On Fri, 22 Feb 2019 17:27:45 +0900 Masami Hiramatsu mhiramat@kernel.org wrote:
Hi Steve,
On Wed, 20 Feb 2019 09:49:26 -0500 Steven Rostedt rostedt@goodmis.org wrote:
On Wed, 20 Feb 2019 17:10:19 +0900 Masami Hiramatsu mhiramat@kernel.org wrote:
Let me ensure what you want. So you want to access a "string" in user-space, not a data structure? In that case, it is very easy to me. It is enough to add a "ustring" type to kprobe events. For example, do_sys_opsn's path variable is one example. That will be +0(+0(%si)):ustring, and fetcher finally copy the string using strncpy_from_user() instead of strncpy_from_unsafe(). (*)
ustring would be good.
I've tried to implement ustring and u-offsets, but I got some issues.
- access_ok() warns if it is called in IRQ context (kprobes is.)
- copy_from_user uses access_ok(), so it is not designed for irq handler.
Moreover, if we have different kernel/user address spaces, we have to assign target user-pages to kernel vma. Can we do that (doesn't it involve mutex locks)?
Or, can we do this?
long __probe_user_read(void *dst, const void *src, size_t size) { long ret; mm_segment_t old_fs = get_fs();
set_fs(USER_DS); /* Only this is changed */ pagefault_disable(); current->kernel_uaccess_faults_ok++; ret = __copy_from_user_inatomic(dst, (__force const void __user *)src, size); current->kernel_uaccess_faults_ok--; pagefault_enable(); set_fs(old_fs);
return ret ? -EFAULT : 0; }