Messages in this thread | | | Date | Mon, 19 Jun 2023 11:17:08 -0700 | Subject | Re: [PATCH bpf] bpf/btf: Accept function names that contain dots | From | Yonghong Song <> |
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On 6/19/23 7:03 AM, Florent Revest wrote: > On Fri, Jun 16, 2023 at 6:57 PM Andrii Nakryiko > <andrii.nakryiko@gmail.com> wrote: >> >> On Thu, Jun 15, 2023 at 7:56 AM Florent Revest <revest@chromium.org> wrote: >>> >>> When building a kernel with LLVM=1, LLVM_IAS=0 and CONFIG_KASAN=y, LLVM >>> leaves DWARF tags for the "asan.module_ctor" & co symbols. In turn, >>> pahole creates BTF_KIND_FUNC entries for these and this makes the BTF >>> metadata validation fail because they contain a dot. >>> >>> In a dramatic turn of event, this BTF verification failure can cause >>> the netfilter_bpf initialization to fail, causing netfilter_core to >>> free the netfilter_helper hashmap and netfilter_ftp to trigger a >>> use-after-free. The risk of u-a-f in netfilter will be addressed >>> separately but the existence of "asan.module_ctor" debug info under some >>> build conditions sounds like a good enough reason to accept functions >>> that contain dots in BTF. >> >> I don't see much harm in allowing dots. There are also all those .isra >> and other modifications to functions that we currently don't have in >> BTF, but with the discussions about recording function addrs we might >> eventually have those as well. So: >> >> Acked-by: Andrii Nakryiko <andrii@kernel.org> > > Thanks Andrii! :) > >>> Cc: stable@vger.kernel.org >>> Fixes: 1dc92851849c ("bpf: kernel side support for BTF Var and DataSec") > > So do you think these trailers should be kept ? I suppose we can > either see this as a "new feature" to accommodate .isra that should go > through bpf-next or as a bug fix that goes through bpf and gets > backported to stable (without this, BTF wouldn't work on old kernels > built under a new clang and with LLVM_IAS=0 and CONFIG_KASAN=y so this > sounds like a legitimate bug fix to me, I just wanted to double check)
How many people really build the kernel with LLVM=1 LLVM_IAS=0 which uses clang compiler ans gcc 'as'. I think distro most likely won't do this if they intend to build the kernel with clang.
Note that LLVM=1 implies to use both clang compiler and clang assembler.
Using clang17 and 'LLVM=1 LLVM_IAS=0', with latest bpf-next, I actually hit some build errors like:
/tmp/video-bios-59fa52.s: Assembler messages: /tmp/video-bios-59fa52.s:4: Error: junk at end of line, first unrecognized character is `"' /tmp/video-bios-59fa52.s:4: Error: file number less than one /tmp/video-bios-59fa52.s:5: Error: junk at end of line, first unrecognized character is `"' /tmp/video-bios-59fa52.s:6: Error: junk at end of line, first unrecognized character is `"' /tmp/video-bios-59fa52.s:7: Error: junk at end of line, first unrecognized character is `"' /tmp/video-bios-59fa52.s:8: Error: junk at end of line, first unrecognized character is `"' /tmp/video-bios-59fa52.s:9: Error: junk at end of line, first unrecognized character is `"' /tmp/video-bios-59fa52.s:10: Error: junk at end of line, first unrecognized character is `"' /tmp/video-bios-59fa52.s:68: Error: junk at end of line, first unrecognized character is `"' clang: error: assembler command failed with exit code 1 (use -v to see invocation) make[4]: *** [/home/yhs/work/bpf-next/scripts/Makefile.build:252: arch/x86/realmode/rm/video-bios.o] Error 1 make[4]: *** Waiting for unfinished jobs.... /tmp/wakemain-88777c.s: Assembler messages: /tmp/wakemain-88777c.s:4: Error: junk at end of line, first unrecognized character is `"' /tmp/wakemain-88777c.s:4: Error: file number less than one /tmp/wakemain-88777c.s:5: Error: junk at end of line, first unrecognized character is `"' /tmp/wakemain-88777c.s:6: Error: junk at end of line, first unrecognized character is `"' /tmp/wakemain-88777c.s:7: Error: junk at end of line, first unrecognized character is `"' /tmp/wakemain-88777c.s:8: Error: junk at end of line, first unrecognized character is `"' /tmp/wakemain-88777c.s:81: Error: junk at end of line, first unrecognized character is `"' /tmp/wakemain-88777c.s:312: Error: junk at end of line, first unrecognized character is `"' clang: error: assembler command failed with exit code 1 (use -v to see invocation)
Potentially because of my local gnu assembler 2.30-120.el8 won't work with some syntax generated by clang. Mixing clang compiler and arbitrary gnu assembler are not a good idea (see the above example). It might work with close-to-latest gnu assembler.
To support function name like '<fname>.isra', some llvm work will be needed, and it may take some time.
So in my opinion, this patch is NOT a bug fix. It won't affect distro. Whether we should backport to the old kernel, I am not sure whether it is absolutely necessary as casual build can always remove LLVM_IAS=0 or hack the kernel source itself.
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