On Fri, Dec 13, 2024 at 11:51:05AM +0100, Peter Zijlstra wrote: > On Wed, Dec 11, 2024 at 02:33:49PM +0100, Jiri Olsa wrote: > > hi, > > this patchset adds support to optimize usdt probes on top of 5-byte > > nop instruction. > > > > The generic approach (optimize all uprobes) is hard due to emulating > > possible multiple original instructions and its related issues. The > > usdt case, which stores 5-byte nop seems much easier, so starting > > with that. > > > > The basic idea is to replace breakpoint exception with syscall which > > is faster on x86_64. For more details please see changelog of patch 8. > > So ideally we'd put a check in the syscall, which verifies it comes from > one of our trampolines and reject any and all other usage. > > The reason to do this is that we can then delete all this code the > moment it becomes irrelevant without having to worry userspace might be > 'creative' somewhere. yes, we do that already in SYSCALL_DEFINE0(uprobe): /* Allow execution only from uprobe trampolines. */ vma = vma_lookup(current->mm, regs->ip); if (!vma || vma->vm_private_data != (void *) &tramp_mapping) { force_sig(SIGILL); return -1; } jirka