> > uprobe_mmap()->install_breakpoint() can fail if the probed insn is not > > supported > > But there are other reasons why it can fail, > > > However failing mmap_region()/do_fork() because of a probe on an > > unsupported instruction is wrong. > > Srikar, I strongly, absolutely disagree. Please correct me, but.. > > Do you realize how much uprobes hooks in mmap_region/dup_mmap are broken? > > (cough, can't resist, vma_adjust()->uprobe_mmap() is not right too, but > this is another story). > > OK, lets start with dup_mmap: > > // retval == 0 > > if (file && uprobe_mmap(tmp)) > goto out; > > out: > up_write(&mm->mmap_sem); > flush_tlb_mm(oldmm); > up_write(&oldmm->mmap_sem); > return retval; > > Given that retval == 0, what do you think dup_mmap() returns if > uprobe_mmap() fails? And note that we didn't copy all vmas. > OK, at least this can't crash (afaics), and easy to fix. > > > But mmap_region() is worse, much worse. It simply can _not_ fail > after uprobe_mmap (of course, I am not saying this is unfixable) > without the crash. And note that the crash is "delayed". And btw, > like dup_mmap(), mmap_region() doesn't return the error too.
Oh, thats really a bad mistake from my side. I apologize. > > Srikar, I strongly believe this horror must not exist. Either > we should teach mmap_region() and dup_mmap() (and vma_adjust!) > to fail correctly, or we should ignore the error code. > > It is that simple, isn't it? > Right. > Whatever you do with uprobe_mmap(), even if you change it to always > return 0, the code in mmap_region() is absolutely, absolutely broken. > But uprobe_mmap() still needs to walk thro the probe list and insert the other probes. Currently we just ignore the remaining probes and that has to be fixed within uprobe_mmap. > Do you agree? > > And once again. I agree, in the long term we should reconsider > this change. But we need a simple fix for now/stable. > Agree. > > Hence change uprobe_mmap() to ignore unsupported instructions. > > OK. Now suppose that mmap_region()-> uprobe_mmap() fails because > the caller is SIGKILL'ed (so __get_user_pages fails). Given that > mmap_region() can't handle the error correctly, the kernel can > crash. > How about having your fix + my patch to fix the uprobe_mmap()? -- Thanks and Regards Srikar -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
