a question about protection_map[]

[Xishi Qiu]

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