From: Josh Poimboeuf <jpoimboe@kernel.org>
To: Luis Chamberlain <mcgrof@kernel.org>
Cc: Masahiro Yamada <masahiroy@kernel.org>,
Petr Mladek <pmladek@suse.com>, Song Liu <song@kernel.org>,
patches@lists.linux.dev, linux-modules@vger.kernel.org,
live-patching@vger.kernel.org, linux-kbuild@vger.kernel.org
Subject: Re: mod->klp set on copy ok ?
Date: Fri, 17 Mar 2023 16:31:22 -0700 [thread overview]
Message-ID: <20230317233122.4vsewgrb3nq574fs@treble> (raw)
In-Reply-To: <ZBS42Lid+CX0h0fk@bombadil.infradead.org>
On Fri, Mar 17, 2023 at 12:00:40PM -0700, Luis Chamberlain wrote:
> > I dug into that code years ago, and the above sounds right.
> >
> > The .ko file has a .gnu.linkonce.this_module section whose data is just
> > the original "struct module __this_module" which is created by the
> > module build (from foo.mod.c).
> >
> > At the beginning of the finit_module() syscall, the .ko file's ELF
> > sections get copied (and optionally decompressed) into kernel memory.
> > Then 'mod' just points to the copied __this_module struct.
> >
> > Then mod->klp (and possibly mod->taint) get set.
> >
> > Then in layout_and_allocate(), that 'mod' gets memcpy'd into the second
> > (and final) in-kernel copy of 'struct module':
> >
> > if (shdr->sh_type != SHT_NOBITS)
> > memcpy(dest, (void *)shdr->sh_addr, shdr->sh_size);
> > /* Update sh_addr to point to copy in image. */
> > shdr->sh_addr = (unsigned long)dest;
> >
> > I suspect you don't see the size changing when you add to 'struct
> > module' because it's ____cacheline_aligned.
> >
> > It's all rather obtuse, but working as designed as far as I can tell.
>
> Ah, well it is beyond a ____cacheline_aligned issue! It would seem our build
> system does not incur a full re-build of $foo.mod.c if the size of struct module
> changes. Doing a full rebuild does get the right drift size change in
> struct module:
Ah, ok. It sounds like build dependencies are broken for *.mod.c.
The added validations in the patch look reasonable, though the broken
build dependencies should also get fixed.
--
Josh
prev parent reply other threads:[~2023-03-17 23:31 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <CAB=NE6Vo4AXVrn1GPEoZWVF3NkXRoPwWOuUEJqJ35S9VMGTM2Q@mail.gmail.com>
[not found] ` <ZA8NBuXbVP+PRPp0@alley>
2023-03-16 21:50 ` mod->klp set on copy ok ? Luis Chamberlain
2023-03-17 16:16 ` Josh Poimboeuf
2023-03-17 19:00 ` Luis Chamberlain
2023-03-17 23:31 ` Josh Poimboeuf [this message]
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