Re: [PATCH v2 0/6] bpf: correct broken uapi for BPF_PROG_TYPE_PERF_EVENT program type

From: Daniel Borkmann
Date: Tue Dec 05 2017 - 10:53:42 EST


On 12/04/2017 10:56 AM, Hendrik Brueckner wrote:
> Perf tool bpf selftests revealed a broken uapi for s390 and arm64.
> With the BPF_PROG_TYPE_PERF_EVENT program type the bpf_perf_event
> structure exports the pt_regs structure for all architectures.
>
> This fails for s390 and arm64 because pt_regs are not part of the
> user api and kept in-kernel only. To mitigate the broken uapi,
> introduce a wrapper that exports pt_regs in an asm-generic way.
> For arm64, export the exising user_pt_regs structure. For s390,
> introduce a user_pt_regs structure that exports the beginning of
> pt_regs.
>
> Note that user_pt_regs must export from the beginning of pt_regs
> as BPF_PROG_TYPE_PERF_EVENT program type is not the only type for
> running BPF programs.
>
> Some more background:
> For the bpf_perf_event, there is a uapi definition that is
> passed to the BPF program. For other "probe" points like
> trace points, kprobes, and uprobes, there is no uapi and the
> BPF program is always passed pt_regs (which is OK as the BPF
> program runs in the kernel context). The perf tool can attach
> BPF programs to all of these "probe" points and, optionally,
> can create a BPF prologue to access particular arguments
> (passed as registers). For this, it uses DWARF/CFI
> information to obtain the register and calls a perf-arch
> backend function, regs_query_register_offset(). This function
> returns the index into (user_)pt_regs for a particular
> register. Then, perf creates a BPF prologue that accesses
> this register based on the passed stucture from the "probe"
> point.
>
> Part of this series, are also updates to the testing and bpf selftest
> to deal with asm-specifics. To complete the bpf support in perf, the
> the regs_query_register_offset function is added for s390 to support
> BPF prologue creation.
>
> Changelog v1 -> v2:
> - Correct kbuild test bot issues by including
> asm-generic/bpf_perf_event.h for archictectures that do not have
> their own asm version.
> - Added patch to clean-up whitespace and coding style issues in s390
> asm/ptrace.h (#4/6) as suggested by Alexei.
>
>
> Hendrik Brueckner (6):
> bpf: correct broken uapi for BPF_PROG_TYPE_PERF_EVENT program type
> s390/bpf: correct broken uapi for BPF_PROG_TYPE_PERF_EVENT program
> type
> arm64/bpf: correct broken uapi for BPF_PROG_TYPE_PERF_EVENT program
> type
> s390/uapi: correct whitespace & coding style in asm/ptrace.h
> selftests/bpf: sync kernel headers and introduce arch support in
> Makefile
> perf s390: add regs_query_register_offset()

Series looks good to me, thanks for working on this Hendrik! If nobody
hollers, I would take the fixes via bpf tree later tonight.

Thanks,
Daniel