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

[HAGIO KAZUHITO(萩尾 一仁)]

-----Original Message-----
> 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>

Thank you for catching this, the patch looks good to me.

Acked-by: Kazuhito Hagio <k-hagio-ab at nec.com>

additionally, I think we should update the version number of this module.
I'll add this change when applying, is it ok?  Lianbo, Bhupesh.

-#define CRASH_VERSION   "1.4"
+#define CRASH_VERSION   "1.5"

Anyway, please wait for another ack.

Thanks,
Kazu

> 
> ---
>  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,