instrument_copy_to_user(9)

💅 instrument_copy_to_user(9) 💅

okay so this is a page from the Kernel API Manual, and bestie, we're about to get into it — it's giving "low-level kernel instrumentation" and honestly? iconic.

✨ NAME ✨

instrument_copy_to_user — literally the thing that instruments the reads that happen because of copy_to_user 🫶

🌸 SYNOPSIS 🌸

void instrument_copy_to_user (void __user *to , const void *from ,
       unsigned long n );

🎀 ARGUMENTS 🎀

• to — the destination address, like where the stuff is headed 💖
• from — the source address, aka where it's coming from 🦋
• n — the number of bytes to copy, yes we're counting 📏

💅 DESCRIPTION 💅

So what this does is it instruments reads from kernel memory — and those reads are happening because of copy_to_user (and its variants, you know the fam 👑).

⚠️ important vibe check: the instrumentation has to be inserted before the accesses. Not after. Before. no cap, this is not a drill 😭

🔥 SEE ALSO 🔥

Kernel file ./include/linux/instrumented.h — and like, the whole friend group:

• instrument_read(9)
• instrument_write(9)
• instrument_read_write(9)
• instrument_atomic_read(9)
• instrument_atomic_write(9)
• instrument_atomic_read_write(9)
• instrument_copy_from_user_before(9)
• instrument_copy_from_user_after(9)
• instrument_memcpy_before(9)
• instrument_memcpy_after(9)
• instrument_get_user(9)
• instrument_put_user(9)

mwah 💋 that's the whole page — brought to you from ./include/linux, dated October 2026, in the Kernel API Manual. slay, go instrument responsibly ✨💜