Re: [PATCH 2/2] riscv: Support CONFIG_STRICT_DEVMEM

[Nick Kossifidis]

ÎÏÎÏ 2020-06-17 04:56, Zong Li ÎÎÏÎÏÎ:
> On Tue, Jun 16, 2020 at 8:27 PM Nick Kossifidis <mick@xxxxxxxxxxxx> 
> wrote:
> > ÎÏÎÏ 2020-06-16 10:45, Zong Li ÎÎÏÎÏÎ:
> > > 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@xxxxxxxxxx>
> > > ---
> > >  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?

Sounds good to me, I'll work on this within the week. Do you agree with 
marking the no-map reserved-memory regions as exclusive ?