftests: add a test for pkey 0 Dave Hansen
2018-03-23 18:09 ` [PATCH 4/9] x86, pkeys: override pkey when moving away from PROT_EXEC Dave Hansen
2018-03-23 19:15   ` Shakeel Butt
2018-03-23 19:23     ` Dave Hansen
2018-03-23 19:27       ` Shakeel Butt
2018-03-23 19:29         ` Dave Hansen
2018-03-23 19:38       ` Thomas Gleixner
2018-03-23 19:45         ` Thomas Gleixner
2018-03-23 19:48           ` Dave Hansen
2018-03-23 18:09 ` [PATCH 5/9] x86, pkeys, selftests: fix pointer math Dave Hansen
2018-03-23 18:09 ` [PATCH 6/9] x86, pkeys, selftests: fix pkey exhaustion test off-by-one Dave Hansen
2018-03-23 18:09 ` [PATCH 7/9] x86, pkeys, selftests: factor out "instruction page" Dave Hansen
2018-03-23 18:09 ` [PATCH 8/9] x86, pkeys, selftests: add allow faults on unknown keys Dave Hansen
2018-03-23 18:09 ` [PATCH 9/9] x86, pkeys, selftests: add PROT_EXEC test Dave Hansen
2018-03-26 17:27 [PATCH 0/9] [v2] x86, pkeys: two protection keys bug fixes Dave Hansen
2018-03-26 17:27 ` [PATCH 1/9] x86, pkeys: do not special case protection key 0 Dave Hansen
2018-03-26 17:47   ` Shuah Khan
2018-03-26 17:53     ` Dave Hansen
2018-03-26 17:58       ` Shuah Khan
2018-04-27 17:45 [PATCH 0/9] [v3] x86, pkeys: two protection keys bug fixes Dave Hansen
2018-04-27 17:45 ` [PATCH 1/9] x86, pkeys: do not special case protection key 0 Dave Hansen

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