Hi Palmer,
On Thu, Jul 09, 2020 at 01:05:48PM -0700, Palmer Dabbelt wrote:
> From: Palmer Dabbelt <palmerdabbelt@xxxxxxxxxx>
>
> As part of adding support for STRICT_DEVMEM to the RISC-V port, Zong
> provided a devmem_is_allowed() implementation that's exactly the same as
> all the others I checked. Instead I'm adding a generic version, which
> will soon be used.
>
> Signed-off-by: Palmer Dabbelt <palmerdabbelt@xxxxxxxxxx>
> ---
> include/asm-generic/io.h | 4 ++++
> lib/Kconfig | 4 ++++
> lib/Makefile | 2 ++
> lib/devmem_is_allowed.c | 27 +++++++++++++++++++++++++++
> 4 files changed, 37 insertions(+)
> create mode 100644 lib/devmem_is_allowed.c
>
> diff --git a/include/asm-generic/io.h b/include/asm-generic/io.h
> index 8b1e020e9a03..69e3db65fba0 100644
> --- a/include/asm-generic/io.h
> +++ b/include/asm-generic/io.h
> @@ -1122,6 +1122,10 @@ static inline void memcpy_toio(volatile void __iomem *addr, const void *buffer,
> }
> #endif
>
> +#ifndef CONFIG_GENERIC_DEVMEM_IS_ALLOWED
> +extern int devmem_is_allowed(unsigned long pfn);
> +#endif
> +
> #endif /* __KERNEL__ */
>
> #endif /* __ASM_GENERIC_IO_H */
> diff --git a/lib/Kconfig b/lib/Kconfig
> index df3f3da95990..3b1b6481e073 100644
> --- a/lib/Kconfig
> +++ b/lib/Kconfig
> @@ -676,3 +676,7 @@ config GENERIC_LIB_CMPDI2
>
> config GENERIC_LIB_UCMPDI2
> bool
> +
> +config GENERIC_LIB_DEVMEM_IS_ALLOWED
> + bool
> + select ARCH_HAS_DEVMEM_IS_ALLOWED
This seems to work the other way around from the usual Kconfig chains.
In the most cases ARCH_HAS_SOMETHING selects GENERIC_SOMETHING.
I believe nicer way would be to make
config STRICT_DEVMEM
bool "Filter access to /dev/mem"
depends on MMU && DEVMEM
depends on ARCH_HAS_DEVMEM_IS_ALLOWED || GENERIC_LIB_DEVMEM_IS_ALLOWED
config GENERIC_LIB_DEVMEM_IS_ALLOWED
bool
and then s/select ARCH_HAS_DEVMEM_IS_ALLOWED/select GENERIC_LIB_DEVMEM_IS_ALLOWED/
in the arch Kconfigs and drop ARCH_HAS_DEVMEM_IS_ALLOWED in the end.
> diff --git a/lib/Makefile b/lib/Makefile
> index b1c42c10073b..554ef14f9be5 100644
> --- a/lib/Makefile
> +++ b/lib/Makefile
> @@ -318,3 +318,5 @@ obj-$(CONFIG_OBJAGG) += objagg.o
> # KUnit tests
> obj-$(CONFIG_LIST_KUNIT_TEST) += list-test.o
> obj-$(CONFIG_LINEAR_RANGES_TEST) += test_linear_ranges.o
> +
> +obj-$(CONFIG_GENERIC_LIB_DEVMEM_IS_ALLOWED) += devmem_is_allowed.o
> diff --git a/lib/devmem_is_allowed.c b/lib/devmem_is_allowed.c
> new file mode 100644
> index 000000000000..c0d67c541849
> --- /dev/null
> +++ b/lib/devmem_is_allowed.c
> @@ -0,0 +1,27 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * A generic version of devmem_is_allowed.
> + *
> + * Based on arch/arm64/mm/mmap.c
> + *
> + * Copyright (C) 2020 Google, Inc.
> + * Copyright (C) 2012 ARM Ltd.
> + */
> +
> +#include <linux/mm.h>
> +#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. We mimic x86 here by
> + * disallowing 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;
> +}
> --
> 2.27.0.383.g050319c2ae-goog
>
--
Sincerely yours,
Mike.
