linux-kernel - [tip:x86/mm] x86/mm: Limit mmap() of /dev/mem to valid physical addresses

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Date:   Fri, 20 Oct 2017 05:25:19 -0700
From:   tip-bot for Craig Bergstrom <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     hpa@...or.com, toshi.kani@...com, mcgrof@...e.com,
        linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
        craigb@...gle.com, brgerst@...il.com, peterz@...radead.org,
        tglx@...utronix.de, dvlasenk@...hat.com, bp@...en8.de,
        jpoimboe@...hat.com, luto@...nel.org, mingo@...nel.org,
        akpm@...ux-foundation.org
Subject: [tip:x86/mm] x86/mm: Limit mmap() of /dev/mem to valid physical
 addresses

Commit-ID:  ce56a86e2ade45d052b3228cdfebe913a1ae7381
Gitweb:     https://git.kernel.org/tip/ce56a86e2ade45d052b3228cdfebe913a1ae7381
Author:     Craig Bergstrom <craigb@...gle.com>
AuthorDate: Thu, 19 Oct 2017 13:28:56 -0600
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Fri, 20 Oct 2017 09:48:00 +0200

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

Currently, it is possible to mmap() any offset from /dev/mem.  If a
program mmaps() /dev/mem offsets outside of the addressable limits
of a system, the page table can be corrupted by setting reserved bits.

For example if you mmap() offset 0x0001000000000000 of /dev/mem on an
x86_64 system with a 48-bit bus, the page fault handler will be called
with error_code set to RSVD.  The kernel then crashes with a page table
corruption error.

This change prevents this page table corruption on x86 by refusing
to mmap offsets higher than the highest valid address in the system.

Signed-off-by: Craig Bergstrom <craigb@...gle.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Brian Gerst <brgerst@...il.com>
Cc: Denys Vlasenko <dvlasenk@...hat.com>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Josh Poimboeuf <jpoimboe@...hat.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Luis R. Rodriguez <mcgrof@...e.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Toshi Kani <toshi.kani@...com>
Cc: dsafonov@...tuozzo.com
Cc: kirill.shutemov@...ux.intel.com
Cc: mhocko@...e.com
Cc: oleg@...hat.com
Link: http://lkml.kernel.org/r/20171019192856.39672-1-craigb@google.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 arch/x86/include/asm/io.h |  4 ++++
 arch/x86/mm/mmap.c        | 12 ++++++++++++
 2 files changed, 16 insertions(+)

diff --git a/arch/x86/include/asm/io.h b/arch/x86/include/asm/io.h
index c40a95c..322d25a 100644
--- a/arch/x86/include/asm/io.h
+++ b/arch/x86/include/asm/io.h
@@ -110,6 +110,10 @@ build_mmio_write(__writeq, "q", unsigned long, "r", )
 
 #endif
 
+#define ARCH_HAS_VALID_PHYS_ADDR_RANGE
+extern int valid_phys_addr_range(phys_addr_t addr, size_t size);
+extern int valid_mmap_phys_addr_range(unsigned long pfn, size_t size);
+
 /**
  *	virt_to_phys	-	map virtual addresses to physical
  *	@address: address to remap
diff --git a/arch/x86/mm/mmap.c b/arch/x86/mm/mmap.c
index a996798..320c623 100644
--- a/arch/x86/mm/mmap.c
+++ b/arch/x86/mm/mmap.c
@@ -174,3 +174,15 @@ const char *arch_vma_name(struct vm_area_struct *vma)
 		return "[mpx]";
 	return NULL;
 }
+
+int valid_phys_addr_range(phys_addr_t addr, size_t count)
+{
+	return addr + count <= __pa(high_memory);
+}
+
+int valid_mmap_phys_addr_range(unsigned long pfn, size_t count)
+{
+	phys_addr_t addr = (phys_addr_t)pfn << PAGE_SHIFT;
+
+	return valid_phys_addr_range(addr, count);
+}