pve-edge-kernel/patches/kernel/0186-x86-cpu_entry_area-Prevent-wraparound-in-setup_cpu_e.patch

From 23aa91651cbaf32f10ff75f02c281493ee677dcb Mon Sep 17 00:00:00 2001
From: Thomas Gleixner <[email protected]>
Date: Sat, 23 Dec 2017 19:45:11 +0100
Subject: [PATCH 186/231] x86/cpu_entry_area: Prevent wraparound in
 setup_cpu_entry_area_ptes() on 32bit
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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 <[email protected]>
Signed-off-by: Thomas "Feels stupid" Gleixner <[email protected]>
Tested-by: Borislav Petkov <[email protected]>
(cherry picked from commit f6c4fd506cb626e4346aa81688f255e593a7c5a0)
Signed-off-by: Andy Whitcroft <[email protected]>
Signed-off-by: Kleber Sacilotto de Souza <[email protected]>
(cherry picked from commit 8a21158932b93ed7e72d16683085d55a3a06125e)
Signed-off-by: Fabian Grünbichler <[email protected]>
---
 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