kmsan_copy_to_user(9)

💅 NAME 💅

okay so bestie, meet kmsan_copy_to_user(9) from the Kernel API Manual — it’s literally the function that notifies KMSAN about a data transfer to userspace. no cap, that’s the whole name-and-purpose moment ✨

✨ SYNOPSIS ✨

void kmsan_copy_to_user (void __user *to , const void *from , size_t
       to_copy , size_t left );

🎀 ARGUMENTS 🎀

• to — the destination address in the userspace 💖 where the data is headed.
• from — the source address in the kernel 🌸 where the data is coming from.
• to_copy — the number of bytes to copy 🎀
• left — the number of bytes not copied 👀

🔥 DESCRIPTION 🔥

So here’s the tea: if this is a real userspace data transfer, KMSAN does a little vibe check on the bytes that were actually copied to make sure there was no information leak 🔍✨

And if to belongs to the kernel space — which is possible for compat syscalls — KMSAN just copies the metadata. periodt 💅

🌈 SEE ALSO 🌈

• Kernel file ./include/linux/kmsan-checks.h
• kmsan_poison_memory(9)
• kmsan_unpoison_memory(9)
• kmsan_check_memory(9)
• kmsan_memmove(9)

okay that’s the whole page, bestie 🫶 source/version ./include/linux, dated October 2026, page kmsan_copy_to_user(9) — mwah 💋