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Liang Wang
854f32648b
The physical address may exceed 32 bits on 32-bit systems with more than 32 bits of physcial address. Use PFN_PHYS() in devmem_is_allowed(), or the physical address may overflow and be truncated. We found this bug when mapping a high addresses through devmem tool, when CONFIG_STRICT_DEVMEM is enabled on the ARM with ARM_LPAE and devmem is used to map a high address that is not in the iomem address range, an unexpected error indicating no permission is returned. This bug was initially introduced from v2.6.37, and the function was moved to lib in v5.11. Link: https://lkml.kernel.org/r/[email protected] Fixes:087aaffcdf("ARM: implement CONFIG_STRICT_DEVMEM by disabling access to RAM via /dev/mem") Fixes:527701eda5("lib: Add a generic version of devmem_is_allowed()") Signed-off-by: Liang Wang <[email protected]> Reviewed-by: Luis Chamberlain <[email protected]> Cc: Palmer Dabbelt <[email protected]> Cc: Greg Kroah-Hartman <[email protected]> Cc: Russell King <[email protected]> Cc: Liang Wang <[email protected]> Cc: Xiaoming Ni <[email protected]> Cc: Kefeng Wang <[email protected]> Cc: <[email protected]> [2.6.37+] Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>
28 lines
683 B
C
28 lines
683 B
C
// SPDX-License-Identifier: GPL-2.0-only
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/*
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* A generic version of devmem_is_allowed.
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*
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* Based on arch/arm64/mm/mmap.c
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*
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* Copyright (C) 2020 Google, Inc.
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* Copyright (C) 2012 ARM Ltd.
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*/
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#include <linux/mm.h>
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#include <linux/ioport.h>
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/*
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* devmem_is_allowed() checks to see if /dev/mem access to a certain address
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* is valid. The argument is a physical page number. We mimic x86 here by
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* disallowing access to system RAM as well as device-exclusive MMIO regions.
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* This effectively disable read()/write() on /dev/mem.
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*/
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int devmem_is_allowed(unsigned long pfn)
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{
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if (iomem_is_exclusive(PFN_PHYS(pfn)))
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return 0;
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if (!page_is_ram(pfn))
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return 1;
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return 0;
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}
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