lkml.org 
[lkml]   [2018]   [Aug]   [1]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    From
    Subject[PATCH 4.14 020/246] kcov: ensure irq code sees a valid area
    Date
    4.14-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Mark Rutland <mark.rutland@arm.com>

    [ Upstream commit c9484b986ef03492357fddd50afbdd02929cfa72 ]

    Patch series "kcov: fix unexpected faults".

    These patches fix a few issues where KCOV code could trigger recursive
    faults, discovered while debugging a patch enabling KCOV for arch/arm:

    * On CONFIG_PREEMPT kernels, there's a small race window where
    __sanitizer_cov_trace_pc() can see a bogus kcov_area.

    * Lazy faulting of the vmalloc area can cause mutual recursion between
    fault handling code and __sanitizer_cov_trace_pc().

    * During the context switch, switching the mm can cause the kcov_area to
    be transiently unmapped.

    These are prerequisites for enabling KCOV on arm, but the issues
    themsevles are generic -- we just happen to avoid them by chance rather
    than design on x86-64 and arm64.

    This patch (of 3):

    For kernels built with CONFIG_PREEMPT, some C code may execute before or
    after the interrupt handler, while the hardirq count is zero. In these
    cases, in_task() can return true.

    A task can be interrupted in the middle of a KCOV_DISABLE ioctl while it
    resets the task's kcov data via kcov_task_init(). Instrumented code
    executed during this period will call __sanitizer_cov_trace_pc(), and as
    in_task() returns true, will inspect t->kcov_mode before trying to write
    to t->kcov_area.

    In kcov_init_task() we update t->kcov_{mode,area,size} with plain stores,
    which may be re-ordered, torn, etc. Thus __sanitizer_cov_trace_pc() may
    see bogus values for any of these fields, and may attempt to write to
    memory which is not mapped.

    Let's avoid this by using WRITE_ONCE() to set t->kcov_mode, with a
    barrier() to ensure this is ordered before we clear t->kov_{area,size}.
    This ensures that any code execute while kcov_init_task() is preempted
    will either see valid values for t->kcov_{area,size}, or will see that
    t->kcov_mode is KCOV_MODE_DISABLED, and bail out without touching
    t->kcov_area.

    Link: http://lkml.kernel.org/r/20180504135535.53744-2-mark.rutland@arm.com
    Signed-off-by: Mark Rutland <mark.rutland@arm.com>
    Acked-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
    Cc: Dmitry Vyukov <dvyukov@google.com>
    Cc: Ingo Molnar <mingo@redhat.com>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    kernel/kcov.c | 3 ++-
    1 file changed, 2 insertions(+), 1 deletion(-)

    --- a/kernel/kcov.c
    +++ b/kernel/kcov.c
    @@ -108,7 +108,8 @@ static void kcov_put(struct kcov *kcov)

    void kcov_task_init(struct task_struct *t)
    {
    - t->kcov_mode = KCOV_MODE_DISABLED;
    + WRITE_ONCE(t->kcov_mode, KCOV_MODE_DISABLED);
    + barrier();
    t->kcov_size = 0;
    t->kcov_area = NULL;
    t->kcov = NULL;

    \
     
     \ /
      Last update: 2018-08-01 19:55    [W:4.119 / U:0.132 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site