Commit 1151f838 authored May 19, 2017 by Ard Biesheuvel Committed by Will Deacon Jun 01, 2017

arm64: kernel: restrict /dev/mem read() calls to linear region



When running lscpu on an AArch64 system that has SMBIOS version 2.0
tables, it will segfault in the following way:

  Unable to handle kernel paging request at virtual address ffff8000bfff0000
  pgd = ffff8000f9615000
  [ffff8000bfff0000] *pgd=0000000000000000
  Internal error: Oops: 96000007 [#1] PREEMPT SMP
  Modules linked in:
  CPU: 0 PID: 1284 Comm: lscpu Not tainted 4.11.0-rc3+ #103
  Hardware name: QEMU QEMU Virtual Machine, BIOS 0.0.0 02/06/2015
  task: ffff8000fa78e800 task.stack: ffff8000f9780000
  PC is at __arch_copy_to_user+0x90/0x220
  LR is at read_mem+0xcc/0x140

This is caused by the fact that lspci issues a read() on /dev/mem at the
offset where it expects to find the SMBIOS structure array. However, this
region is classified as EFI_RUNTIME_SERVICE_DATA (as per the UEFI spec),
and so it is omitted from the linear mapping.

So let's restrict /dev/mem read/write access to those areas that are
covered by the linear region.

Reported-by: Alexander Graf <agraf@suse.de>
Fixes: 4dffbfc4 ("arm64/efi: mark UEFI reserved regions as MEMBLOCK_NOMAP")
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>

parent db46a72b

arch/arm64/mm/mmap.c

+13 −6

Original line number	Diff line number	Diff line
		@@ -18,6 +18,7 @@

		#include <linux/elf.h>
		#include <linux/fs.h>
		#include <linux/memblock.h>
		#include <linux/mm.h>
		#include <linux/mman.h>
		#include <linux/export.h>
		@@ -103,12 +104,18 @@ void arch_pick_mmap_layout(struct mm_struct *mm)
		*/
		int valid_phys_addr_range(phys_addr_t addr, size_t size)
		{
		if (addr < PHYS_OFFSET)
		return 0;
		if (addr + size > __pa(high_memory - 1) + 1)
		return 0;

		return 1;
		/*
		* Check whether addr is covered by a memory region without the
		* MEMBLOCK_NOMAP attribute, and whether that region covers the
		* entire range. In theory, this could lead to false negatives
		* if the range is covered by distinct but adjacent memory regions
		* that only differ in other attributes. However, few of such
		* attributes have been defined, and it is debatable whether it
		* follows that /dev/mem read() calls should be able traverse
		* such boundaries.
		*/
		return memblock_is_region_memory(addr, size) &&
		memblock_is_map_memory(addr);
		}

		/*

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