linux-hardening - Re: [POC][RFC][PATCH 2/2] pstore/ramoops: Add ramoops.mem

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Date: Tue, 9 Apr 2024 15:18:45 -0700
From: Kees Cook <keescook@...omium.org>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Liam R. Howlett" <Liam.Howlett@...cle.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Lorenzo Stoakes <lstoakes@...il.com>, linux-mm@...ck.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
	"H. Peter Anvin" <hpa@...or.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Tony Luck <tony.luck@...el.com>,
	"Guilherme G. Piccoli" <gpiccoli@...lia.com>,
	linux-hardening@...r.kernel.org, Guenter Roeck <linux@...ck-us.net>,
	Ross Zwisler <zwisler@...gle.com>, wklin@...gle.com,
	Vineeth Remanan Pillai <vineeth@...byteword.org>,
	Joel Fernandes <joel@...lfernandes.org>,
	Suleiman Souhlal <suleiman@...gle.com>,
	Linus Torvalds <torvalds@...uxfoundation.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>
Subject: Re: [POC][RFC][PATCH 2/2] pstore/ramoops: Add ramoops.mem_name=
 command line option

On Tue, Apr 09, 2024 at 05:02:56PM -0400, Steven Rostedt wrote:
> From: "Steven Rostedt (Google)" <rostedt@...dmis.org>
> 
> Add a method to find a region specified by memmap=nn*align:name for
> ramoops. Adding a kernel command line parameter:
> 
>   memmap=12M*4096:oops ramoops.mem_name=oops
> 
> Will use the size and location defined by the memmap parameter where it
> finds the memory and labels it "oops". The "oops" in the ramoops option
> is used to search for it.
> 
> This allows for arbitrary RAM to be used for ramoops if it is known that
> the memory is not cleared on kernel crashes or soft reboots.
> 
> Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
> ---
>  fs/pstore/ram.c | 18 ++++++++++++++++++
>  1 file changed, 18 insertions(+)
> 
> diff --git a/fs/pstore/ram.c b/fs/pstore/ram.c
> index b1a455f42e93..c200388399fb 100644
> --- a/fs/pstore/ram.c
> +++ b/fs/pstore/ram.c
> @@ -50,6 +50,11 @@ module_param_hw(mem_address, ullong, other, 0400);
>  MODULE_PARM_DESC(mem_address,
>  		"start of reserved RAM used to store oops/panic logs");
>  
> +static char *mem_name;
> +module_param_named(mem_name, mem_name, charp, 0400);
> +MODULE_PARM_DESC(mem_name,
> +		"name of kernel param that holds addr (builtin only)");
> +
>  static ulong mem_size;
>  module_param(mem_size, ulong, 0400);
>  MODULE_PARM_DESC(mem_size,
> @@ -914,6 +919,19 @@ static void __init ramoops_register_dummy(void)
>  {
>  	struct ramoops_platform_data pdata;
>  
> +#ifndef MODULE
> +	/* Only allowed when builtin */

Why only when builtin?

> +	if (mem_name) {
> +		u64 start;
> +		u64 size;
> +
> +		if (memmap_named(mem_name, &start, &size)) {
> +			mem_address = start;
> +			mem_size = size;
> +		}
> +	}
> +#endif

Otherwise this looks good, though I'd prefer some comments about what's
happening here.

(And in retrospect, separately, I probably need to rename "dummy" to
"commandline" or something, since it's gathering valid settings here...)

-- 
Kees Cook