linux-kernel - Re: [PATCH v5 7/8] execmem: add support for cache of large ROX pages

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Message-ID: <ZwjXz0dz-RldVNx0@infradead.org>
Date: Fri, 11 Oct 2024 00:46:23 -0700
From: Christoph Hellwig <hch@...radead.org>
To: Mike Rapoport <rppt@...nel.org>
Cc: Christoph Hellwig <hch@...radead.org>,
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Subject: Re: [PATCH v5 7/8] execmem: add support for cache of large ROX pages

On Thu, Oct 10, 2024 at 03:57:33PM +0300, Mike Rapoport wrote:
> On Wed, Oct 09, 2024 at 11:58:33PM -0700, Christoph Hellwig wrote:
> > On Wed, Oct 09, 2024 at 09:08:15PM +0300, Mike Rapoport wrote:
> > >  /**
> > >   * struct execmem_info - architecture parameters for code allocations
> > > + * @fill_trapping_insns: set memory to contain instructions that will trap
> > >   * @ranges: array of parameter sets defining architecture specific
> > >   * parameters for executable memory allocations. The ranges that are not
> > >   * explicitly initialized by an architecture use parameters defined for
> > >   * @EXECMEM_DEFAULT.
> > >   */
> > >  struct execmem_info {
> > > +	void (*fill_trapping_insns)(void *ptr, size_t size, bool writable);
> > >  	struct execmem_range	ranges[EXECMEM_TYPE_MAX];
> > 
> > Why is the filler an indirect function call and not an architecture
> > hook?
> 
> The idea is to keep everything together and have execmem_info describe all
> that architecture needs. 

But why?  That's pretty different from our normal style of arch hooks,
and introduces an indirect call in a security sensitive area.