linux-kernel - Re: [PATCH 2/2] riscv: Support CONFIG_STRICT

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Date:   Wed, 17 Jun 2020 09:56:04 +0800
From:   Zong Li <zong.li@...ive.com>
To:     Nick Kossifidis <mick@....forth.gr>
Cc:     Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org List" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] riscv: Support CONFIG_STRICT_DEVMEM

On Tue, Jun 16, 2020 at 8:27 PM Nick Kossifidis <mick@....forth.gr> wrote:
>
> Στις 2020-06-16 10:45, Zong Li έγραψε:
> > Implement the 'devmem_is_allowed()' interface for RISC-V, like some of
> > other architectures have done. It will be called from
> > range_is_allowed()
> > when userpsace attempts to access /dev/mem.
> >
> > Access to exclusive IOMEM and kernel RAM is denied unless
> > CONFIG_STRICT_DEVMEM is set to 'n'.
> >
> > Test it by devmem, the result as follows:
> >
> >  - CONFIG_STRICT_DEVMEM=y
> >       $ devmem 0x10010000
> >       0x00000000
> >       $ devmem 0x80200000
> >       0x0000106F
> >
> >  - CONFIG_STRICT_DEVMEM is not set
> >       $ devmem 0x10010000
> >       devmem: mmap: Operation not permitted
> >       $ devmem 0x80200000
> >       devmem: mmap: Operation not permitted
> >
> > Signed-off-by: Zong Li <zong.li@...ive.com>
> > ---
> >  arch/riscv/Kconfig          |  1 +
> >  arch/riscv/include/asm/io.h |  2 ++
> >  arch/riscv/mm/init.c        | 19 +++++++++++++++++++
> >  3 files changed, 22 insertions(+)
> >
> > diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> > index 128192e14ff2..ffd7841ede4c 100644
> > --- a/arch/riscv/Kconfig
> > +++ b/arch/riscv/Kconfig
> > @@ -16,6 +16,7 @@ config RISCV
> >       select ARCH_HAS_BINFMT_FLAT
> >       select ARCH_HAS_DEBUG_VIRTUAL if MMU
> >       select ARCH_HAS_DEBUG_WX
> > +     select ARCH_HAS_DEVMEM_IS_ALLOWED
> >       select ARCH_HAS_GCOV_PROFILE_ALL
> >       select ARCH_HAS_GIGANTIC_PAGE
> >       select ARCH_HAS_MMIOWB
> > diff --git a/arch/riscv/include/asm/io.h b/arch/riscv/include/asm/io.h
> > index 3835c3295dc5..04ac65ab93ce 100644
> > --- a/arch/riscv/include/asm/io.h
> > +++ b/arch/riscv/include/asm/io.h
> > @@ -147,4 +147,6 @@ __io_writes_outs(outs, u64, q, __io_pbr(),
> > __io_paw())
> >
> >  #include <asm-generic/io.h>
> >
> > +extern int devmem_is_allowed(unsigned long pfn);
> > +
> >  #endif /* _ASM_RISCV_IO_H */
> > diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> > index bbe816e03b2f..5e7e61519acc 100644
> > --- a/arch/riscv/mm/init.c
> > +++ b/arch/riscv/mm/init.c
> > @@ -517,6 +517,25 @@ void mark_rodata_ro(void)
> >  }
> >  #endif
> >
> > +#ifdef CONFIG_STRICT_DEVMEM
> > +#include <linux/ioport.h>
> > +/*
> > + * devmem_is_allowed() checks to see if /dev/mem access to a certain
> > address
> > + * is valid. The argument is a physical page number.
> > + *
> > + * Disallow access to system RAM as well as device-exclusive MMIO
> > regions.
> > + * This effectively disable read()/write() on /dev/mem.
> > + */
> > +int devmem_is_allowed(unsigned long pfn)
> > +{
> > +     if (iomem_is_exclusive(pfn << PAGE_SHIFT))
> > +             return 0;
> > +     if (!page_is_ram(pfn))
> > +             return 1;
> > +     return 0;
> > +}
> > +#endif
> > +
> >  void __init resource_init(void)
> >  {
> >       struct memblock_region *region;
>
> This shouldn't be part of /mm/init.c, it has nothing to do with memory
> initialization, I suggest we move it to another file like mmap.c on

Let me move it, thanks.

> arm/arm64. Also before using iomem_is_exclusive we should probably also
> mark any reserved regions with the no-map attribute as busy|exclusive,
> reserved-memory regions are not necessarily part of the main memory so
> the page_is_ram check may pass and iomem_is_exclusive won't do any good.

What do you think if we mark the reserved region in
kdump_resource_init, and change the kdump_resource_init to a more
generic name for initializing resources?