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

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(a)suse.com&gt; --- 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

+ +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(a)redhat.com https://www.redhat.com/mailman/listinfo/crash-utility