release/5.2.22/powerpc-kasan-Fix-parallel-loading-of-modules.patch

From 2745883e9b34aa891fba20253334d99b5b7c1bc1 Mon Sep 17 00:00:00 2001
From: Christophe Leroy <christophe.leroy@c-s.fr>
Date: Fri, 9 Aug 2019 14:58:09 +0000
Subject: [PATCH] powerpc/kasan: Fix parallel loading of modules.

commit 45ff3c55958542c3b76075d59741297b8cb31cbb upstream.

Parallel loading of modules may lead to bad setup of shadow page table
entries.

First, lets align modules so that two modules never share the same
shadow page.

Second, ensure that two modules cannot allocate two page tables for
the same PMD entry at the same time. This is done by using
init_mm.page_table_lock in the same way as __pte_alloc_kernel()

Fixes: 2edb16efc899 ("powerpc/32: Add KASAN support")
Cc: stable@vger.kernel.org # v5.2+
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/c97284f912128cbc3f2fe09d68e90e65fb3e6026.1565361876.git.christophe.leroy@c-s.fr
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>

diff --git a/arch/powerpc/mm/kasan/kasan_init_32.c b/arch/powerpc/mm/kasan/kasan_init_32.c
index 74f4555a62ba..3282f8a2aecc 100644
--- a/arch/powerpc/mm/kasan/kasan_init_32.c
+++ b/arch/powerpc/mm/kasan/kasan_init_32.c
@@ -5,6 +5,7 @@
 #include <linux/kasan.h>
 #include <linux/printk.h>
 #include <linux/memblock.h>
+#include <linux/moduleloader.h>
 #include <linux/sched/task.h>
 #include <linux/vmalloc.h>
 #include <asm/pgalloc.h>
@@ -46,7 +47,19 @@ static int __ref kasan_init_shadow_page_tables(unsigned long k_start, unsigned l
 			kasan_populate_pte(new, PAGE_READONLY);
 		else
 			kasan_populate_pte(new, PAGE_KERNEL_RO);
-		pmd_populate_kernel(&init_mm, pmd, new);
+
+		smp_wmb(); /* See comment in __pte_alloc */
+
+		spin_lock(&init_mm.page_table_lock);
+			/* Has another populated it ? */
+		if (likely((void *)pmd_page_vaddr(*pmd) == kasan_early_shadow_pte)) {
+			pmd_populate_kernel(&init_mm, pmd, new);
+			new = NULL;
+		}
+		spin_unlock(&init_mm.page_table_lock);
+
+		if (new && slab_is_available())
+			pte_free_kernel(&init_mm, new);
 	}
 	return 0;
 }
@@ -137,7 +150,11 @@ void __init kasan_init(void)
 #ifdef CONFIG_MODULES
 void *module_alloc(unsigned long size)
 {
-	void *base = vmalloc_exec(size);
+	void *base;
+
+	base = __vmalloc_node_range(size, MODULE_ALIGN, VMALLOC_START, VMALLOC_END,
+				    GFP_KERNEL, PAGE_KERNEL_EXEC, VM_FLUSH_RESET_PERMS,
+				    NUMA_NO_NODE, __builtin_return_address(0));
 
 	if (!base)
 		return NULL;
-- 
2.7.4