From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from 66-220-144-178.mail-mxout.facebook.com (66-220-144-178.mail-mxout.facebook.com [66.220.144.178]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 82AF81A704B for ; Thu, 15 Oct 2026 04:03:13 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=66.220.144.178 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1792036994; cv=none; b=S5IA6GstjxlxWvtfop6nzmKHk4GnnoAh9KSN3lNCOJAGj8eXY8ejnpFxbgKKP4WZr8g4Oo/Q0kWe+oVhc7ZOdyEjO8HK0pGsaV4sBrm6Yi8A7okDsBTJKnH6rUYY0r57Ot/8STIxGWu+I4nJR5o18v2O/HI/KslAajn7LoC6Xos= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1792036994; c=relaxed/simple; bh=raNbR0mXfww8vQQXDL/O4k0kcVV3dcCFHuzPUjs9BwE=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=c+vCde3HmKKS4Rf1DVl4o+rf1X6JUcufGe5/bKnnqWj9OR9ZH26hpMI/iknE093CEl/tXVVqnnX5Uk3ReH8gzeC3li5Sy0jRlhCkveMxZ5sOp971xxmk7bwK5wMYJdTRdEpuVnLoPanpsHrauL5eg7otiFrPnzn9CqrCJIaNnvQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.dev; spf=fail smtp.mailfrom=linux.dev; arc=none smtp.client-ip=66.220.144.178 Authentication-Results: smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=fail smtp.mailfrom=linux.dev Received: by devvm16039.vll0.facebook.com (Postfix, from userid 128203) id C45B73149957F4; Wed, 14 Oct 2026 21:03:10 -0700 (PDT) From: Yonghong Song To: bpf@vger.kernel.org Cc: Alexei Starovoitov , Andrii Nakryiko , Daniel Borkmann , Eduard Zingerman , kernel-team@fb.com Subject: [PATCH bpf-next v11 17/26] bpf, arm64: Dispatch exception cleanup pads at run time Date: Wed, 14 Oct 2026 21:03:10 -0700 Message-ID: <20261015040310.864133-1-yonghong.song@linux.dev> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20261015040143.854070-1-yonghong.song@linux.dev> References: <20261015040143.854070-1-yonghong.song@linux.dev> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Add what bpf_unwind() relies on to send each frame of a program to its landing pad or its epilogue on arm64, as the previous patch does for x86-64: - arch_bpf_stack_walk_ra(): walks the frame records with the kernel unwinder, handing each return address to the consumer and storing a new one back into the record it was read from. The first frame, whose return into bpf_unwind() comes from the walk's own record, is skipped. - With CONFIG_ARM64_PTR_AUTH_KERNEL and a CPU that supports address authentication, the new address is signed the way the BPF prologue's PACIASP signs the link register, key IA with the record + 16 as modifier, using PACIA1716 so that no assembler support for pointer authentication is needed. - Once the image is final, the JIT fills in the native cleanup table and records each function's epilogue address in aux->epilogue_ip, where an unwind sends a frame with no pad. - bpf_jit_supports_cleanup_pads() says yes, also with a shadow call stack: only JITed frames' records are written, and JITed code keeps no x18 copy of its return address. A pad needs no BTI: it is only reached as a return address. Signed-off-by: Yonghong Song --- arch/arm64/kernel/stacktrace.c | 77 ++++++++++++++++++++++++++++++++++ arch/arm64/net/bpf_jit_comp.c | 16 +++++++ 2 files changed, 93 insertions(+) diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrac= e.c index 3ebcf8c53fb0..6ff485280da5 100644 --- a/arch/arm64/kernel/stacktrace.c +++ b/arch/arm64/kernel/stacktrace.c @@ -445,6 +445,83 @@ noinline noinstr void arch_bpf_stack_walk(bool (*con= sume_entry)(void *cookie, u6 kunwind_stack_walk(arch_bpf_unwind_consume_entry, &data, current, NULL)= ; } =20 +struct bpf_unwind_ra_consume_entry_data { + bool (*consume_entry)(void *cookie, u64 ip, u64 sp, u64 fp, u64 *ra); + void *cookie; + unsigned long record; + bool seen_first; +}; + +/* PACIA1716 (hint #8): sign x17 with the modifier in x16, under key IA.