x86/mm: Don't exceed the valid physical address space

Ralph Campbell · KAGA-KOKO · commit 92c77f7c4d5d · 2019-03-28T14:13:51.000+01:00
valid_phys_addr_range() is used to sanity check the physical address range of an operation, e.g., access to /dev/mem. It uses __pa(high_memory) internally. If memory is populated at the end of the physical address space, then __pa(high_memory) is outside of the physical address space because: high_memory = (void *)__va(max_pfn * PAGE_SIZE - 1) + 1; For the comparison in valid_phys_addr_range() this is not an issue, but if CONFIG_DEBUG_VIRTUAL is enabled, __pa() maps to __phys_addr(), which verifies that the resulting physical address is within the valid physical address space of the CPU. So in the case that memory is populated at the end of the physical address space, this is not true and triggers a VIRTUAL_BUG_ON(). Use __pa(high_memory - 1) to prevent the conversion from going beyond the end of valid physical addresses. Fixes: be62a32 ("x86/mm: Limit mmap() of /dev/mem to valid physical addresses") Signed-off-by: Ralph Campbell <rcampbell@nvidia.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> 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> Link: https://lkml.kernel.org/r/20190326001817.15413-2-rcampbell@nvidia.com
diff --git 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 - 1 <= __pa(high_memory - 1);
 }
 
 /* Can we access it through mmap? Must be a valid physical address: */

Original file line number	Diff line number	Diff line change
`@@ -230,7 +230,7 @@ bool mmap_address_hint_valid(unsigned long addr, unsigned long len)`
`230`	`230`	`/* Can we access it for direct reading/writing? Must be RAM: */`
`231`	`231`	`int valid_phys_addr_range(phys_addr_t addr, size_t count)`
`232`	`232`	`{`
`233`		`- return addr + count <= __pa(high_memory);`
	`233`	`+ return addr + count - 1 <= __pa(high_memory - 1);`
`234`	`234`	`}`
`235`	`235`
`236`	`236`	`/* Can we access it through mmap? Must be a valid physical address: */`