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    Subject[PATCH 2/3] perf, x86: Don't leak kernel data via callchains
    Date
    The NMI could fire when the kernel has done set_fs(KERNEL_DS).
    Since we're interested in user space stack pointers only,
    check against USER_DS explicitly.

    Signed-off-by: Arun Sharma <asharma@fb.com>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Ingo Molnar <mingo@elte.hu>
    Cc: linux-kernel@vger.kernel.org
    ---
    arch/x86/kernel/cpu/perf_event.c | 8 +++++++-
    1 files changed, 7 insertions(+), 1 deletions(-)

    diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
    index 9f98636..ccd8c07 100644
    --- a/arch/x86/kernel/cpu/perf_event.c
    +++ b/arch/x86/kernel/cpu/perf_event.c
    @@ -1803,6 +1803,7 @@ perf_callchain_user(struct perf_callchain_entry *entry, struct pt_regs *regs)
    {
    struct stack_frame frame;
    const void __user *fp;
    + mm_segment_t oldfs = get_fs();

    if (perf_guest_cbs && perf_guest_cbs->is_in_guest()) {
    /* TODO: We don't support guest os callchain now */
    @@ -1816,8 +1817,9 @@ perf_callchain_user(struct perf_callchain_entry *entry, struct pt_regs *regs)
    if (!current->mm)
    return;

    + set_fs(USER_DS);
    if (perf_callchain_user32(regs, entry))
    - return;
    + goto out;

    while (entry->nr < PERF_MAX_STACK_DEPTH) {
    unsigned long bytes;
    @@ -1831,6 +1833,10 @@ perf_callchain_user(struct perf_callchain_entry *entry, struct pt_regs *regs)
    perf_callchain_store(entry, frame.return_address);
    fp = frame.next_frame;
    }
    +
    +out:
    + set_fs(oldfs);
    + return;
    }

    unsigned long perf_instruction_pointer(struct pt_regs *regs)
    --
    1.7.8.4


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