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    Subject[PATCH 4.19 64/80] x86/unwind/orc: Fix error handling in __unwind_start()
    Date
    From: Josh Poimboeuf <jpoimboe@redhat.com>

    commit 71c95825289f585014fe9741b051d32a7a916680 upstream.

    The unwind_state 'error' field is used to inform the reliable unwinding
    code that the stack trace can't be trusted. Set this field for all
    errors in __unwind_start().

    Also, move the zeroing out of the unwind_state struct to before the ORC
    table initialization check, to prevent the caller from reading
    uninitialized data if the ORC table is corrupted.

    Fixes: af085d9084b4 ("stacktrace/x86: add function for detecting reliable stack traces")
    Fixes: d3a09104018c ("x86/unwinder/orc: Dont bail on stack overflow")
    Fixes: 98d0c8ebf77e ("x86/unwind/orc: Prevent unwinding before ORC initialization")
    Reported-by: Pavel Machek <pavel@denx.de>
    Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
    Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    Link: https://lkml.kernel.org/r/d6ac7215a84ca92b895fdd2e1aa546729417e6e6.1589487277.git.jpoimboe@redhat.com
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    arch/x86/kernel/unwind_orc.c | 16 +++++++++-------
    1 file changed, 9 insertions(+), 7 deletions(-)

    --- a/arch/x86/kernel/unwind_orc.c
    +++ b/arch/x86/kernel/unwind_orc.c
    @@ -589,23 +589,23 @@ EXPORT_SYMBOL_GPL(unwind_next_frame);
    void __unwind_start(struct unwind_state *state, struct task_struct *task,
    struct pt_regs *regs, unsigned long *first_frame)
    {
    - if (!orc_init)
    - goto done;
    -
    memset(state, 0, sizeof(*state));
    state->task = task;

    + if (!orc_init)
    + goto err;
    +
    /*
    * Refuse to unwind the stack of a task while it's executing on another
    * CPU. This check is racy, but that's ok: the unwinder has other
    * checks to prevent it from going off the rails.
    */
    if (task_on_another_cpu(task))
    - goto done;
    + goto err;

    if (regs) {
    if (user_mode(regs))
    - goto done;
    + goto the_end;

    state->ip = regs->ip;
    state->sp = kernel_stack_pointer(regs);
    @@ -638,6 +638,7 @@ void __unwind_start(struct unwind_state
    * generate some kind of backtrace if this happens.
    */
    void *next_page = (void *)PAGE_ALIGN((unsigned long)state->sp);
    + state->error = true;
    if (get_stack_info(next_page, state->task, &state->stack_info,
    &state->stack_mask))
    return;
    @@ -663,8 +664,9 @@ void __unwind_start(struct unwind_state

    return;

    -done:
    +err:
    + state->error = true;
    +the_end:
    state->stack_info.type = STACK_TYPE_UNKNOWN;
    - return;
    }
    EXPORT_SYMBOL_GPL(__unwind_start);

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