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SubjectRe: [PATCH 2/2] riscv: Support CONFIG_STRICT_DEVMEM
Στις 2020-06-17 04:56, Zong Li έγραψε:
> On Tue, Jun 16, 2020 at 8:27 PM Nick Kossifidis <mick@ics.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@sifive.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?

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 ?

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