[Crash-utility] [PATCH] Fix memory driver module build with kernel 5.8+

[Petr Tesarik]

Kernel commit fe557319aa06c23cffc9346000f119547e0f289a renamed
probe_kernel_{read,write} to copy_{from,to}_kernel_nofault.

Additionally, commit 0493cb086353e786be56010780a0b7025b5db34c
unexported probe_kernel_write(), so writing kernel memory is
no longer possible from a module.

I have renamed the functions in source, but I'm also adding wrappers to
allow building the module with older kernel versions.

Without this patch, build with kernel 5.8 and later fails:

kbuild/default/crash.c: In function 'crash_write':
kbuild/default/crash.c:189:12: error: implicit declaration of function 'probe_kernel_write'; did you mean 'kernel_write'? [-Werror=implicit-function-declaration]
  189 |        if (probe_kernel_write(vaddr, buffer, count)) {
      |            ^~~~~~~~~~~~~~~~~~
      |            kernel_write
kbuild/default/crash.c: In function 'crash_read':
kbuild/default/crash.c:225:13: error: implicit declaration of function 'probe_kernel_read'; did you mean 'kernel_read'? [-Werror=implicit-function-declaration]
  225 |         if (probe_kernel_read(buffer, vaddr, count)) {
      |             ^~~~~~~~~~~~~~~~~
      |             kernel_read

Signed-off-by: Petr Tesarik <ptesarik at suse.com>

---
 memory_driver/crash.c |   27 +++++++++++++++++++++++++--
 1 file changed, 25 insertions(+), 2 deletions(-)

--- a/memory_driver/crash.c
+++ b/memory_driver/crash.c
@@ -25,6 +25,7 @@
  *****************************************************************************/
 
 #include <linux/module.h>
+#include <linux/version.h>
 #include <linux/types.h>
 #include <linux/miscdevice.h>
 #include <linux/init.h>
@@ -37,6 +38,22 @@
 
 extern int page_is_ram(unsigned long);
 
+#if LINUX_VERSION_CODE < KERNEL_VERSION(5, 8, 0)
+
+#define CAN_WRITE_KERNEL	1
+
+static inline long copy_from_kernel_nofault(void *dst, const void *src, size_t size)
+{
+	return probe_kernel_read(dst, src, size);
+}
+
+static inline long copy_to_kernel_nofault(void *dst, const void *src, size_t size)
+{
+	return probe_kernel_write(dst, src, size);
+}
+
+#endif
+
 #ifdef CONFIG_S390
 /*
  * For swapped prefix pages get bounce buffer using xlate_dev_mem_ptr()
@@ -160,6 +177,8 @@ crash_llseek(struct file * file, loff_t
 	}
 }
 
+#ifdef CAN_WRITE_KERNEL
+
 static ssize_t
 crash_write(struct file *file, const char *buf, size_t count, loff_t *poff)
 {
@@ -186,7 +205,7 @@ crash_write(struct file *file, const cha
                return -EFAULT;
        }
 
-       if (probe_kernel_write(vaddr, buffer, count)) {
+       if (copy_to_kernel_nofault(vaddr, buffer, count)) {
                unmap_virtual(page);
                return -EFAULT;
        }
@@ -197,6 +216,8 @@ crash_write(struct file *file, const cha
        return written;
 }
 
+#endif
+
 /*
  *  Determine the page address for an address offset value,
  *  get a virtual address for it, and copy it out.
@@ -222,7 +243,7 @@ crash_read(struct file *file, char *buf,
 	 * Use bounce buffer to bypass the CONFIG_HARDENED_USERCOPY
 	 * kernel text restriction.
 	 */
-        if (probe_kernel_read(buffer, vaddr, count)) {
+        if (copy_from_kernel_nofault(buffer, vaddr, count)) {
                 unmap_virtual(page);
                 return -EFAULT;
         }
@@ -294,7 +315,9 @@ static struct file_operations crash_fops
 	.owner = THIS_MODULE,
 	.llseek = crash_llseek,
 	.read = crash_read,
+#ifdef CAN_WRITE_KERNEL
 	.write = crash_write,
+#endif
 	.unlocked_ioctl = crash_ioctl,
 	.open = crash_open,
 	.release = crash_release,
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