linux-kernel - x86: a question about protection

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Date:	Sun, 13 Dec 2015 16:41:07 +0800
From:	Xishi Qiu <qiuxishi@...wei.com>
To:	LKML <linux-kernel@...r.kernel.org>, Linux MM <linux-mm@...ck.org>
Subject: x86: a question about protection_map

When we use mprotect to change the page prot, I find "__P001" and "__P011"
are the same. So how we detect the write/read?

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

pgprot_t vm_get_page_prot(unsigned long vm_flags)
{
	return __pgprot(pgprot_val(protection_map[vm_flags &
				(VM_READ|VM_WRITE|VM_EXEC|VM_SHARED)]) |
			pgprot_val(arch_vm_get_page_prot(vm_flags)));
}

#define __P001	PAGE_READONLY
#define __P011	PAGE_COPY

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

Thanks,
Xishi Qiu

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