= */ +static u64 bpf_unwind_sign_ra(u64 ra, u64 modifier) +{ + register u64 x17 asm("x17") =3D ra; + register u64 x16 asm("x16") =3D modifier; + + asm volatile(ARM64_ASM_PREAMBLE + " hint #8\n" + : "+r" (x17) : "r" (x16)); + return x17; +} + +/* PACIASP's modifier is the entry sp, record + 16 for a BPF prologue. *= / +static void bpf_unwind_store_ra(unsigned long record, u64 ra) +{ + struct frame_record *rec =3D (struct frame_record *)record; + + /* + * Whether the slot holds a signed address is a property of the build, + * not one to be read off the value: a PAC can come out equal to the + * bits stripping puts back, and a signed address would then be taken + * for an unsigned one. What signs is CONFIG_ARM64_PTR_AUTH_KERNEL -- + * the prologue here, and -mbranch-protection for everything the + * compiler emits. + */ + if (IS_ENABLED(CONFIG_ARM64_PTR_AUTH_KERNEL) && + system_supports_address_auth()) + ra =3D bpf_unwind_sign_ra(ra, record + sizeof(struct frame_record)); + WRITE_ONCE(rec->lr, ra); +} + +static bool +arch_bpf_unwind_ra_consume_entry(const struct kunwind_state *state, void= *cookie) +{ + struct bpf_unwind_ra_consume_entry_data *data =3D cookie; + unsigned long record =3D data->record; + bool seen_first =3D data->seen_first; + u64 ra =3D state->common.pc; + bool cont; + + /* The record this frame's return address will have come out of. */ + data->record =3D state->common.fp; + data->seen_first =3D true; + + /* + * The first pc returns into bpf_unwind(), from this walk's own frame + * record: not a BPF frame, and not one to redirect. + */ + if (!seen_first) + return true; + /* A consumer that stops still gets to redirect the frame it stopped on= . */ + cont =3D data->consume_entry(data->cookie, state->common.pc, 0, + state->common.fp, &ra); + if (ra !=3D state->common.pc) + bpf_unwind_store_ra(record, ra); + return cont; +} + +noinline noinstr void arch_bpf_stack_walk_ra(bool (*consume_entry)(void = *cookie, u64 ip, u64 sp, + u64 fp, u64 *ra), + void *cookie) +{ + struct bpf_unwind_ra_consume_entry_data data =3D { + .consume_entry =3D consume_entry, + .cookie =3D cookie, + }; + + kunwind_stack_walk(arch_bpf_unwind_ra_consume_entry, &data, current, NU= LL); +} + static const char *state_source_string(const struct kunwind_state *state= ) { switch (state->source) { diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.= c index 506c4201fec8..c8c0328b3219 100644 --- a/arch/arm64/net/bpf_jit_comp.c +++ b/arch/arm64/net/bpf_jit_comp.c @@ -2422,6 +2422,17 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_ve= rifier_env *env, struct bpf_pr * reasons, expects to point to the next instruction) */ bpf_prog_update_insn_ptrs(prog, ctx.offset, ctx.ro_image); + + /* + * Same byte offsets, consumed by the bpf_unwind() walk: + * turn the cleanup records into native address ranges now that + * the image is final. + */ + bpf_exc_fill_native_ranges(prog, ctx.offset, ctx.ro_image); + + /* Where an unwind sends a frame with no pad. */ + prog->aux->epilogue_ip =3D (u64)ctx.ro_image + + ctx.epilogue_offset * AARCH64_INSN_SIZE; out_off: if (!ro_header && priv_stack_ptr) { free_percpu(priv_stack_ptr); @@ -3415,6 +3426,11 @@ bool bpf_jit_supports_exceptions(void) return true; } =20 +bool bpf_jit_supports_cleanup_pads(void) +{ + return true; +} + bool bpf_jit_supports_arena(void) { return true; --=20 2.53.0-Meta