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From: Ram Pai <linuxram@us.ibm.com>
To: Dave Hansen <dave.hansen@linux.intel.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	tglx@linutronix.de, dave.hansen@intel.com, 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 19:27:18 -0700	[thread overview]
Message-ID: <20180327022718.GD5743@ram.oc3035372033.ibm.com> (raw)
In-Reply-To: <20180323180905.B40984E6@viggo.jf.intel.com>

On Fri, Mar 23, 2018 at 11:09:05AM -0700, Dave Hansen wrote:
> 
> From: Dave Hansen <dave.hansen@linux.intel.com>
> 
> mm_pkey_is_allocated() treats pkey 0 as unallocated.  That is
> inconsistent with the manpages, and also inconsistent with
> mm->context.pkey_allocation_map.  Stop special casing it and only
> disallow values that are actually bad (< 0).
> 
> The end-user visible effect of this is that you can now use
> mprotect_pkey() to set pkey=0.
> 
> 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.

RP

  parent reply	other threads:[~2018-03-27  2:27 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 [this message]
2018-03-27  4:11     ` Dave Hansen
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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