4.14-stable review patch. If anyone has any objections, please let me know.
------------------
From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
commit f6c4fd506cb626e4346aa81688f255e593a7c5a0 upstream.
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: 92a0f81d8957 ("x86/cpu_entry_area: Move it out of the fixmap")
Reported-by: kernel test robot <fengguang.wu@xxxxxxxxx>
Signed-off-by: Thomas "Feels stupid" Gleixner <tglx@xxxxxxxxxxxxx>
Tested-by: Borislav Petkov <bp@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/x86/mm/cpu_entry_area.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
--- a/arch/x86/mm/cpu_entry_area.c
+++ b/arch/x86/mm/cpu_entry_area.c
@@ -122,7 +122,8 @@ static __init void setup_cpu_entry_area_
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
}