Messages in this thread | | | Subject | Re: Question on "uaccess: Add strict non-pagefault kernel-space read function" | From | Daniel Borkmann <> | Date | Fri, 3 Apr 2020 16:20:24 +0200 |
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Hi Christoph,
On 4/3/20 3:35 PM, Christoph Hellwig wrote: [...] > I just stumbled over your above commit, and it really confuses me. > > Not the newly added functions, which seems perfectly sane, but why you > left the crazy old functions in place instead of investing a little > bit of extra effort to clean the existing mess up and switch everyone > to the sane new variants?
With crazy old functions I presume you mean the old bpf_probe_read() which is mapped to BPF_FUNC_probe_read helper or something else entirely?
For the former, basically my main concern was that these would otherwise break existing tools like bcc/bpftrace/.. unfortunately until they are not converted over yet to _strict variants.
At least on x86, they would still rely on the broken semantic to probe kernel and user memory with probe_read where it 'happens to work', but not on other archs where the address space is not shared.
But once these are fixed, I would love to deprecate these in one way or another. The warning in 00c42373d397 ("x86-64: add warning for non-canonical user access address dereferences") should be a good incentive to switch since people have been hitting it in production as the non-canonical space is sometimes used in user space to tag pointers, for example.
Thanks, Daniel
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