linux-kernel - Re: [PATCH v7 0/5] printk: Userspace format indexing support

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Message-ID: <YMsfo3/b1LvOoiM0@alley>
Date:   Thu, 17 Jun 2021 12:10:43 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     Chris Down <chris@...isdown.name>
Cc:     linux-kernel@...r.kernel.org, Jessica Yu <jeyu@...nel.org>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        John Ogness <john.ogness@...utronix.de>,
        Steven Rostedt <rostedt@...dmis.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Kees Cook <keescook@...omium.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>, kernel-team@...com
Subject: Re: [PATCH v7 0/5] printk: Userspace format indexing support

On Tue 2021-06-15 17:52:20, Chris Down wrote:
> We have a number of systems industry-wide that have a subset of their
> functionality that works as follows:
> 
> 1. Receive a message from local kmsg, serial console, or netconsole;
> 2. Apply a set of rules to classify the message;
> 3. Do something based on this classification (like scheduling a
>    remediation for the machine), rinse, and repeat.
> 
> This provides a solution to the issue of silently changed or deleted
> printks: we record pointers to all printk format strings known at
> compile time into a new .printk_index section, both in vmlinux and
> modules. At runtime, this can then be iterated by looking at
> <debugfs>/printk/index/<module>, which emits the following format, both
> readable by humans and able to be parsed by machines:
> 
>     $ head -1 vmlinux; shuf -n 5 vmlinux
>     # <level[,flags]> filename:line function "format"
>     <5> block/blk-settings.c:661 disk_stack_limits "%s: Warning: Device %s is misaligned\n"
>     <4> kernel/trace/trace.c:8296 trace_create_file "Could not create tracefs '%s' entry\n"
>     <6> arch/x86/kernel/hpet.c:144 _hpet_print_config "hpet: %s(%d):\n"
>     <6> init/do_mounts.c:605 prepare_namespace "Waiting for root device %s...\n"
>     <6> drivers/acpi/osl.c:1410 acpi_no_auto_serialize_setup "ACPI: auto-serialization disabled\n"
> 
> This mitigates the majority of cases where we have a highly-specific
> printk which we want to match on, as we can now enumerate and check
> whether the format changed or the printk callsite disappeared entirely
> in userspace. This allows us to catch changes to printks we monitor
> earlier and decide what to do about it before it becomes problematic.
> 
> There is no additional runtime cost for printk callers or printk itself,
> and the assembly generated is exactly the same.
> 
> Chris Down (5):
>   string_helpers: Escape double quotes in escape_special
>   printk: Straighten out log_flags into printk_info_flags
>   printk: Rework parse_prefix into printk_parse_prefix
>   printk: Userspace format indexing support
>   printk: index: Add indexing support to dev_printk

The patchset looks ready for linux-next from my POV. I could fixup the
messages as suggested by Andy when pushing.

Well, I would still like to get acks from:

   + Andy for the 1st patch
   + Jessica for the changes in the module loader code in 4th patch.

Best Regards,
Petr