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    Subject[PATCH mm v4 22/39] kasan, fork: reset pointer tags of vmapped stacks
    Date
    From: Andrey Konovalov <andreyknvl@google.com>

    Once tag-based KASAN modes start tagging vmalloc() allocations,
    kernel stacks start getting tagged if CONFIG_VMAP_STACK is enabled.

    Reset the tag of kernel stack pointers after allocation in
    alloc_thread_stack_node().

    For SW_TAGS KASAN, when CONFIG_KASAN_STACK is enabled, the
    instrumentation can't handle the SP register being tagged.

    For HW_TAGS KASAN, there's no instrumentation-related issues. However,
    the impact of having a tagged SP register needs to be properly evaluated,
    so keep it non-tagged for now.

    Note, that the memory for the stack allocation still gets tagged to
    catch vmalloc-into-stack out-of-bounds accesses.

    Signed-off-by: Andrey Konovalov <andreyknvl@google.com>

    ---

    Changes v2->v3:
    - Update patch description.
    ---
    kernel/fork.c | 1 +
    1 file changed, 1 insertion(+)

    diff --git a/kernel/fork.c b/kernel/fork.c
    index 403b9dbbfb62..4125373dba4e 100644
    --- a/kernel/fork.c
    +++ b/kernel/fork.c
    @@ -254,6 +254,7 @@ static unsigned long *alloc_thread_stack_node(struct task_struct *tsk, int node)
    * so cache the vm_struct.
    */
    if (stack) {
    + stack = kasan_reset_tag(stack);
    tsk->stack_vm_area = find_vm_area(stack);
    tsk->stack = stack;
    }
    --
    2.25.1
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