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

[Russell King - ARM Linux]

On Wed, Apr 12, 2017 at 10:33:43AM +0200, Domenico Andreoli wrote:
> On Wed, Apr 12, 2017 at 09:26:06AM +0100, Ard Biesheuvel wrote:
> > 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 at suse.de>
> > Fixes: 4dffbfc48d65 ("arm64/efi: mark UEFI reserved regions as MEMBLOCK_NOMAP")
> > Signed-off-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>
> > ---
> >  arch/arm64/mm/mmap.c | 9 +++------
> >  1 file changed, 3 insertions(+), 6 deletions(-)
> > 
> > diff --git a/arch/arm64/mm/mmap.c b/arch/arm64/mm/mmap.c
> > index 7b0d55756eb1..2956240d17d7 100644
> > --- 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>
> > @@ -103,12 +104,8 @@ 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;
> > +	return memblock_is_map_memory(addr) &&
> > +	       memblock_is_map_memory(addr + size - 1);
> >  }
> >  
> >  /*
> 
> Does arch/arm/mm/mmap.c need the same treatment?

high_memory is supposed to be the virtual address of the end of the
linearly mapped region.  ARM conforms to that.

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