From 23aa91651cbaf32f10ff75f02c281493ee677dcb Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Sat, 23 Dec 2017 19:45:11 +0100 Subject: [PATCH 186/242] x86/cpu_entry_area: Prevent wraparound in setup_cpu_entry_area_ptes() on 32bit MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit CVE-2017-5754 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 Signed-off-by: Thomas "Feels stupid" Gleixner Tested-by: Borislav Petkov (cherry picked from commit f6c4fd506cb626e4346aa81688f255e593a7c5a0) Signed-off-by: Andy Whitcroft Signed-off-by: Kleber Sacilotto de Souza (cherry picked from commit 8a21158932b93ed7e72d16683085d55a3a06125e) Signed-off-by: Fabian Grünbichler --- arch/x86/mm/cpu_entry_area.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/arch/x86/mm/cpu_entry_area.c b/arch/x86/mm/cpu_entry_area.c index 21e8b595cbb1..fe814fd5e014 100644 --- 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_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 } -- 2.14.2