Re: [PATCH v2 0/8] ring-buffer/tracing: Save module information in persistent memory

[Masami Hiramatsu (Google) <mhiramat@kernel.org>]

On Fri, 14 Feb 2025 22:43:01 -0500
Steven Rostedt <rostedt@goodmis.org> wrote:

> 
> This updates the persistent instance to record what modules were
> loaded and what addresses they were loaded at.
> 
> First the KASLR offset is recorded in the persistent ring buffer instead of
> a text address. This can be used to calculated the address offset.
> 
> Next the persistent memory is divided up differently so that there's
> a single global meta data for the entire buffer that can hold the
> global data, and each per CPU meta data can just hold what it needs.
> 
> A scratch area can be created by the caller, in this case the tracing
> system, to store data in the persistent memory area.
> 
> As the KASLR offset is only needed by the tracer, that data is moved
> from the ring buffer meta data into this new storage.
> 
> Next the modules that are loaded and where they are loaded is stored in this
> new persistent storage.
> 
> The module list along with the KASLR offset is now exposed in the
> last_boot_info if the buffer is from a previous boot. If it is from the
> current boot, the file will only contain:
> 
>    # Current
> 
> in order to not leak the KASLR offset.
> 
> Finally, when new modules are loaded while the trace is active, they too
> will be added to this persistent memory. Note, if tracing is stopped, and
> then restarted, it clears the module list and will reload all the modules
> again so that it doesn't need to keep track of what is loaded or unloaded
> while no tracing is going on.

The series looks good to me.

Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org> for this series.

Thanks,

> 
> Changes since v1: https://lore.kernel.org/all/20250205225031.799739376@goodmis.org/
> 
> - Rebased on top of the urgent branch
> 
> - Allow the size of the scratch area in the persistent ring buffer to be
>   defined by the caller.
> 
> - Change the output of the last_boot_info to show the kaslr instead of:
>   "Offset: <offset>" to "<offset>\t[kernel]" to make it consistent with
>   the module output.
> 
> 
> Steven Rostedt (8):
>       ring-buffer: Use kaslr address instead of text delta
>       ring-buffer: Add buffer meta data for persistent ring buffer
>       ring-buffer: Add ring_buffer_meta_scratch()
>       tracing: Have persistent trace instances save KASLR offset
>       module: Add module_for_each_mod() function
>       tracing: Have persistent trace instances save module addresses
>       tracing: Show module names and addresses of last boot
>       tracing: Update modules to persistent instances when loaded
> 
> ----
>  include/linux/module.h      |   6 +
>  include/linux/ring_buffer.h |   8 +-
>  kernel/module/main.c        |  14 +++
>  kernel/trace/ring_buffer.c  | 245 ++++++++++++++++++++++++-----------------
>  kernel/trace/trace.c        | 263 ++++++++++++++++++++++++++++++++++++++++----
>  kernel/trace/trace.h        |  15 ++-
>  kernel/trace/trace_events.c |  40 +++++--
>  7 files changed, 448 insertions(+), 143 deletions(-)


-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>