Messages in this thread | | | From | Kees Cook <> | Date | Thu, 29 Sep 2016 18:36:26 -0700 | Subject | Re: [RFC PATCH v1 0/2] printk: Shared kernel logging |
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On Thu, Sep 29, 2016 at 5:55 PM, Sean Hudson <sean_hudson@mentor.com> wrote: > This patch set is based on Linus' v4.8-rc8 tag. > > This debug feature allows the kernel to use an external buffer and control > block for kernel log messages. The feature is controlled by an optional > command line parameter. The existing buffer and control block can contain > existing log messages from previous boot cycles and/or the bootloader. The > command line parameter was chosen for flexibility, cross arch portability, > and the ability to dynamically enable/disable this feature. The parameter > specifies the address of a control block used to replace the default log > buffer. Existing bootloader and kernel log messages are kept, in order, > inside the new buffer. After a boot that preserves the buffer contents, a > bootloader can display both kernel and bootloader log entries from multiple, > previous boots. It also allows the kernel to display bootloader log entries > along with its own messages. > > This feature is intended for debug purposes and has no effect unless the > command line parameter is specified. Further, it validates the passed > control block carefully and if any checks fail, it falls back to the default > behaviour. As such, it can be left enabled by default. > > Memory Reservation > > This feature expects the bootloader to reserve/preserve the shared buffer > memory. This reservation needs to prevent the kernel from overwriting the > external log control block and log entries. In my testing, I've used the > 'fdt' commands in uboot to dynamically inject reserved memory regions via > the DT to the kernel.
Interesting! I wonder if this can be adjusted to incorporate the existing console logging feature in the pstore which does a similar thing? Though pstore doesn't know about bootloader logs, really, it's just storing kernel logs in a ring buffer. Maybe this can provide a backend to pstore or something, especially since pstore initialization happens "too late" for this to really be very sensible. It just seems like it'd be nice to have a single persistent console memory region...
-Kees
> > Sean Hudson (2): > printk: collect offsets into replaceable structure > printk: external log buffer (CONFIG_LOGBUFFER) > > init/Kconfig | 12 + > init/main.c | 2 + > kernel/printk/printk.c | 598 +++++++++++++++++++++++++++++++++++-------------- > 3 files changed, 445 insertions(+), 167 deletions(-) > > -- > 1.9.1 > >
-- Kees Cook Nexus Security
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