ULONG NTAPI MiMakeProtectionMask ( IN ULONG Protect )
Definition at line 112 of file section.c.
{
    ULONG Mask1, Mask2, ProtectMask;

    /* PAGE_EXECUTE_WRITECOMBINE is theoretically the maximum */
    if (Protect >= (PAGE_WRITECOMBINE * 2)) return MM_INVALID_PROTECTION;

    /*
     * Windows API protection mask can be understood as two bitfields, differing
     * by whether or not execute rights are being requested
     */
    Mask1 = Protect & 0xF;
    Mask2 = (Protect >> 4) & 0xF;

    /* Check which field is there */
    if (!Mask1)
    {
        /* Mask2 must be there, use it to determine the PTE protection */
        if (!Mask2) return MM_INVALID_PROTECTION;
        ProtectMask = MmUserProtectionToMask2[Mask2];
    }
    else
    {
        /* Mask2 should not be there, use Mask1 to determine the PTE mask */
        if (Mask2) return MM_INVALID_PROTECTION;
        ProtectMask = MmUserProtectionToMask1[Mask1];
    }

    /* Make sure the final mask is a valid one */
    if (ProtectMask == MM_INVALID_PROTECTION) return MM_INVALID_PROTECTION;

    /* Check for PAGE_GUARD option */
    if (Protect & PAGE_GUARD)
    {
        /* It's not valid on no-access, nocache, or writecombine pages */
        if ((ProtectMask == MM_NOACCESS) ||
            (Protect & (PAGE_NOCACHE | PAGE_WRITECOMBINE)))
        {
            /* Fail such requests */
            return MM_INVALID_PROTECTION;
        }

        /* This actually turns on guard page in this scenario! */
        ProtectMask |= MM_DECOMMIT;
    }

    /* Check for nocache option */
    if (Protect & PAGE_NOCACHE)
    {
        /* The earlier check should've eliminated this possibility */
        ASSERT((Protect & PAGE_GUARD) == 0);

        /* Check for no-access page or write combine page */
        if ((ProtectMask == MM_NOACCESS) || (Protect & PAGE_WRITECOMBINE))
        {
            /* Such a request is invalid */
            return MM_INVALID_PROTECTION;
        }

        /* Add the PTE flag */
        ProtectMask |= MM_NOCACHE;
    }

    /* Check for write combine option */
    if (Protect & PAGE_WRITECOMBINE)
    {
        /* The two earlier scenarios should've caught this */
        ASSERT((Protect & (PAGE_GUARD | PAGE_NOACCESS)) == 0);

        /* Don't allow on no-access pages */
        if (ProtectMask == MM_NOACCESS) return MM_INVALID_PROTECTION;

        /* This actually turns on write-combine in this scenario! */
        ProtectMask |= MM_NOACCESS;
    }

    /* Return the final MM PTE protection mask */
    return ProtectMask;
}
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