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lib: Add a generic version of devmem_is_allowed()

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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.

Reviewed-by: Luis Chamberlain <mcgrof@kernel.org>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>
This commit is contained in:
Palmer Dabbelt 2020-07-09 11:43:21 -07:00
parent bbf5c97901
commit 527701eda5
No known key found for this signature in database
GPG Key ID: 2E1319F35FBB1889
5 changed files with 37 additions and 1 deletions
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4
include/asm-generic/io.h
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@ -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 */

3
lib/Kconfig
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@ -681,6 +681,9 @@ config GENERIC_LIB_CMPDI2
config GENERIC_LIB_UCMPDI2
bool
config GENERIC_LIB_DEVMEM_IS_ALLOWED
bool
config PLDMFW
bool
default n

2
lib/Kconfig.debug
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@ -1626,7 +1626,7 @@ config ARCH_HAS_DEVMEM_IS_ALLOWED
config STRICT_DEVMEM
bool "Filter access to /dev/mem"
depends on MMU && DEVMEM
depends on ARCH_HAS_DEVMEM_IS_ALLOWED
depends on ARCH_HAS_DEVMEM_IS_ALLOWED || GENERIC_LIB_DEVMEM_IS_ALLOWED
default y if PPC || X86 || ARM64
help
If this option is disabled, you allow userspace (root) access to all

2
lib/Makefile
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@ -348,3 +348,5 @@ obj-$(CONFIG_PLDMFW) += pldmfw/
obj-$(CONFIG_LIST_KUNIT_TEST) += list-test.o
obj-$(CONFIG_LINEAR_RANGES_TEST) += test_linear_ranges.o
obj-$(CONFIG_BITS_TEST) += test_bits.o
obj-$(CONFIG_GENERIC_LIB_DEVMEM_IS_ALLOWED) += devmem_is_allowed.o

27
lib/devmem_is_allowed.c Normal file
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@ -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;
}