From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 890234E50BB; Tue, 13 Oct 2026 12:22:07 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791894128; cv=none; b=bga6pCl9HVWQxjhd6RhINFUOn9K8as6iJ9lNDQNkFp+wiPmwc0JKzYC+w9DvptKeK1XG/GauWNlnZOxqZi8BADlcGSL1vY1QQSEu6FR8uSV6jkKA3Di+rFPXgFP4Su3dXJs/VPN323KVOYhlHW9FKHbQ4ICF2LBrxiEXsiHhYN8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791894128; c=relaxed/simple; bh=0N/GBDGLHEU3cWOj4ot4Py5kSl1VMWr3BqSY9x72QuI=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=tjQKM2HCu/Mt7tHlyFYYobF60Smq/zKzpLijO57NAKdsPOTLdyH+T1iVvWibLPKzkFAbv1eEwoWkRy1KRt5/R5vMlu68s4kj2dUzErfjumZlB429M7wDdgeQoxP7aOLrb7x1mCUkSmkgqxleXDMa+brm6N4OvxDDJ9atg1ksnVM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=mXcgA073; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="mXcgA073" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E02B51F000FF; Tue, 13 Oct 2026 12:22:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1791894127; bh=R5k+zyR9P2+itOh0gGLw6xSDKKlFGOtTmfEx0CyfpA4=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=mXcgA073kfOa/TtO3Tud0SgGKf32gnSewVw4nmtkZXk43blL+uLq1prUQFTEmiTQX Zg98rgf7nmk1AOj+dBC88luep5Vr2uUSPrPz7s4Mc7Ilotsmh2tCzZJ+20QpTVvXn5 px7S5P1dvk7A5usexAR/10zO5oWOY1SuI06mK7MY= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Yonghong Song , Eduard Zingerman , Leon Hwang , Kumar Kartikeya Dwivedi , Sasha Levin Subject: [PATCH 6.18 456/621] bpf: Reject >8 byte return values on return-reading trampoline paths Date: Tue, 13 Oct 2026 13:37:31 +0200 Message-ID: <20261013112931.654210168@linuxfoundation.org> X-Mailer: git-send-email 2.56.0 In-Reply-To: <20261013112920.855194808@linuxfoundation.org> References: <20261013112920.855194808@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Yonghong Song [ Upstream commit c48796aa6c392cde93946e5d5a9a1f1b1cf72feb ] btf_distill_func_proto() builds the function model used for the fentry/fexit/fmod_ret/fsession trampolines and struct_ops. It has accepted a 16-byte __int128 return value since the trampoline was introduced: __get_type_size() returns the integer's type size, and the return-type check only rejected ret < 0. But the BPF trampoline preserves only 8 bytes of the return value (RAX on x86, i.e. R0). For an attach type that reads the target's return value the second half (RDX / R3) is neither saved nor restored, so a program attached to a function returning a 16-byte value corrupts the value seen by the real caller and itself observes only half of it. struct_ops trampolines have the same limitation. This affects the attach types that read the target's return value: fexit, fmod_ret and fsession (plus the _multi variants of fexit and fsession), and struct_ops. fentry/fentry_multi run before the target returns and are unaffected. Reject a >8 byte return value for these attach types in bpf_check_attach_target() and bpf_check_attach_btf_id_multi(), and for struct_ops in bpf_struct_ops_desc_init(). Fixes: fec56f5890d9 ("bpf: Introduce BPF trampoline") Signed-off-by: Yonghong Song Reviewed-by: Eduard Zingerman Acked-by: Leon Hwang Link: https://lore.kernel.org/bpf/20260729050159.2585809-1-yonghong.song@linux.dev Signed-off-by: Kumar Kartikeya Dwivedi Signed-off-by: Sasha Levin --- kernel/bpf/bpf_struct_ops.c | 12 ++++++++++++ kernel/bpf/verifier.c | 19 +++++++++++++++++++ 2 files changed, 31 insertions(+) diff --git a/kernel/bpf/bpf_struct_ops.c b/kernel/bpf/bpf_struct_ops.c index a41e6730edcf3..472c93b3ff1b6 100644 --- a/kernel/bpf/bpf_struct_ops.c +++ b/kernel/bpf/bpf_struct_ops.c @@ -446,6 +446,18 @@ int bpf_struct_ops_desc_init(struct bpf_struct_ops_desc *st_ops_desc, goto errout; } + /* + * A >8 byte return value is passed back in a register pair, + * which the struct_ops trampoline does not preserve (only + * 8 bytes of the return value are saved and restored). + */ + if (st_ops->func_models[i].ret_size > 8) { + pr_warn("func ptr %s in struct %s has a >8 byte return value, which is not supported\n", + mname, st_ops->name); + err = -EOPNOTSUPP; + goto errout; + } + stub_func_addr = *(void **)(st_ops->cfi_stubs + moff); err = prepare_arg_info(btf, st_ops->name, mname, func_proto, stub_func_addr, diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index d35ac3df9a052..73bebb1078972 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -24101,6 +24101,17 @@ static int check_non_sleepable_error_inject(u32 btf_id) return btf_id_set_contains(&btf_non_sleepable_error_inject, btf_id); } +static bool attach_uses_trampoline_retval(enum bpf_attach_type type) +{ + switch (type) { + case BPF_MODIFY_RETURN: + case BPF_TRACE_FEXIT: + return true; + default: + return false; + } +} + int bpf_check_attach_target(struct bpf_verifier_log *log, const struct bpf_prog *prog, const struct bpf_prog *tgt_prog, @@ -24345,6 +24356,14 @@ int bpf_check_attach_target(struct bpf_verifier_log *log, if (ret < 0) return ret; + if (tgt_info->fmodel.ret_size > 8 && + attach_uses_trampoline_retval(prog->expected_attach_type)) { + bpf_log(log, + "Attach to function %s with a >8 byte return value is not supported for this attach type\n", + tname); + return -EOPNOTSUPP; + } + if (tgt_prog) { if (subprog == 0) addr = (long) tgt_prog->bpf_func; -- 2.53.0