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[37.188.200.155]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-b7359bfb238sm13421466b.14.2025.11.12.23.51.03 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 12 Nov 2025 23:51:05 -0800 (PST) From: Jiri Olsa X-Google-Original-From: Jiri Olsa Date: Thu, 13 Nov 2025 08:51:00 +0100 To: Masami Hiramatsu , Steven Rostedt , Will Deacon Cc: Peter Zijlstra , bpf@vger.kernel.org, linux-trace-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, x86@kernel.org, Yonghong Song , Song Liu , Andrii Nakryiko , Mark Rutland , Mahe Tardy Subject: Re: [BUG/RFC 1/2] arm64/ftrace,bpf: Fix partial regs after bpf_prog_run Message-ID: References: <20251105125924.365205-1-jolsa@kernel.org> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251105125924.365205-1-jolsa@kernel.org> ping, thanks jirka On Wed, Nov 05, 2025 at 01:59:23PM +0100, Jiri Olsa wrote: > hi, > Mahe reported issue with bpf_override_return helper not working > when executed from kprobe.multi bpf program on arm. > > The problem seems to be that on arm we use alternate storage for > pt_regs object that is passed to bpf_prog_run and if any register > is changed (which is the case of bpf_override_return) it's not > propagated back to actual pt_regs object. > > The change below seems to fix the issue, but I have no idea if > that's proper fix for arm, thoughts? > > I'm attaching selftest to actually test bpf_override_return helper > functionality, because currently we only test that we are able to > attach a program with it, but not the override itself. > > thanks, > jirka > > > --- > arch/arm64/include/asm/ftrace.h | 11 +++++++++++ > include/linux/ftrace.h | 3 +++ > kernel/trace/bpf_trace.c | 1 + > 3 files changed, 15 insertions(+) > > diff --git a/arch/arm64/include/asm/ftrace.h b/arch/arm64/include/asm/ftrace.h > index ba7cf7fec5e9..ad6cf587885c 100644 > --- a/arch/arm64/include/asm/ftrace.h > +++ b/arch/arm64/include/asm/ftrace.h > @@ -157,6 +157,17 @@ ftrace_partial_regs(const struct ftrace_regs *fregs, struct pt_regs *regs) > return regs; > } > > +static __always_inline void > +ftrace_partial_regs_fix(const struct ftrace_regs *fregs, struct pt_regs *regs) > +{ > + struct __arch_ftrace_regs *afregs = arch_ftrace_regs(fregs); > + > + if (afregs->pc != regs->pc) { > + afregs->pc = regs->pc; > + afregs->regs[0] = regs->regs[0]; > + } > +} > + > #define arch_ftrace_fill_perf_regs(fregs, _regs) do { \ > (_regs)->pc = arch_ftrace_regs(fregs)->pc; \ > (_regs)->regs[29] = arch_ftrace_regs(fregs)->fp; \ > diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h > index 7ded7df6e9b5..4cb1315522bb 100644 > --- a/include/linux/ftrace.h > +++ b/include/linux/ftrace.h > @@ -205,6 +205,9 @@ ftrace_partial_regs(struct ftrace_regs *fregs, struct pt_regs *regs) > return &arch_ftrace_regs(fregs)->regs; > } > > +static __always_inline void > +ftrace_partial_regs_fix(struct ftrace_regs *fregs, struct pt_regs *regs) { } > + > #endif /* !CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS || CONFIG_HAVE_FTRACE_REGS_HAVING_PT_REGS */ > > #ifdef CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS > diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c > index a795f7afbf3d..7b5768ced9b3 100644 > --- a/kernel/trace/bpf_trace.c > +++ b/kernel/trace/bpf_trace.c > @@ -2564,6 +2564,7 @@ kprobe_multi_link_prog_run(struct bpf_kprobe_multi_link *link, > old_run_ctx = bpf_set_run_ctx(&run_ctx.session_ctx.run_ctx); > err = bpf_prog_run(link->link.prog, regs); > bpf_reset_run_ctx(old_run_ctx); > + ftrace_partial_regs_fix(fregs, bpf_kprobe_multi_pt_regs_ptr()); > rcu_read_unlock(); > > out: > -- > 2.51.1 >