From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 EEE1627CCC7; Wed, 23 Apr 2025 15:16:21 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1745421382; cv=none; b=m7vhHprKrWC2MXweIWtZhBfijvjTKCq4PoeR/Ttqtaqrg0VgioYdScZ0BaeyFV5qFxC1ZLBrtsfGkLiyHa0dvb0Pxayb07rjNFCXqJS5EgZ+akgE5CJ3e0t8I+NpjIy16Jbu4o02trR2uEMteTI8BO+niiQqyXmTGBgNJBcVJNw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1745421382; c=relaxed/simple; bh=8fg7TNmoO0ppj8v6xntVWLEaZtBCc9+Hbxo84MWEx+o=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=DpItHyy1sxEh2YjQ50CLfrJycTtTzoGs1wPCnoTH4zMyLA/g8HiqToiINU52IiAj0IH2VcSXH8uO2T6qkpT6Mt5WlfkPvjl4Tf1pObuhQix8S38LYblJbo6gWVw8vgsX68V+kHOTDKuM6POwbBepntOdB0coH1F1dPkvkZMOe74= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=KSLKVu02; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="KSLKVu02" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0F173C4CEE3; Wed, 23 Apr 2025 15:16:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1745421381; bh=8fg7TNmoO0ppj8v6xntVWLEaZtBCc9+Hbxo84MWEx+o=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=KSLKVu020eAiiQPpRS/nSnnMf3BCoUrUnrLCr6SNJZYDJGXzROJZibC6Vti1GqPf7 fFp3M0EeBxbJaofM6uVBs7BcgS50d8mASyYGDOxbqIzalgYBzrQjgfHy1YLZbgucaW cxV0+3FReuGs/hRi2gU1cYwtw14o1jy/955CjT2s= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Nick Zavaritsky , Eduard Zingerman , Alexei Starovoitov , Shung-Hsi Yu Subject: [PATCH 6.12 216/223] bpf: track changes_pkt_data property for global functions Date: Wed, 23 Apr 2025 16:44:48 +0200 Message-ID: <20250423142625.964938108@linuxfoundation.org> X-Mailer: git-send-email 2.49.0 In-Reply-To: <20250423142617.120834124@linuxfoundation.org> References: <20250423142617.120834124@linuxfoundation.org> User-Agent: quilt/0.68 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.12-stable review patch. If anyone has any objections, please let me know. ------------------ From: Eduard Zingerman commit 51081a3f25c742da5a659d7fc6fd77ebfdd555be upstream. When processing calls to certain helpers, verifier invalidates all packet pointers in a current state. For example, consider the following program: __attribute__((__noinline__)) long skb_pull_data(struct __sk_buff *sk, __u32 len) { return bpf_skb_pull_data(sk, len); } SEC("tc") int test_invalidate_checks(struct __sk_buff *sk) { int *p = (void *)(long)sk->data; if ((void *)(p + 1) > (void *)(long)sk->data_end) return TCX_DROP; skb_pull_data(sk, 0); *p = 42; return TCX_PASS; } After a call to bpf_skb_pull_data() the pointer 'p' can't be used safely. See function filter.c:bpf_helper_changes_pkt_data() for a list of such helpers. At the moment verifier invalidates packet pointers when processing helper function calls, and does not traverse global sub-programs when processing calls to global sub-programs. This means that calls to helpers done from global sub-programs do not invalidate pointers in the caller state. E.g. the program above is unsafe, but is not rejected by verifier. This commit fixes the omission by computing field bpf_subprog_info->changes_pkt_data for each sub-program before main verification pass. changes_pkt_data should be set if: - subprogram calls helper for which bpf_helper_changes_pkt_data returns true; - subprogram calls a global function, for which bpf_subprog_info->changes_pkt_data should be set. The verifier.c:check_cfg() pass is modified to compute this information. The commit relies on depth first instruction traversal done by check_cfg() and absence of recursive function calls: - check_cfg() would eventually visit every call to subprogram S in a state