On Thu, Aug 29, 2024 at 10:42 AM Andrii Nakryiko <andrii@xxxxxxxxxx> wrote: > > The goal of this patch set is to extend existing ELF build ID parsing logic, > currently mostly used by BPF subsystem, with support for working in sleepable > mode in which memory faults are allowed and can be relied upon to fetch > relevant parts of ELF file to find and fetch .note.gnu.build-id information. > > This is useful and important for BPF subsystem itself, but also for > PROCMAP_QUERY ioctl(), built atop of /proc/<pid>/maps functionality (see [0]), > which makes use of the same build_id_parse() functionality. PROCMAP_QUERY is > always called from sleepable user process context, so it doesn't have to > suffer from current restrictions of build_id_parse() which are due to the NMI > context assumption. > > Along the way, we harden the logic to avoid TOCTOU, overflow, out-of-bounds > access problems. This is the very first patch, which can be backported to > older releases, if necessary. > > We also lift existing limitations of only working as long as ELF program > headers and build ID note section is contained strictly within the very first > page of ELF file. > > We achieve all of the above without duplication of logic between sleepable and > non-sleepable modes through freader abstraction that manages underlying folio > from page cache (on demand) and gives a simple to use direct memory access > interface. With that, single page restrictions and adding sleepable mode > support is rather straightforward. > > We also extend existing set of BPF selftests with a few tests targeting build > ID logic across sleepable and non-sleepabe contexts (we utilize sleepable and > non-sleepable uprobes for that). > > [0] https://lore.kernel.org/linux-mm/20240627170900.1672542-4-andrii@xxxxxxxxxx/ > > v6->v7: > - added filemap_invalidate_{lock,unlock}_shared() around read_cache_folio > and kept Eduard's Reviewed-by (Eduard); > v5->v6: > - use local phnum variable in get_build_id_32() (Jann); > - switch memcmp() instead of strcmp() in parse_build_id() (Jann); > v4->v5: > - pass proper file reference to read_cache_folio() (Shakeel); > - fix another potential overflow due to two u32 additions (Andi); > - add PageUptodate() check to patch #1 (Jann); > v3->v4: > - fix few more potential overflow and out-of-bounds access issues (Andi); > - use purely folio-based implementation for freader (Matthew); Ok, so I'm not sure what one needs to do to get Matthew's attention nowadays, but hopefully yet another ping might do the trick. Matthew, Can you please take another look and provide your ack or nack? I did the conversion to folio as you requested. It would be nice if you can give me a courtesy of acking my patch set, if there is nothing wrong with it, so it can finally go in. Thank you. > v2->v3: > - remove unneeded READ_ONCE()s and force phoff to u64 for 32-bit mode (Andi); > - moved hardening fixes to the front for easier backporting (Jann); > - call freader_cleanup() from build_id_parse_buf() for consistency (Jiri); > v1->v2: > - ensure MADV_PAGEOUT works reliably by paging data in first (Shakeel); > - to fix BPF CI build optionally define MADV_POPULATE_READ in selftest. > > Andrii Nakryiko (10): > lib/buildid: harden build ID parsing logic > lib/buildid: add single folio-based file reader abstraction > lib/buildid: take into account e_phoff when fetching program headers > lib/buildid: remove single-page limit for PHDR search > lib/buildid: rename build_id_parse() into build_id_parse_nofault() > lib/buildid: implement sleepable build_id_parse() API > lib/buildid: don't limit .note.gnu.build-id to the first page in ELF > bpf: decouple stack_map_get_build_id_offset() from > perf_callchain_entry > bpf: wire up sleepable bpf_get_stack() and bpf_get_task_stack() > helpers > selftests/bpf: add build ID tests > > include/linux/bpf.h | 2 + > include/linux/buildid.h | 4 +- > kernel/bpf/stackmap.c | 131 ++++-- > kernel/events/core.c | 2 +- > kernel/trace/bpf_trace.c | 5 +- > lib/buildid.c | 397 +++++++++++++----- > tools/testing/selftests/bpf/Makefile | 5 +- > .../selftests/bpf/prog_tests/build_id.c | 118 ++++++ > .../selftests/bpf/progs/test_build_id.c | 31 ++ > tools/testing/selftests/bpf/uprobe_multi.c | 41 ++ > tools/testing/selftests/bpf/uprobe_multi.ld | 11 + > 11 files changed, 605 insertions(+), 142 deletions(-) > create mode 100644 tools/testing/selftests/bpf/prog_tests/build_id.c > create mode 100644 tools/testing/selftests/bpf/progs/test_build_id.c > create mode 100644 tools/testing/selftests/bpf/uprobe_multi.ld > > -- > 2.43.5 >
