linux-kernel - Re: [PATCH v2 06/10] module: introduce MODULE_STATE

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Message-ID: <4a9ca024-fc25-4fe0-94d5-65899b2cec6b@suse.com>
Date: Thu, 23 Jan 2025 15:16:28 +0100
From: Petr Pavlu <petr.pavlu@...e.com>
To: Mike Rapoport <rppt@...nel.org>
Cc: x86@...nel.org, Andrew Morton <akpm@...ux-foundation.org>,
 Andy Lutomirski <luto@...nel.org>,
 Anton Ivanov <anton.ivanov@...bridgegreys.com>,
 Borislav Petkov <bp@...en8.de>, Brendan Higgins <brendan.higgins@...ux.dev>,
 Daniel Gomez <da.gomez@...sung.com>, Daniel Thompson <danielt@...nel.org>,
 Dave Hansen <dave.hansen@...ux.intel.com>, David Gow <davidgow@...gle.com>,
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 Joe Lawrence <joe.lawrence@...hat.com>,
 Johannes Berg <johannes@...solutions.net>,
 Josh Poimboeuf <jpoimboe@...nel.org>,
 "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
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 Luis Chamberlain <mcgrof@...nel.org>, Mark Rutland <mark.rutland@....com>,
 Masami Hiramatsu <mhiramat@...nel.org>, Miroslav Benes <mbenes@...e.cz>,
 "H. Peter Anvin" <hpa@...or.com>, Peter Zijlstra <peterz@...radead.org>,
 Petr Mladek <pmladek@...e.com>, Petr Pavlu <petr.pavlu@...e.com>,
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 linux-modules@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
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Subject: Re: [PATCH v2 06/10] module: introduce MODULE_STATE_GONE

On 1/21/25 10:57, Mike Rapoport wrote:
> In order to use execmem's API for temporal remapping of the memory
> allocated from ROX cache as writable, there is a need to distinguish
> between the state when the module is being formed and the state when it is
> deconstructed and freed so that when module_memory_free() is called from
> error paths during module loading it could restore ROX mappings.
> 
> Replace open coded checks for MODULE_STATE_UNFORMED with a helper
> function module_is_formed() and add a new MODULE_STATE_GONE that will be
> set when the module is deconstructed and freed.

I don't fully follow why this case requires a new module state. My
understanding it that the function load_module() has the necessary
context that after calling layout_and_allocate(), the updated ROX
mappings need to be restored. I would then expect the function to be
appropriately able to unwind this operation in case of an error. It
could be done by having a helper that walks the mappings and calls
execmem_restore_rox(), or if you want to keep it in module_memory_free()
as done in the patch #7 then a flag could be passed down to
module_deallocate() -> free_mod_mem() -> module_memory_free()?

It is at least good that MODULE_STATE_GONE is only set in free_module()
past the sysfs teardown, so it never shows in
/sys/module/<mod>/initstate. Otherwise, this would require teaching kmod
about this state as well.

-- 
Thanks,
Petr