linux-kernel - Re: [PATCH 27/34] x86, pkeys: make mprotect_key() mask off additional vm

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Message-ID: <alpine.DEB.2.11.1512081941040.3595@nanos>
Date:	Tue, 8 Dec 2015 19:41:53 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Dave Hansen <dave@...1.net>
cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org, x86@...nel.org,
	dave.hansen@...ux.intel.com
Subject: Re: [PATCH 27/34] x86, pkeys: make mprotect_key() mask off additional
 vm_flags

On Thu, 3 Dec 2015, Dave Hansen wrote:
> 
> From: Dave Hansen <dave.hansen@...ux.intel.com>
> 
> Today, mprotect() takes 4 bits of data: PROT_READ/WRITE/EXEC/NONE.
> Three of those bits: READ/WRITE/EXEC get translated directly in to
> vma->vm_flags by calc_vm_prot_bits().  If a bit is unset in
> mprotect()'s 'prot' argument then it must be cleared in vma->vm_flags
> during the mprotect() call.
> 
> We do the by first calculating the VMA flags we want set, then
> clearing the ones we do not want to inherit from the original VMA:
> 
> 	vm_flags = calc_vm_prot_bits(prot, key);
> 	...
> 	newflags = vm_flags;
> 	newflags |= (vma->vm_flags & ~(VM_READ | VM_WRITE | VM_EXEC));
> 
> However, we *also* want to mask off the original VMA's vm_flags in
> which we store the protection key.
> 
> To do that, this patch adds a new macro:
> 
> 	ARCH_VM_FLAGS_AFFECTED_BY_MPROTECT

-ENOSUCHMACRO
 
> which allows the architecture to specify additional bits that it would
> like cleared.  We use that to ensure that the VM_PKEY_BIT* bits get
> cleared.

Other than that: Reviewed-by: Thomas Gleixner <tglx@...utronix.de>
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