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    Subject[PATCH v19 05/15] mm: untag user pointers in mm/gup.c
    From
    This patch is a part of a series that extends kernel ABI to allow to pass
    tagged user pointers (with the top byte set to something else other than
    0x00) as syscall arguments.

    mm/gup.c provides a kernel interface that accepts user addresses and
    manipulates user pages directly (for example get_user_pages, that is used
    by the futex syscall). Since a user can provided tagged addresses, we need
    to handle this case.

    Add untagging to gup.c functions that use user addresses for vma lookups.

    Reviewed-by: Khalid Aziz <khalid.aziz@oracle.com>
    Reviewed-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
    Reviewed-by: Kees Cook <keescook@chromium.org>
    Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
    Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
    ---
    mm/gup.c | 4 ++++
    1 file changed, 4 insertions(+)

    diff --git a/mm/gup.c b/mm/gup.c
    index 98f13ab37bac..1c1c97ec63df 100644
    --- a/mm/gup.c
    +++ b/mm/gup.c
    @@ -799,6 +799,8 @@ static long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
    if (!nr_pages)
    return 0;

    + start = untagged_addr(start);
    +
    VM_BUG_ON(!!pages != !!(gup_flags & FOLL_GET));

    /*
    @@ -961,6 +963,8 @@ int fixup_user_fault(struct task_struct *tsk, struct mm_struct *mm,
    struct vm_area_struct *vma;
    vm_fault_t ret, major = 0;

    + address = untagged_addr(address);
    +
    if (unlocked)
    fault_flags |= FAULT_FLAG_ALLOW_RETRY;

    --
    2.22.0.709.g102302147b-goog
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