when S is fully explored; - when S is fully explored: - every direct helper call within S is explored (and thus changes_pkt_data is set if needed); - every call to subprogram S1 called by S was visited with S1 fully explored (and thus S inherits changes_pkt_data from S1). The downside of such approach is that dead code elimination is not taken into account: if a helper call inside global function is dead because of current configuration, verifier would conservatively assume that the call occurs for the purpose of the changes_pkt_data computation. Reported-by: Nick Zavaritsky Closes: https://lore.kernel.org/bpf/0498CA22-5779-4767-9C0C-A9515CEA711F@gmail.com/ Signed-off-by: Eduard Zingerman Link: https://lore.kernel.org/r/20241210041100.1898468-4-eddyz87@gmail.com Signed-off-by: Alexei Starovoitov Signed-off-by: Shung-Hsi Yu Signed-off-by: Greg Kroah-Hartman --- include/linux/bpf_verifier.h | 1 + kernel/bpf/verifier.c | 32 +++++++++++++++++++++++++++++++- 2 files changed, 32 insertions(+), 1 deletion(-) --- a/include/linux/bpf_verifier.h +++ b/include/linux/bpf_verifier.h @@ -668,6 +668,7 @@ struct bpf_subprog_info { bool args_cached: 1; /* true if bpf_fastcall stack region is used by functions that can't be inlined */ bool keep_fastcall_stack: 1; + bool changes_pkt_data: 1; u8 arg_cnt; struct bpf_subprog_arg_info args[MAX_BPF_FUNC_REG_ARGS]; --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -9831,6 +9831,8 @@ static int check_func_call(struct bpf_ve verbose(env, "Func#%d ('%s') is global and assumed valid.\n", subprog, sub_name); + if (env->subprog_info[subprog].changes_pkt_data) + clear_all_pkt_pointers(env); /* mark global subprog for verifying after main prog */ subprog_aux(env, subprog)->called = true; clear_caller_saved_regs(env, caller->regs); @@ -16021,6 +16023,29 @@ enforce_retval: return 0; } +static void mark_subprog_changes_pkt_data(struct bpf_verifier_env *env, int off) +{ + struct bpf_subprog_info *subprog; + + subprog = find_containing_subprog(env, off); + subprog->changes_pkt_data = true; +} + +/* 't' is an index of a call-site. + * 'w' is a callee entry point. + * Eventually this function would be called when env->cfg.insn_state[w] == EXPLORED. + * Rely on DFS traversal order and absence of recursive calls to guarantee that + * callee's change_pkt_data marks would be correct at that moment. + */ +static void merge_callee_effects(struct bpf_verifier_env *env, int t, int w) +{ + struct bpf_subprog_info *caller, *callee; + + caller = find_containing_subprog(env, t); + callee = find_containing_subprog(env, w); + caller->changes_pkt_data |= callee->changes_pkt_data; +} + /* non-recursive DFS pseudo code * 1 procedure DFS-iterative(G,v): * 2 label v as discovered @@ -16154,6 +16179,7 @@ static int visit_func_call_insn(int t, s bool visit_callee) { int ret, insn_sz; + int w; insn_sz = bpf_is_ldimm64(&insns[t]) ? 2 : 1; ret = push_insn(t, t + insn_sz, FALLTHROUGH, env); @@ -16165,8 +16191,10 @@ static int visit_func_call_insn(int t, s mark_jmp_point(env, t + insn_sz); if (visit_callee) { + w = t + insns[t].imm + 1; mark_prune_point(env, t); - ret = push_insn(t, t + insns[t].imm + 1, BRANCH, env); + merge_callee_effects(env, t, w); + ret = push_insn(t, w, BRANCH, env); } return ret; } @@ -16486,6 +16514,8 @@ static int visit_insn(int t, struct bpf_ mark_prune_point(env, t); mark_jmp_point(env, t); } + if (bpf_helper_call(insn) && bpf_helper_changes_pkt_data(insn->imm)) + mark_subprog_changes_pkt_data(env, t); if (insn->src_reg == BPF_PSEUDO_KFUNC_CALL) { struct bpf_kfunc_call_arg_meta meta;