This is a note to let you know that I've just added the patch titled
arm64: kernel: restrict /dev/mem read() calls to linear region
to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
arm64-kernel-restrict-dev-mem-read-calls-to-linear-region.patch
and it can be found in the queue-4.9 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From foo@baz Mon Apr 9 17:09:24 CEST 2018
From: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
Date: Fri, 19 May 2017 16:42:00 +0100
Subject: arm64: kernel: restrict /dev/mem read() calls to linear region
From: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
[ Upstream commit 1151f838cb626005f4d69bf675dacaaa5ea909d6 ]
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@xxxxxxx>
Fixes: 4dffbfc48d65 ("arm64/efi: mark UEFI reserved regions as MEMBLOCK_NOMAP")
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
Signed-off-by: Will Deacon <will.deacon@xxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/arm64/mm/mmap.c | 19 +++++++++++++------
1 file changed, 13 insertions(+), 6 deletions(-)
--- a/arch/arm64/mm/mmap.c
+++ b/arch/arm64/mm/mmap.c
@@ -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>
@@ -102,12 +103,18 @@ void arch_pick_mmap_layout(struct mm_str
*/
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);
}
/*
Patches currently in stable-queue which might be from ard.biesheuvel@xxxxxxxxxx are
queue-4.9/x86-efi-disable-runtime-services-on-kexec-kernel-if-booted-with-efi-old_map.patch
queue-4.9/arm64-kernel-restrict-dev-mem-read-calls-to-linear-region.patch