From patchwork Sun Sep 1 13:38:53 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Leon Hwang X-Patchwork-Id: 13786453 X-Patchwork-Delegate: bpf@iogearbox.net Received: from out-178.mta0.migadu.com (out-178.mta0.migadu.com [91.218.175.178]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 54CFA143880 for ; Sun, 1 Sep 2024 13:41:07 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.178 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1725198069; cv=none; b=GHXZlT+MLhT8jOic3Sg6cjRA0xmsA30NQ5FKobLdQ5ItLNoIFwjVt52bo2cRJl/kFWoG7T6IyUlegMmaalDDIDP1zPeKuUZD2d3tq3co6AKSOf1TLRP4AhFHYRlw+VcDbtJnWpHkcZOXq3hkCgnGbhd7FXzXsypPdsev32ZuuzI= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1725198069; c=relaxed/simple; bh=ANyPNj9nDVgRBY78OaPZekGNmr78hQPSczgo96lUxqA=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=jB/eAUyPPH/xLQxaaHTZw8JmXJyl9EH6fD3UHb7/sTRXOe3aZIxgzxckNTROzwhWTnYhjO0NznjBU1qdeMR5UA7s6VIX79pxuJ32D9eHSi0y1btAgALR0XKP5qJFYE0BrSa91VulXe7Hgvl8fMIhKd5IW1mToqWMlGFHoRaYbnQ= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=bw/TqWKk; arc=none smtp.client-ip=91.218.175.178 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="bw/TqWKk" X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1725198062; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=8HCqzwOX+eH0kqWdRTP/yCjOIus8cQ72D7HFP04MvtA=; b=bw/TqWKkg2e/XcKO3lIZnsOsIM7buVIfxjiki8t9LQw2qBB0vnvGBgUOfUHSgVZOwXL1Zd kKVs6yOqPI3OeMNemSkYv3jJdUIB0zHOAUuaOh5eehlH5+Usm75nW0/oq9bR4Rzogkylcp uaHnMQgk+vK+bRDGr625PIAM+GaAzEU= From: Leon Hwang To: bpf@vger.kernel.org Cc: ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, toke@redhat.com, martin.lau@kernel.org, yonghong.song@linux.dev, puranjay@kernel.org, xukuohai@huaweicloud.com, eddyz87@gmail.com, iii@linux.ibm.com, leon.hwang@linux.dev, kernel-patches-bot@fb.com Subject: [PATCH bpf-next v2 1/4] bpf, x64: Fix tailcall infinite loop caused by freplace Date: Sun, 1 Sep 2024 21:38:53 +0800 Message-ID: <20240901133856.64367-2-leon.hwang@linux.dev> In-Reply-To: <20240901133856.64367-1-leon.hwang@linux.dev> References: <20240901133856.64367-1-leon.hwang@linux.dev> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Migadu-Flow: FLOW_OUT X-Patchwork-Delegate: bpf@iogearbox.net This patch fixes a tailcall infinite loop issue caused by freplace. Since commit 1c123c567fb1 ("bpf: Resolve fext program type when checking map compatibility"), freplace prog is allowed to tail call its target prog. Then, when a freplace prog attaches to its target prog's subprog and tail calls its target prog, kernel will panic. For example: tc_bpf2bpf.c: // SPDX-License-Identifier: GPL-2.0 \#include \#include __noinline int subprog_tc(struct __sk_buff *skb) { return skb->len * 2; } SEC("tc") int entry_tc(struct __sk_buff *skb) { return subprog_tc(skb); } char __license[] SEC("license") = "GPL"; tailcall_bpf2bpf_hierarchy_freplace.c: // SPDX-License-Identifier: GPL-2.0 \#include \#include struct { __uint(type, BPF_MAP_TYPE_PROG_ARRAY); __uint(max_entries, 1); __uint(key_size, sizeof(__u32)); __uint(value_size, sizeof(__u32)); } jmp_table SEC(".maps"); int count = 0; static __noinline int subprog_tail(struct __sk_buff *skb) { bpf_tail_call_static(skb, &jmp_table, 0); return 0; } SEC("freplace") int entry_freplace(struct __sk_buff *skb) { count++; subprog_tail(skb); subprog_tail(skb); return count; } char __license[] SEC("license") = "GPL"; The attach target of entry_freplace is subprog_tc, and the tail callee in subprog_tail is entry_tc. Then, the infinite loop will be entry_tc -> subprog_tc -> entry_freplace -> subprog_tail --tailcall-> entry_tc, because tail_call_cnt in entry_freplace will count from zero for every time of entry_freplace execution. Kernel will panic: [ 15.310490] BUG: TASK stack guard page was hit at (____ptrval____) (stack is (____ptrval____)..