linux-kernel - Re: [PATCH] kernel: dma: Make CMA boot parameters __ro_after

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Date:   Sat, 19 Oct 2019 11:07:47 +0530
From:   Shyam Saini <mayhs11saini@...il.com>
To:     Robin Murphy <robin.murphy@....com>
Cc:     Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        Kees Cook <keescook@...omium.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Matthew Wilcox <willy@...radead.org>,
        linux-mm <linux-mm@...ck.org>, iommu@...ts.linux-foundation.org,
        Christopher Lameter <cl@...ux.com>,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH] kernel: dma: Make CMA boot parameters __ro_after_init

Hi Robin,

Sorry for the late reply.


> This parameters are not changed after early boot.
> > By making them __ro_after_init will reduce any attack surface in the
> > kernel.
>
> At a glance, it looks like these are only referenced by a couple of
> __init functions, so couldn't they just be __initdata/__initconst?

yes, You are right it is only used by __init calls and not used anywhere else.

I will resend the updated version.

Thanks a lot for the feedback.


> > Link: https://lwn.net/Articles/676145/
> > Cc: Christoph Hellwig <hch@....de>
> > Cc: Marek Szyprowski <m.szyprowski@...sung.com>
> > Cc: Robin Murphy <robin.murphy@....com>
> > Cc: Matthew Wilcox <willy@...radead.org>
> > Cc: Christopher Lameter <cl@...ux.com>
> > Cc: Kees Cook <keescook@...omium.org>
> > Signed-off-by: Shyam Saini <mayhs11saini@...il.com>
> > ---
> >   kernel/dma/contiguous.c | 8 ++++----
> >   1 file changed, 4 insertions(+), 4 deletions(-)
> >
> > diff --git a/kernel/dma/contiguous.c b/kernel/dma/contiguous.c
> > index 69cfb4345388..1b689b1303cd 100644
> > --- a/kernel/dma/contiguous.c
> > +++ b/kernel/dma/contiguous.c
> > @@ -42,10 +42,10 @@ struct cma *dma_contiguous_default_area;
> >    * Users, who want to set the size of global CMA area for their system
> >    * should use cma= kernel parameter.
> >    */
> > -static const phys_addr_t size_bytes = (phys_addr_t)CMA_SIZE_MBYTES * SZ_1M;
> > -static phys_addr_t size_cmdline = -1;
> > -static phys_addr_t base_cmdline;
> > -static phys_addr_t limit_cmdline;
> > +static const phys_addr_t __ro_after_init size_bytes = (phys_addr_t)CMA_SIZE_MBYTES * SZ_1M;
> > +static phys_addr_t __ro_after_init size_cmdline = -1;
> > +static phys_addr_t __ro_after_init base_cmdline;
> > +static phys_addr_t __ro_after_init limit_cmdline;
> >
> >   static int __init early_cma(char *p)
> >   {
> >