linux-kernel - Re: [PATCH v2 0/6] bpf: correct broken uapi for BPF_PROG_TYPE_PERF

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Message-ID: <e879ca95-25d7-d7b6-e811-81a5017ea5cf@iogearbox.net>
Date:   Tue, 5 Dec 2017 16:53:20 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Hendrik Brueckner <brueckner@...ux.vnet.ibm.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Will Deacon <will.deacon@....com>,
        Ingo Molnar <mingo@...hat.com>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Peter Zijlstra <peterz@...radead.org>,
        "David S. Miller" <davem@...emloft.net>,
        linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
        netdev@...r.kernel.org
Subject: Re: [PATCH v2 0/6] bpf: correct broken uapi for
 BPF_PROG_TYPE_PERF_EVENT program type

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