Commit f6c4fd50 authored Dec 23, 2017 by Thomas Gleixner

x86/cpu_entry_area: Prevent wraparound in setup_cpu_entry_area_ptes() on 32bit



The loop which populates the CPU entry area PMDs can wrap around on 32bit
machines when the number of CPUs is small.

It worked wonderful for NR_CPUS=64 for whatever reason and the moron who
wrote that code did not bother to test it with !SMP.

Check for the wraparound to fix it.

Fixes: 92a0f81d ("x86/cpu_entry_area: Move it out of the fixmap")
Reported-by: kernel test robot <fengguang.wu@intel.com>
Signed-off-by: Thomas "Feels stupid" Gleixner <tglx@linutronix.de>
Tested-by: Borislav Petkov <bp@alien8.de>

parent 613e396b

arch/x86/mm/cpu_entry_area.c

+2 −1

Original line number	Diff line number	Diff line
		@@ -122,7 +122,8 @@ static __init void setup_cpu_entry_area_ptes(void)
		start = CPU_ENTRY_AREA_BASE;
		end = start + CPU_ENTRY_AREA_MAP_SIZE;

		for (; start < end; start += PMD_SIZE)
		/* Careful here: start + PMD_SIZE might wrap around */
		for (; start < end && start >= CPU_ENTRY_AREA_BASE; start += PMD_SIZE)
		populate_extra_pte(start);
		#endif
		}