[PATCH 1/1] x86/mm: Fix limit mmap() of /dev/mem to valid physical addresses

rcampbell
2019-03-18T22:47:25Z

From: Ralph Campbell <rcampbell@nvidia.com>

If CONFIG_DEBUG_VIRTUAL is enabled, a read or write to /dev/mem can
trigger a VIRTUAL_BUG_ON() depending on the value of high_memory.
For example:

read_mem()
valid_phys_addr_range(p=401f1550, count=8)
__pa(high_memory)
__phys_addr(x=ffffc88000000000)
// __START_KERNEL_map = ffffffff80000000
// y = ffffc88000000000 - ffffffff80000000
VIRTUAL_BUG_ON(phys_addr_valid(400000000000))
// boot_cpu_data.x86_phys_bits=46

Since by design high_memory is outside the range of valid physical
addresses, use the non-error checking version __pa_nodebug(high_memory).

Fixes: be62a32044061cb4a3b70a10598e093f1319102e ("x86/mm: Limit mmap() of
/dev/mem to valid physical addresses")

Signed-off-by: Ralph Campbell <rcampbell@nvidia.com>
Cc: Craig Bergstrom <craigb@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Fengguang Wu <fengguang.wu@intel.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Hans Verkuil <hans.verkuil@cisco.com>
Cc: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sander Eikelenboom <linux@eikelenboom.it>
Cc: Sean Young <sean@mess.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
---
arch/x86/mm/mmap.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/mm/mmap.c b/arch/x86/mm/mmap.c
index db3165714521..196bed43d5e6 100644
--- a/arch/x86/mm/mmap.c
+++ b/arch/x86/mm/mmap.c
@@ -230,7 +230,7 @@ bool mmap_address_hint_valid(unsigned long addr, unsigned long len)
/* Can we access it for direct reading/writing? Must be RAM: */
int valid_phys_addr_range(phys_addr_t addr, size_t count)
{
- return addr + count <= __pa(high_memory);
+ return addr + count <= __pa_nodebug(high_memory);
}

/* Can we access it through mmap? Must be a valid physical address: */
--
2.20.1