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%3Ba=su...
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@vger.kernel.org know about it.
From foo@baz Mon Apr 9 17:09:24 CEST 2018
From: Ard Biesheuvel ard.biesheuvel@linaro.org 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@linaro.org
[ 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@suse.de Fixes: 4dffbfc48d65 ("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 Signed-off-by: Sasha Levin alexander.levin@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- 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@linaro.org 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