take into a/c that kernels >= 5.8.0 removed the pgprot arg from the __vmalloc()

kaiwan · kaiwan · commit 156af8cd1a52 · 2023-04-10T16:17:00.000+05:30
diff --git a/ch9/vmalloc_demo/vmalloc_demo.c b/ch9/vmalloc_demo/vmalloc_demo.c
@@ -23,8 +23,7 @@
 #include <linux/mm.h>
 #include <linux/slab.h>
 #include <linux/vmalloc.h>
-
-#define OURMODNAME   "vmalloc_demo"
+#include <linux/version.h>
 
 MODULE_AUTHOR("Kaiwan N Billimoria");
 MODULE_DESCRIPTION("LKP book:ch9/vmalloc_demo/: simple vmalloc() and friends demo lkm");
@@ -38,7 +37,10 @@ MODULE_PARM_DESC(kvnum, "number of bytes to allocate with the kvmalloc(); (defau
 #define KVN_MIN_BYTES   16
 #define DISP_BYTES      16
 
-static void *vptr_rndm, *vptr_init, *kv, *kvarr, *vrx;
+static void *vptr_rndm, *vptr_init, *kv, *kvarr;
+#if LINUX_VERSION_CODE < KERNEL_VERSION(5, 8, 0)
+static void *vrx;
+#endif
 
 static int vmalloc_try(void)
 {
@@ -51,8 +53,7 @@ static int vmalloc_try(void)
 		pr_warn("vmalloc failed\n");
 		goto err_out1;
 	}
-	pr_info("1. vmalloc():   vptr_rndm = 0x%pK (actual=0x%px)\n",
-		vptr_rndm, vptr_rndm);
+	pr_info("1. vmalloc():   vptr_rndm = 0x%pK (actual=0x%px)\n", vptr_rndm, vptr_rndm);
 	print_hex_dump_bytes(" content: ", DUMP_PREFIX_NONE, vptr_rndm, DISP_BYTES);
 
 	/* 2. vzalloc(); mem contents are set to zeroes */
@@ -61,25 +62,24 @@ static int vmalloc_try(void)
 		pr_warn("vzalloc failed\n");
 		goto err_out2;
 	}
-	pr_info("2. vzalloc():   vptr_init = 0x%pK (actual=0x%px)\n",
-		vptr_init, vptr_init);
+	pr_info("2. vzalloc():   vptr_init = 0x%pK (actual=0x%px)\n", vptr_init, vptr_init);
 	print_hex_dump_bytes(" content: ", DUMP_PREFIX_NONE, vptr_init, DISP_BYTES);
 
-	/* 3. kvmalloc(): allocate 'kvnum' bytes with the kvmalloc(); if kvnum is
-	 * large (enough), this will become a vmalloc() under the hood, else
-	 * it fals back to a kmalloc()
+	/* 3. kvmalloc(): allocate 'kvnum' bytes (5MB by default) with the kvmalloc();
+	 * if kvnum is large (enough), this will become a vmalloc() under the hood,
+	 * else it falls back to a kmalloc()
 	 */
 	kv = kvmalloc(kvnum, GFP_KERNEL);
 	if (!kv) {
 		pr_warn("kvmalloc failed\n");
 		goto err_out3;
 	}
 	pr_info("3. kvmalloc() :        kv = 0x%pK (actual=0x%px)\n"
-			"    (for %d bytes)\n", kv, kv, kvnum);
+		"    (for %d bytes)\n", kv, kv, kvnum);
 	print_hex_dump_bytes(" content: ", DUMP_PREFIX_NONE, kv, KVN_MIN_BYTES);
 
-	/* 4. kcalloc(): allocate an array of 1000 64-bit quantities and zero
-	 * out the memory */
+	/* 4. kcalloc(): allocate an array of 1000 64-bit quantities and zero out the memory
+	 */
 	kvarr = kcalloc(1000, sizeof(u64), GFP_KERNEL);
 	if (!kvarr) {
 		pr_warn("kcalloc failed\n");
@@ -92,7 +92,14 @@ static int vmalloc_try(void)
 #undef WR2ROMEM_BUG
 	/* #define WR2ROMEM_BUG */
 	/* 'Normal' usage: keep this commented out, else
-	 * we will crash! Read the book, Ch 9, for details  :-) */
+	 * we will crash! Read the book, Ch 9, for details  ;-)
+	 */
+	/*
+	 * In 5.8.0, commit 88dca4c 'mm: remove the pgprot argument to __vmalloc'
+	 * has removed the pgprot arg from the __vmalloc(). So, only attempt this
+	 * when we're on kernels < 5.8.0
+	 */
+#if LINUX_VERSION_CODE < KERNEL_VERSION(5, 8, 0)
 	vrx = __vmalloc(42 * PAGE_SIZE, GFP_KERNEL, PAGE_KERNEL_RO);
 	if (!vrx) {
 		pr_warn("__vmalloc failed\n");
@@ -103,13 +110,30 @@ static int vmalloc_try(void)
 	/* Try reading the memory, should be fine */
 	print_hex_dump_bytes(" content: ", DUMP_PREFIX_NONE, vrx, DISP_BYTES);
 #ifdef WR2ROMEM_BUG
-	/* Try writing to the RO memory! We find that the kernel crashes
-	 * (emits an Oops!) */
+	/* Try writing to the RO memory! We should, of course, find that the kernel
+	 * crashes (emits an Oops!)
+	 */
+	pr_info("6. Attempting to now write into a kernel vmalloc-ed region that's RO!\n");
 	*(u64 *) (vrx + 4) = 0xba;
+#endif				/* WR2ROMEM_BUG */
+#else
+/*
+ * Logically, should now use the __vmalloc_node_range() BUT, whoops, it isn't exported!
+ * void *__vmalloc_node_range(unsigned long size, unsigned long align,
+ *            unsigned long start, unsigned long end, gfp_t gfp_mask,
+ *            pgprot_t prot, unsigned long vm_flags, int node,
+ *            const void *caller)
+ */
+	pr_info
+	    ("5. >= 5.8.0 : __vmalloc(): no page prot param; can use __vmalloc_node_range() but it's not exported..");
+	pr_cont(" so, simply skip this case\n");
 #endif
+
 	return 0;		/* success */
+#if LINUX_VERSION_CODE < KERNEL_VERSION(5, 8, 0)
  err_out5:
 	vfree(kvarr);
+#endif
  err_out4:
 	vfree(kv);
  err_out3:
@@ -123,7 +147,8 @@ static int vmalloc_try(void)
 static int __init vmalloc_demo_init(void)
 {
 	if (kvnum < KVN_MIN_BYTES) {
-		pr_info("kvnum must be >= %d bytes (curr it's %d bytes)\n", KVN_MIN_BYTES, kvnum);
+		pr_info("kvnum must be >= %d bytes (curr it's %d bytes)\n", KVN_MIN_BYTES,
+			kvnum);
 		return -EINVAL;
 	}
 	pr_info("inserted\n");
@@ -133,7 +158,9 @@ static int __init vmalloc_demo_init(void)
 
 static void __exit vmalloc_demo_exit(void)
 {
+#if LINUX_VERSION_CODE < KERNEL_VERSION(5, 8, 0)
 	vfree(vrx);
+#endif
 	kvfree(kvarr);
 	kvfree(kv);
 	vfree(vptr_init);
