From: Eduard Zingerman <eddyz87@gmail.com>
To: Alexei Starovoitov <alexei.starovoitov@gmail.com>, bpf@vger.kernel.org
Cc: daniel@iogearbox.net, andrii@kernel.org, memxor@gmail.com,
a.s.protopopov@gmail.com
Subject: Re: [PATCH bpf-next 05/17] bpf: Add callx instruction to call bpf subprogs indirectly
Date: Wed, 23 Sep 2026 17:09:56 -0700 [thread overview]
Message-ID: <0e1bdfe95f011b5074fe9eb5306f9a5255293188.camel@gmail.com> (raw)
In-Reply-To: <20260922011323.1298619-6-alexei.starovoitov@gmail.com>
On Tue, 2026-09-22 at 01:13 +0000, Alexei Starovoitov wrote:
> From: Alexei Starovoitov <ast@kernel.org>
>
> Introduce BPF_JMP | BPF_CALL | BPF_X (opcode 0x8d) 'callx dst_reg'
> instruction: indirect call of bpf subprog with address in dst_reg.
> That's the encoding LLVM emits for calls via function pointer.
> src_reg, off, imm are reserved and must be zero.
>
> dst_reg must be PTR_TO_FUNC produced by ld_imm64 BPF_PSEUDO_FUNC.
> check_ld_imm() allows it for static subprogs only, so callx cannot call
> global subprogs or the main prog. Since every callee has its address
> taken by ld_imm64, add_subprogs() and check_cfg() see all of them before
> the main pass, and might_sleep, changes_pkt_data, might_throw of
> the callee are already merged into the subprog that takes the address.
>
> reg->subprogno is the callee. Verify callx as a direct call of that
> static subprog: split check_func_call() into check_static_func_call()
> that is shared with new check_func_callx(). Different paths through
> the same callx may call different subprogs.
>
> Arithmetic on PTR_TO_FUNC is allowed, so check that the pointer wasn't
> modified. Allow callx while holding a lock like direct calls of static
> subprogs.
>
> The interpreter doesn't support callx. Set jit_required and add
> bpf_jit_supports_callx() for JITs to opt in. No JIT does yet, so callx
> is still rejected.
>
> Print it as "callx rN" in the verifier log and xlated dump.
>
> Adjust "invalid call insn1" test_verifier test that used opcode 0x8d as
> unknown opcode. It fails with "R0 !read_ok" now.
>
> Signed-off-by: Alexei Starovoitov <ast@kernel.org>
> ---
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
...
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 72ea662baea5..0d32d3921210 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
...
> @@ -18725,7 +18806,8 @@ static int do_check_insn(struct bpf_verifier_env *env, bool *do_print_state)
>
> env->jmps_processed++;
> if (opcode == BPF_CALL) {
> - if (env->cur_state->active_locks) {
> + /* similar to static subprog calls callx is allowed under a lock */
> + if (env->cur_state->active_locks && !bpf_is_callx(insn)) {
Nit: moving !bpf_is_callx(insn) inside the nested 'if' would have been less surprising.
> if ((insn->src_reg == BPF_REG_0 &&
> insn->imm != BPF_FUNC_spin_unlock &&
> insn->imm != BPF_FUNC_kptr_xchg) ||
...
next prev parent reply other threads:[~2026-09-24 0:09 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-22 1:13 [PATCH bpf-next 00/17] bpf: Indirect calls of bpf subprogs (callx) Alexei Starovoitov
2026-09-22 1:13 ` [PATCH bpf-next 01/17] bpf: Fix infinite loop in check_max_stack_depth() Alexei Starovoitov
2026-09-22 2:01 ` bot+bpf-ci
2026-09-22 2:56 ` Alexei Starovoitov
2026-09-23 22:35 ` Eduard Zingerman
2026-09-22 1:13 ` [PATCH bpf-next 02/17] selftests/bpf: Test recursion through a global function and a callback Alexei Starovoitov
2026-09-22 1:13 ` [PATCH bpf-next 03/17] bpf: Don't fold loads from insn_array maps into constants Alexei Starovoitov
2026-09-23 22:39 ` Eduard Zingerman
2026-09-23 23:12 ` Alexei Starovoitov
2026-09-24 0:19 ` bot+bpf-ci
2026-09-22 1:13 ` [PATCH bpf-next 04/17] bpf: Prepare static analysis passes for callx instruction Alexei Starovoitov
2026-09-23 23:10 ` Eduard Zingerman
2026-09-23 23:51 ` Alexei Starovoitov
2026-09-22 1:13 ` [PATCH bpf-next 05/17] bpf: Add callx instruction to call bpf subprogs indirectly Alexei Starovoitov
2026-09-24 0:09 ` Eduard Zingerman [this message]
2026-09-22 1:13 ` [PATCH bpf-next 06/17] bpf: Add callx calls to the call graph Alexei Starovoitov
2026-09-22 1:27 ` sashiko-bot
2026-09-22 2:54 ` Alexei Starovoitov
2026-09-22 1:13 ` [PATCH bpf-next 07/17] bpf, x86: Add JIT support for callx Alexei Starovoitov
2026-09-22 1:27 ` sashiko-bot
2026-09-22 2:53 ` Alexei Starovoitov
2026-09-22 1:13 ` [PATCH bpf-next 08/17] bpf, arm64: " Alexei Starovoitov
2026-09-22 15:05 ` Puranjay Mohan
2026-09-22 1:13 ` [PATCH bpf-next 09/17] bpf: Discover subprogs described by func_info Alexei Starovoitov
2026-09-22 1:13 ` [PATCH bpf-next 10/17] bpf: Recognize pointers to functions in read-only maps Alexei Starovoitov
2026-09-22 1:31 ` sashiko-bot
2026-09-22 3:01 ` Alexei Starovoitov
2026-09-24 0:46 ` bot+bpf-ci
2026-09-24 2:12 ` Alexei Starovoitov
2026-09-22 1:13 ` [PATCH bpf-next 11/17] libbpf: Support pointers to static functions in data when linking Alexei Starovoitov
2026-09-22 1:13 ` [PATCH bpf-next 12/17] libbpf: Resolve pointers to functions in read-only data Alexei Starovoitov
2026-09-24 0:33 ` bot+bpf-ci
2026-09-24 2:13 ` Alexei Starovoitov
2026-09-22 1:13 ` [PATCH bpf-next 13/17] libbpf: Treat .data.rel.ro as " Alexei Starovoitov
2026-09-22 1:13 ` [PATCH bpf-next 14/17] libbpf: Support pointers to functions in read-only data in light skeleton Alexei Starovoitov
2026-09-22 2:01 ` bot+bpf-ci
2026-09-22 2:55 ` Alexei Starovoitov
2026-09-22 1:13 ` [PATCH bpf-next 15/17] selftests/bpf: Add tests for callx Alexei Starovoitov
2026-09-24 0:33 ` bot+bpf-ci
2026-09-24 2:13 ` Alexei Starovoitov
2026-09-22 1:13 ` [PATCH bpf-next 16/17] selftests/bpf: Add tests for callx through pointers in read-only data Alexei Starovoitov
2026-09-22 2:01 ` bot+bpf-ci
2026-09-24 0:33 ` bot+bpf-ci
2026-09-22 1:13 ` [PATCH bpf-next 17/17] bpf, docs: Document callx instruction Alexei Starovoitov
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