• Christophe Leroy's avatar
    powerpc/hugetlb: fix page rights verification in gup_hugepte() · ca8afd40
    Christophe Leroy authored
    gup_hugepte() checks if pages are present and readable, and
    when  'write' is set, also checks if the pages are writable.
    
    Initially this was done by checking if _PAGE_PRESENT and
    _PAGE_READ were set. In addition, _PAGE_WRITE was verified for write
    accesses.
    
    The problem is that we have to handle the three following cases:
    1/ The target defines __PAGE_READ and __PAGE_WRITE
    2/ The target defines __PAGE_RW
    3/ The target defines __PAGE_RO
    
    In case 1/, this is obvious
    In case 2/, __PAGE_READ is defined as 0 and __PAGE_WRITE as __PAGE_RW
    so it works as well.
    But in case 3, __PAGE_RW is defined as 0, which means __PAGE_WRITE is 0
    and then the test returns true (page writable) in all cases.
    
    A first correction was attempted in commit 6b8cb66a ("powerpc: Fix
    usage of _PAGE_RO in hugepage"), but that fix is wrong:
    instead of checking that the page is writable when write is requested,
    it checks that the page is NOT writable when write is NOT requested.
    
    This patch adds a new pte_read() helper to check whether a page is
    readable or not. This avoids handling all possible cases in
    gup_hugepte().
    
    Then gup_hugepte() is modified to use pte_present(), pte_read()
    and pte_write() instead of the raw flags.
    Signed-off-by: default avatarChristophe Leroy <christophe.leroy@c-s.fr>
    Reviewed-by: default avatarAneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
    Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
    ca8afd40
pgtable.h 15 KB