Unverified Commit 527701ed authored by Palmer Dabbelt's avatar Palmer Dabbelt
Browse files

lib: Add a generic version of devmem_is_allowed() 



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: default avatarLuis Chamberlain <mcgrof@kernel.org>
Signed-off-by: default avatarPalmer Dabbelt <palmerdabbelt@google.com>
parent bbf5c979

include/asm-generic/io.h

+4 −0
Original line number Diff line number Diff line
@@ -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 */

lib/Kconfig

+3 −0
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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

lib/Kconfig.debug

+1 −1
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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

lib/Makefile

+2 −0
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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

lib/devmem_is_allowed.c

0 → 100644
+27 −0
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// 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;

}