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Thu, 04 Dec 2025 06:04:25 -0800 (PST) From: Jiri Olsa X-Google-Original-From: Jiri Olsa Date: Thu, 4 Dec 2025 15:04:23 +0100 To: Josh Poimboeuf Cc: x86@kernel.org, linux-kernel@vger.kernel.org, live-patching@vger.kernel.org, bpf@vger.kernel.org, Andrey Grodzovsky , Petr Mladek , Song Liu , Raja Khan , Miroslav Benes , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Peter Zijlstra Subject: Re: [PATCH v2 1/2] bpf: Add bpf_has_frame_pointer() Message-ID: References: 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: On Wed, Dec 03, 2025 at 07:32:15PM -0800, Josh Poimboeuf wrote: > Introduce a bpf_has_frame_pointer() helper that unwinders can call to > determine whether a given instruction pointer is within the valid frame > pointer region of a BPF JIT program or trampoline (i.e., after the > prologue, before the epilogue). > > This will enable livepatch (with the ORC unwinder) to reliably unwind > through BPF JIT frames. > > Acked-by: Song Liu > Acked-and-tested-by: Andrey Grodzovsky > Signed-off-by: Josh Poimboeuf > --- > arch/x86/net/bpf_jit_comp.c | 12 ++++++++++++ > include/linux/bpf.h | 3 +++ > kernel/bpf/core.c | 16 ++++++++++++++++ > 3 files changed, 31 insertions(+) > > diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c > index de5083cb1d37..3ec4fa94086a 100644 > --- a/arch/x86/net/bpf_jit_comp.c > +++ b/arch/x86/net/bpf_jit_comp.c > @@ -1661,6 +1661,9 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image, u8 *rw_image > emit_prologue(&prog, image, stack_depth, > bpf_prog_was_classic(bpf_prog), tail_call_reachable, > bpf_is_subprog(bpf_prog), bpf_prog->aux->exception_cb); > + > + bpf_prog->aux->ksym.fp_start = prog - temp; > + > /* Exception callback will clobber callee regs for its own use, and > * restore the original callee regs from main prog's stack frame. > */ > @@ -2716,6 +2719,8 @@ st: if (is_imm8(insn->off)) > pop_r12(&prog); > } > EMIT1(0xC9); /* leave */ > + bpf_prog->aux->ksym.fp_end = prog - temp; > + > emit_return(&prog, image + addrs[i - 1] + (prog - temp)); > break; > > @@ -3299,6 +3304,9 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *rw_im > } > EMIT1(0x55); /* push rbp */ > EMIT3(0x48, 0x89, 0xE5); /* mov rbp, rsp */ > + if (im) > + im->ksym.fp_start = prog - (u8 *)rw_image; > + > if (!is_imm8(stack_size)) { > /* sub rsp, stack_size */ > EMIT3_off32(0x48, 0x81, 0xEC, stack_size); > @@ -3436,7 +3444,11 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *rw_im > emit_ldx(&prog, BPF_DW, BPF_REG_0, BPF_REG_FP, -8); > > emit_ldx(&prog, BPF_DW, BPF_REG_6, BPF_REG_FP, -rbx_off); > + > EMIT1(0xC9); /* leave */ > + if (im) > + im->ksym.fp_end = prog - (u8 *)rw_image; is the null check needed? there are other places in the function that use 'im' without that thanks, jirka > + > if (flags & BPF_TRAMP_F_SKIP_FRAME) { > /* skip our return address and return to parent */ > EMIT4(0x48, 0x83, 0xC4, 8); /* add rsp, 8 */ > diff --git a/include/linux/bpf.h b/include/linux/bpf.h > index d808253f2e94..e3f56e8443da 100644 > --- a/include/linux/bpf.h > +++ b/include/linux/bpf.h > @@ -1257,6 +1257,8 @@ struct bpf_ksym { > struct list_head lnode; > struct latch_tree_node tnode; > bool prog; > + u32 fp_start; > + u32 fp_end; > }; > > enum bpf_tramp_prog_type { > @@ -1483,6 +1485,7 @@ void bpf_image_ksym_add(struct bpf_ksym *ksym); > void bpf_image_ksym_del(struct bpf_ksym *ksym); > void bpf_ksym_add(struct bpf_ksym *ksym); > void bpf_ksym_del(struct bpf_ksym *ksym); > +bool bpf_has_frame_pointer(unsigned long ip); > int bpf_jit_charge_modmem(u32 size); > void bpf_jit_uncharge_modmem(u32 size); > bool bpf_prog_has_trampoline(const struct bpf_prog *prog); > diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c > index d595fe512498..7cd8382d1152 100644 > --- a/kernel/bpf/core.c > +++ b/kernel/bpf/core.c > @@ -760,6 +760,22 @@ struct bpf_prog *bpf_prog_ksym_find(unsigned long addr) > NULL; > } > > +bool bpf_has_frame_pointer(unsigned long ip) > +{ > + struct bpf_ksym *ksym; > + unsigned long offset; > + > + guard(rcu)(); > + > + ksym = bpf_ksym_find(ip); > + if (!ksym || !ksym->fp_start || !ksym->fp_end) > + return false; > + > + offset = ip - ksym->start; > + > + return offset >= ksym->fp_start && offset < ksym->fp_end; > +} > + > const struct exception_table_entry *search_bpf_extables(unsigned long addr) > { > const struct exception_table_entry *e = NULL; > -- > 2.51.1 > >