(____ptrval____)) [ 15.310490] Oops: stack guard page: 0000 [#1] PREEMPT SMP NOPTI [ 15.310490] CPU: 1 PID: 89 Comm: test_progs Tainted: G OE 6.10.0-rc6-g026dcdae8d3e-dirty #72 [ 15.310490] Hardware name: QEMU Ubuntu 24.04 PC (i440FX + PIIX, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014 [ 15.310490] RIP: 0010:bpf_prog_3a140cef239a4b4f_subprog_tail+0x14/0x53 [ 15.310490] Code: cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc f3 0f 1e fa 0f 1f 44 00 00 0f 1f 00 55 48 89 e5 f3 0f 1e fa <50> 50 53 41 55 48 89 fb 49 bd 00 2a 46 82 98 9c ff ff 48 89 df 4c [ 15.310490] RSP: 0018:ffffb500c0aa0000 EFLAGS: 00000202 [ 15.310490] RAX: ffffb500c0aa0028 RBX: ffff9c98808b7e00 RCX: 0000000000008cb5 [ 15.310490] RDX: 0000000000000000 RSI: ffff9c9882462a00 RDI: ffff9c98808b7e00 [ 15.310490] RBP: ffffb500c0aa0000 R08: 0000000000000000 R09: 0000000000000000 [ 15.310490] R10: 0000000000000001 R11: 0000000000000000 R12: ffffb500c01af000 [ 15.310490] R13: ffffb500c01cd000 R14: 0000000000000000 R15: 0000000000000000 [ 15.310490] FS: 00007f133b665140(0000) GS:ffff9c98bbd00000(0000) knlGS:0000000000000000 [ 15.310490] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 15.310490] CR2: ffffb500c0a9fff8 CR3: 0000000102478000 CR4: 00000000000006f0 [ 15.310490] Call Trace: [ 15.310490] <#DF> [ 15.310490] ? die+0x36/0x90 [ 15.310490] ? handle_stack_overflow+0x4d/0x60 [ 15.310490] ? exc_double_fault+0x117/0x1a0 [ 15.310490] ? asm_exc_double_fault+0x23/0x30 [ 15.310490] ? bpf_prog_3a140cef239a4b4f_subprog_tail+0x14/0x53 [ 15.310490] [ 15.310490] [ 15.310490] bpf_prog_85781a698094722f_entry+0x4c/0x64 [ 15.310490] bpf_prog_1c515f389a9059b4_entry2+0x19/0x1b [ 15.310490] ... [ 15.310490] bpf_prog_85781a698094722f_entry+0x4c/0x64 [ 15.310490] bpf_prog_1c515f389a9059b4_entry2+0x19/0x1b [ 15.310490] bpf_test_run+0x210/0x370 [ 15.310490] ? bpf_test_run+0x128/0x370 [ 15.310490] bpf_prog_test_run_skb+0x388/0x7a0 [ 15.310490] __sys_bpf+0xdbf/0x2c40 [ 15.310490] ? clockevents_program_event+0x52/0xf0 [ 15.310490] ? lock_release+0xbf/0x290 [ 15.310490] __x64_sys_bpf+0x1e/0x30 [ 15.310490] do_syscall_64+0x68/0x140 [ 15.310490] entry_SYSCALL_64_after_hwframe+0x76/0x7e [ 15.310490] RIP: 0033:0x7f133b52725d [ 15.310490] Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 90 f3 0f 1e fa 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 8b bb 0d 00 f7 d8 64 89 01 48 [ 15.310490] RSP: 002b:00007ffddbc10258 EFLAGS: 00000206 ORIG_RAX: 0000000000000141 [ 15.310490] RAX: ffffffffffffffda RBX: 00007ffddbc10828 RCX: 00007f133b52725d [ 15.310490] RDX: 0000000000000050 RSI: 00007ffddbc102a0 RDI: 000000000000000a [ 15.310490] RBP: 00007ffddbc10270 R08: 0000000000000000 R09: 00007ffddbc102a0 [ 15.310490] R10: 0000000000000064 R11: 0000000000000206 R12: 0000000000000004 [ 15.310490] R13: 0000000000000000 R14: 0000558ec4c24890 R15: 00007f133b6ed000 [ 15.310490] [ 15.310490] Modules linked in: bpf_testmod(OE) [ 15.310490] ---[ end trace 0000000000000000 ]--- [ 15.310490] RIP: 0010:bpf_prog_3a140cef239a4b4f_subprog_tail+0x14/0x53 [ 15.310490] Code: cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc f3 0f 1e fa 0f 1f 44 00 00 0f 1f 00 55 48 89 e5 f3 0f 1e fa <50> 50 53 41 55 48 89 fb 49 bd 00 2a 46 82 98 9c ff ff 48 89 df 4c [ 15.310490] RSP: 0018:ffffb500c0aa0000 EFLAGS: 00000202 [ 15.310490] RAX: ffffb500c0aa0028 RBX: ffff9c98808b7e00 RCX: 0000000000008cb5 [ 15.310490] RDX: 0000000000000000 RSI: ffff9c9882462a00 RDI: ffff9c98808b7e00 [ 15.310490] RBP: ffffb500c0aa0000 R08: 0000000000000000 R09: 0000000000000000 [ 15.310490] R10: 0000000000000001 R11: 0000000000000000 R12: ffffb500c01af000 [ 15.310490] R13: ffffb500c01cd000 R14: 0000000000000000 R15: 0000000000000000 [ 15.310490] FS: 00007f133b665140(0000) GS:ffff9c98bbd00000(0000) knlGS:0000000000000000 [ 15.310490] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 15.310490] CR2: ffffb500c0a9fff8 CR3: 0000000102478000 CR4: 00000000000006f0 [ 15.310490] Kernel panic - not syncing: Fatal exception in interrupt [ 15.310490] Kernel Offset: 0x30000000 from 0xffffffff81000000 (relocation range: 0xffffffff80000000-0xffffffffbfffffff) This patch fixes the issue by initializing tail_call_cnt at the prologue of entry_tc. Next, when call subprog_tc, the tail_call_cnt_ptr is propagated to subprog_tc by rax. Next, when jump to entry_freplace, the tail_call_cnt_ptr will be reused to count tailcall in freplace prog. Next, when call subprog_tail, the tail_call_cnt_ptr is propagated to subprog_tail by rax. Next, while tail calling to entry_tc, the tail_call_cnt on the stack of entry_tc increments via the tail_call_cnt_ptr. The whole procedure shows as the following JITed prog dumping. bpftool p d j n entry_tc: int entry_tc(struct __sk_buff * skb): bpf_prog_1c515f389a9059b4_entry_tc: ; return subprog_tc(skb); 0: endbr64 4: xorq %rax, %rax ;; rax = 0 (tail_call_cnt) 7: nopl (%rax,%rax) c: pushq %rbp d: movq %rsp, %rbp 10: endbr64 14: cmpq $33, %rax ;; if rax > 33, rax = tcc_ptr 18: ja 0x20 ;; if rax > 33 goto 0x20 ---+ 1a: pushq %rax ;; [rbp - 8] = rax = 0 | 1b: movq %rsp, %rax ;; rax = rbp - 8 | 1e: jmp 0x21 ;; ---------+ | 20: pushq %rax ;; <--------|---------------+ 21: pushq %rax ;; <--------+ [rbp - 16] = rax 22: movq -16(%rbp), %rax ;; rax = tcc_ptr 29: callq 0x70 ;; call subprog_tc() ; return subprog_tc(skb); 2e: leave 2f: retq int subprog_tc(struct __sk_buff * skb): bpf_prog_1e8f76e2374a0607_subprog_tc: ; return skb->len * 2; 0: endbr64 4: nopl (%rax) ;; do not touch tail_call_cnt 7: jmp 0x108 ;; jump to entry_freplace() c: pushq %rbp d: movq %rsp, %rbp 10: endbr64 14: pushq %rax 15: pushq %rax 16: movl 112(%rdi), %eax ; return skb->len * 2; 19: shll %eax ; return skb->len * 2; 1b: leave 1c: retq bpftool p d j n entry_freplace: int entry_freplace(struct __sk_buff * skb): bpf_prog_85781a698094722f_entry_freplace: ; int entry_freplace(struct __sk_buff *skb) 0: endbr64 4: nopl (%rax) ;; do not touch tail_call_cnt 7: nopl (%rax,%rax) c: pushq %rbp d: movq %rsp, %rbp 10: endbr64 14: cmpq $33, %rax ;; if rax > 33, rax = tcc_ptr 18: ja 0x20 ;; if rax > 33 goto 0x20 ---+ 1a: pushq %rax ;; [rbp - 8] = rax = 0 | 1b: movq %rsp, %rax ;; rax = rbp - 8 | 1e: jmp 0x21 ;; ---------+ | 20: pushq %rax ;; <--------|---------------+ 21: pushq %rax ;; <--------+ [rbp - 16] = rax 22: pushq %rbx ;; callee saved 23: pushq %r13 ;; callee saved 25: movq %rdi, %rbx ;; rbx = skb (callee saved) ; count++; 28: movabsq $-123406219759616, %r13 32: movl (%r13), %edi 36: addl $1, %edi 39: movl %edi, (%r13) ; subprog_tail(skb); 3d: movq %rbx, %rdi ;; rdi = skb 40: movq -16(%rbp), %rax ;; rax = tcc_ptr 47: callq 0x80 ;; call subprog_tail() ; subprog_tail(skb); 4c: movq %rbx, %rdi ;; rdi = skb 4f: movq -16(%rbp), %rax ;; rax = tcc_ptr 56: callq 0x80 ;; call subprog_tail() ; return count; 5b: movl (%r13), %eax ; return count; 5f: popq %r13 61: popq %rbx 62: leave 63: retq int subprog_tail(struct __sk_buff * skb): bpf_prog_3a140cef239a4b4f_subprog_tail: ; int subprog_tail(struct __sk_buff *skb) 0: endbr64 4: nopl (%rax) ;; do not touch tail_call_cnt 7: nopl (%rax,%rax) c: pushq %rbp d: movq %rsp, %rbp 10: endbr64 14: pushq %rax ;; [rbp - 8] = rax (tcc_ptr) 15: pushq %rax ;; [rbp - 16] = rax (tcc_ptr) 16: pushq %rbx ;; callee saved 17: pushq %r13 ;; callee saved 19: movq %rdi, %rbx ;; rbx = skb ; asm volatile("r1 = %[ctx]\n\t" 1c: movabsq $-128494642337280, %r13 ;; r13 = jmp_table 26: movq %rbx, %rdi ;; 1st arg, skb 29: movq %r13, %rsi ;; 2nd arg, jmp_table 2c: xorl %edx, %edx ;; 3rd arg, index = 0 2e: movq -16(%rbp), %rax ;; rax = [rbp - 16] (tcc_ptr) 35: cmpq $33, (%rax) 39: jae 0x4e ;; if *tcc_ptr >= 33 goto 0x4e --------+ 3b: nopl (%rax,%rax) ;; jmp bypass, toggled by poking | 40: addq $1, (%rax) ;; (*tcc_ptr)++ | 44: popq %r13 ;; callee saved | 46: popq %rbx ;; callee saved | 47: popq %rax ;; undo rbp-16 push | 48: popq %rax ;; undo rbp-8 push | 49: jmp 0xfffffffffffffe18 ;; tail call target, toggled by poking | ; return 0; ;; | 4e: popq %r13 ;; restore callee saved <--------------+ 50: popq %rbx ;; restore callee saved 51: leave 52: retq As a result, the tail_call_cnt is stored on the stack of entry_tc. And the tail_call_cnt_ptr is propagated between subprog_tc, entry_freplace, subprog_tail and entry_tc. But wait, what if entry_freplace has tailcall and entry_tc has no tailcall? It's to disallow attaching this entry_freplace to this entry_tc in verifier. And, what if entry_freplace has tailcall and entry_tc has tailcall and entry_freplace attaches to entry_tc? In this patch, the tailcall info of entry_freplace inherits from its target. Therefore, it swaps the positions of nop5 and xor/nop3 in order to initialize tail_call_cnt at the prologue of entry_tc and then propagate the tail_call_cnt to entry_freplace. Fixes: 1c123c567fb1 ("bpf: Resolve fext program type when checking map compatibility") Signed-off-by: Leon Hwang --- arch/x86/net/bpf_jit_comp.c | 26 ++++++++++++++++++-------- kernel/bpf/verifier.c | 6 ++++++ 2 files changed, 24 insertions(+), 8 deletions(-) diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c index 074b41fafbe3f..143974b3e953b 100644 --- a/arch/x86/net/bpf_jit_comp.c +++ b/arch/x86/net/bpf_jit_comp.c @@ -274,6 +274,8 @@ struct jit_context { #define X86_PATCH_SIZE 5 /* Number of bytes that will be skipped on tailcall */ #define X86_TAIL_CALL_OFFSET (12 + ENDBR_INSN_SIZE) +/* Number of extra bytes that will be skipped on poke */ +#define X86_POKE_EXTRA 3 static void push_r12(u8 **pprog) { @@ -441,17 +443,13 @@ static void emit_prologue_tail_call(u8 **pprog, bool is_subprog) */ static void emit_prologue(u8 **pprog, u32 stack_depth, bool ebpf_from_cbpf, bool tail_call_reachable, bool is_subprog, - bool is_exception_cb) + bool is_exception_cb, bool is_extension) { u8 *prog = *pprog; emit_cfi(&prog, is_subprog ? cfi_bpf_subprog_hash : cfi_bpf_hash); - /* BPF trampoline can be made to work without these nops, - * but let's waste 5 bytes for now and optimize later - */ - emit_nops(&prog, X86_PATCH_SIZE); if (!ebpf_from_cbpf) { - if (tail_call_reachable && !is_subprog) + if (tail_call_reachable && !is_extension && !is_subprog) /* When it's the entry of the whole tailcall context, * zeroing rax means initialising tail_call_cnt. */ @@ -460,6 +458,10 @@ static void emit_prologue(u8 **pprog, u32 stack_depth, bool ebpf_from_cbpf, /* Keep the same instruction layout. */ emit_nops(&prog, 3); /* nop3 */ } + /* BPF trampoline can be made to work without these nops, + * but let's waste 5 bytes for now and optimize later + */ + emit_nops(&prog, X86_PATCH_SIZE); /* Exception callback receives FP as third parameter */ if (is_exception_cb) { EMIT3(0x48, 0x89, 0xF4); /* mov rsp, rsi */ @@ -573,10 +575,13 @@ int bpf_arch_text_poke(void *ip, enum bpf_text_poke_type t, /* * See emit_prologue(), for IBT builds the trampoline hook is preceded - * with an ENDBR instruction. + * with an ENDBR instruction and 3 bytes tail_call_cnt initialization + * instruction. */ if (is_endbr(*(u32 *)ip)) ip += ENDBR_INSN_SIZE; + if (is_bpf_text_address((long)ip)) + ip += X86_POKE_EXTRA; return __bpf_arch_text_poke(ip, t, old_addr, new_addr); } @@ -1366,6 +1371,7 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image, u8 *rw_image int oldproglen, struct jit_context *ctx, bool jmp_padding) { bool tail_call_reachable = bpf_prog->aux->tail_call_reachable; + bool is_extension = bpf_prog->type == BPF_PROG_TYPE_EXT; struct bpf_insn *insn = bpf_prog->insnsi; bool callee_regs_used[4] = {}; int insn_cnt = bpf_prog->len; @@ -1384,7 +1390,8 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image, u8 *rw_image emit_prologue(&prog, bpf_prog->aux->stack_depth, bpf_prog_was_classic(bpf_prog), tail_call_reachable, - bpf_is_subprog(bpf_prog), bpf_prog->aux->exception_cb); + bpf_is_subprog(bpf_prog), bpf_prog->aux->exception_cb, + is_extension); /* Exception callback will clobber callee regs for its own use, and * restore the original callee regs from main prog's stack frame. */ @@ -2923,6 +2930,8 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *rw_im */ if (is_endbr(*(u32 *)orig_call)) orig_call += ENDBR_INSN_SIZE; + if (is_bpf_text_address((long)orig_call)) + orig_call += X86_POKE_EXTRA; orig_call += X86_PATCH_SIZE; } @@ -3025,6 +3034,7 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *rw_im /* remember return value in a stack for bpf prog to access */ emit_stx(&prog, BPF_DW, BPF_REG_FP, BPF_REG_0, -8); im->ip_after_call = image + (prog - (u8 *)rw_image); + emit_nops(&prog, X86_POKE_EXTRA); emit_nops(&prog, X86_PATCH_SIZE); } diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 217eb0eafa2a6..0a92fd4e0401e 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -21898,6 +21898,12 @@ int bpf_check_attach_target(struct bpf_verifier_log *log, bpf_log(log, "Cannot extend fentry/fexit\n"); return -EINVAL; } + if (prog_extension && prog->aux->tail_call_reachable && + !(aux->func ? aux->func[subprog]->aux->tail_call_reachable : + aux->tail_call_reachable)) { + bpf_log(log, "Cannot extend no-tailcall target with tailcall ext prog\n"); + return -EINVAL; + } } else { if (prog_extension) { bpf_log(log, "Cannot replace kernel functions\n");