a question about protection_map[]

From	Xishi Qiu <qiuxishi@huawei.com>
Newsgroups	linux.kernel
Subject	a question about protection_map[]
Date	2016-07-11 12:20 +0200
Message-ID	<rTGtH-5FU-1@gated-at.bofh.it> (permalink)
Organization	linux.* mail to news gateway

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Hi,

We can use mprotect to set read only or read/write.

mprotect_fixup()
	vma_set_page_prot()
		vm_pgprot_modify()
			vm_get_page_prot()
				protection_map[vm_flags & (VM_READ|VM_WRITE|VM_EXEC|VM_SHARED)]

The following code shows that prots from __P001(PROT_READ) and __P010(PROT_WRITE)
are the same, so how does it distinguish read only or read/write from mprotect?

pgprot_t protection_map[16] = {
	__P000, __P001, __P010, __P011, __P100, __P101, __P110, __P111,
	__S000, __S001, __S010, __S011, __S100, __S101, __S110, __S111
};

#define __P001	PAGE_READONLY
#define __P010	PAGE_COPY

#define PAGE_READONLY		__pgprot(_PAGE_PRESENT | _PAGE_USER |	\
					 _PAGE_ACCESSED | _PAGE_NX)

#define PAGE_COPY_NOEXEC	__pgprot(_PAGE_PRESENT | _PAGE_USER |	\
					 _PAGE_ACCESSED | _PAGE_NX)
#define PAGE_COPY		PAGE_COPY_NOEXEC


Thanks,
Xishi Qiu

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a question about protection_map[] Xishi Qiu <qiuxishi@huawei.com> - 2016-07-11 12:20 +0200
  Re: a question about protection_map[] "Kirill A. Shutemov" <kirill@shutemov.name> - 2016-07-11 15:40 +0200
    Re: a question about protection_map[] Xishi Qiu <qiuxishi@huawei.com> - 2016-07-12 03:40 +0200
      Re: a question about protection_map[] "Kirill A. Shutemov" <kirill@shutemov.name> - 2016-07-12 03:50 +0200

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