linux-kernel - Re: [PATCH v3 6/9] module: switch to execmem API for remapping as RW and restoring ROX

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Message-ID: <Z5iq2GJKIdlB9APM@kernel.org>
Date: Tue, 28 Jan 2025 12:00:56 +0200
From: Mike Rapoport <rppt@...nel.org>
To: Petr Pavlu <petr.pavlu@...e.com>
Cc: x86@...nel.org, Andrew Morton <akpm@...ux-foundation.org>,
	Andy Lutomirski <luto@...nel.org>,
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	Borislav Petkov <bp@...en8.de>,
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	Daniel Thompson <danielt@...nel.org>,
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Subject: Re: [PATCH v3 6/9] module: switch to execmem API for remapping as RW
 and restoring ROX

On Mon, Jan 27, 2025 at 01:50:31PM +0100, Petr Pavlu wrote:
> On 1/26/25 08:47, Mike Rapoport wrote:
> > From: "Mike Rapoport (Microsoft)" <rppt@...nel.org>
> > 
> > Instead of using writable copy for module text sections, temporarily remap
> > the memory allocated from execmem's ROX cache as writable and restore its
> > ROX permissions after the module is formed.
> > 
> > This will allow removing nasty games with writable copy in alternatives
> > patching on x86.
> > 
> > Signed-off-by: Mike Rapoport (Microsoft) <rppt@...nel.org>
> 
> [...]
> 
> > +static void module_memory_restore_rox(struct module *mod)
> > +{
> > +	for_class_mod_mem_type(type, text) {
> > +		struct module_memory *mem = &mod->mem[type];
> > +
> > +		if (mem->is_rox)
> > +			execmem_restore_rox(mem->base, mem->size);
> > +	}
> > +}
> > +
> 
> Can the execmem_restore_rox() call here fail? I realize that there isn't
> much that the module loader can do if that happens, but should it be
> perhaps logged as a warning?

It won't fail at this point. set_memory APIs may fail if they need to split
a large page and could not allocate a new page table, but here all the
splits were already done at module_memory_alloc() time.
 
> -- 
> Thanks,
> Petr

-- 
Sincerely yours,
Mike.