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

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Date:   Mon, 18 Mar 2019 15:46:53 -0700
From:   <rcampbell@...dia.com>
To:     <linux-kernel@...r.kernel.org>
CC:     Ralph Campbell <rcampbell@...dia.com>,
        Craig Bergstrom <craigb@...gle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Fengguang Wu <fengguang.wu@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Hans Verkuil <hans.verkuil@...co.com>,
        Mauro Carvalho Chehab <mchehab@...pensource.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Sander Eikelenboom <linux@...elenboom.it>,
        Sean Young <sean@...s.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>
Subject: [PATCH 1/1] x86/mm: Fix limit mmap() of /dev/mem to valid physical addresses

From: Ralph Campbell <rcampbell@...dia.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@...dia.com>
Cc: Craig Bergstrom <craigb@...gle.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Boris Ostrovsky <boris.ostrovsky@...cle.com>
Cc: Fengguang Wu <fengguang.wu@...el.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Hans Verkuil <hans.verkuil@...co.com>
Cc: Mauro Carvalho Chehab <mchehab@...pensource.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Sander Eikelenboom <linux@...elenboom.it>
Cc: Sean Young <sean@...s.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...nel.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