linux-kernel - Re: [PATCH, RFC 09/62] x86/mm: Preserve KeyID on pte_modify() and pgprot

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Message-ID: <20190614130322.zbpubyxcncysgyi3@box>
Date:   Fri, 14 Jun 2019 16:03:22 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...capital.net>,
        David Howells <dhowells@...hat.com>,
        Kees Cook <keescook@...omium.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Kai Huang <kai.huang@...ux.intel.com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        Alison Schofield <alison.schofield@...el.com>,
        linux-mm@...ck.org, kvm@...r.kernel.org, keyrings@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH, RFC 09/62] x86/mm: Preserve KeyID on pte_modify() and
 pgprot_modify()

On Fri, Jun 14, 2019 at 11:15:14AM +0200, Peter Zijlstra wrote:
> On Wed, May 08, 2019 at 05:43:29PM +0300, Kirill A. Shutemov wrote:
> > + * Cast PAGE_MASK to a signed type so that it is sign-extended if
> > + * virtual addresses are 32-bits but physical addresses are larger
> > + * (ie, 32-bit PAE).
> 
> On 32bit, 'long' is still 32bit, did you want to cast to 'long long'
> instead? Ideally we'd use pteval_t here, but I see that is unsigned.

It will be cased implecitly to unsigned long long by '& ((1ULL <<
__PHYSICAL_MASK_SHIFT) - 1)' and due to sign-extension it will get it
right for PAE.

Just to be on safe side, I've re-checked that nothing changed for PAE by
the patch using the test below. PTE_PFN_MASK and PTE_PFN_MASK_MAX are
identical when compiled with -m32.

> >   */
> > -#define _PAGE_CHG_MASK	(PTE_PFN_MASK | _PAGE_PCD | _PAGE_PWT |		\
> > +#define PTE_PFN_MASK_MAX \
> > +	(((signed long)PAGE_MASK) & ((1ULL << __PHYSICAL_MASK_SHIFT) - 1))
> > +#define _PAGE_CHG_MASK	(PTE_PFN_MASK_MAX | _PAGE_PCD | _PAGE_PWT |		\
> >  			 _PAGE_SPECIAL | _PAGE_ACCESSED | _PAGE_DIRTY |	\
> >  			 _PAGE_SOFT_DIRTY | _PAGE_DEVMAP)
> >  #define _HPAGE_CHG_MASK (_PAGE_CHG_MASK | _PAGE_PSE)
> 

#include <stdio.h>

typedef unsigned long long u64;
typedef u64 pteval_t;
typedef u64 phys_addr_t;

#define PAGE_SHIFT		12
#define PAGE_SIZE		(1UL << PAGE_SHIFT)
#define PAGE_MASK		(~(PAGE_SIZE-1))
#define __PHYSICAL_MASK_SHIFT	52
#define __PHYSICAL_MASK		((phys_addr_t)((1ULL << __PHYSICAL_MASK_SHIFT) - 1))
#define PHYSICAL_PAGE_MASK	(((signed long)PAGE_MASK) & __PHYSICAL_MASK)
#define PTE_PFN_MASK		((pteval_t)PHYSICAL_PAGE_MASK)
#define PTE_PFN_MASK_MAX	(((signed long)PAGE_MASK) & ((1ULL << __PHYSICAL_MASK_SHIFT) - 1))

int main(void)
{
	printf("PTE_PFN_MASK: %#llx\n", PTE_PFN_MASK);
	printf("PTE_PFN_MASK_MAX: %#llx\n", PTE_PFN_MASK_MAX);

	return 0;
}
-- 
 Kirill A. Shutemov