Hi Petr,
Thanks for the patch. I have some nitpicks, please see inline:
On Fri, Sep 4, 2020 at 7:24 PM Petr Tesarik <ptesarik@xxxxxxx> wrote:
>
> 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@xxxxxxxx>
>
> ---
> 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
Hmmm.. I have no strong opinion about this, but can I suggest using a
simple variable instead of a macro.
Something like a 'unsigned int version_info':
unsigned int version_info = LINUX_VERSION_CODE;
and then perform the check in the code at run time against the 'version_info'.
To me, it seems more portable in future, as we are seeing such issues
with newer kernels (due to function name renaming/deprecation).
Another minor nitpick: Can I suggest adding a comment to this code leg
- this can help while backporting patches to distributions (which
still work with older kernel versions) - as it helps making a better
informed decision while backporting the patch.
> +
> +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,
> --
> Crash-utility mailing list
> Crash-utility@xxxxxxxxxx
> https://www.redhat.com/mailman/listinfo/crash-utility
With the above points addressed, please feel free to add:
Acked-by: Bhupesh Sharma <bhsharma@xxxxxxxxxx>
Thanks.
--
Crash-utility mailing list
Crash-utility@xxxxxxxxxx
https://www.redhat.com/mailman/listinfo/crash-utility
