From patchwork Tue Nov 19 15:34:56 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Valentin Schneider X-Patchwork-Id: 13880159 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (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 EF5D11CCEDF for ; Tue, 19 Nov 2024 15:38:27 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1732030709; cv=none; b=Sd0EuKUAYw7j8cJ9AN2/CDXPQIjA30uPoBzVXkAD/6YAs5npQBqfNUtpuucUwg/QYZIeSTKSj8EMbCoCo91gj+LZSMi39H3wHPaJqPyK1P27o7CCRwmRPnzBt7blfee5e/SACYiaxnpPSpZ11d5iIe2ThIEp2dFePlOhwnqckpo= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1732030709; c=relaxed/simple; bh=HfgzzhQB9Z8CbP30UBBQFA/8juWm49GyqBubPeAUIoY=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=GkGbZ+rbb/NpvZ5smpHsoeo6HDdQdX5r5f43vVn28zxcTSZQnXejHpTptedrHSLrWeSPnHRt6Xj69SvbAF7XPrED5Mbkph8+0SUw1Az4cmik6luQkxfYIC8VWxIWn1Imkw3KnftAyrRxTW0E0mSJM4bLgoICEdproT19joobT7g= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=Piap1QZd; arc=none smtp.client-ip=170.10.129.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="Piap1QZd" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1732030707; 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=bbbl+TXDo+t5kIfzQ14qJGOWt1RDAARb2PWsvxSVw1o=; b=Piap1QZd5jIiEORBIbGNTK9NLlHM+iO/r7rfCfPYmUrnS5q/iIUqSNekaAeetErXSBrrLI TZrOPmYympBWfD/D3NZhF3oM5bw7V7sIozSvXcJBCXZ1+U6yvd6O/t0KkDbN0hwfgF6Zu0 mACt5BPRwg4B9n2MlG805viGa6LWmLo= Received: from mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-593-1WZ3p9jrPQW6G0U5yxmRQQ-1; Tue, 19 Nov 2024 10:38:24 -0500 X-MC-Unique: 1WZ3p9jrPQW6G0U5yxmRQQ-1 X-Mimecast-MFC-AGG-ID: 1WZ3p9jrPQW6G0U5yxmRQQ Received: from mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.4]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id E53F01952D05; Tue, 19 Nov 2024 15:38:14 +0000 (UTC) Received: from vschneid-thinkpadt14sgen2i.remote.csb (unknown [10.39.194.94]) by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id DDE233003B71; Tue, 19 Nov 2024 15:37:59 +0000 (UTC) From: Valentin Schneider To: linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, kvm@vger.kernel.org, linux-mm@kvack.org, bpf@vger.kernel.org, x86@kernel.org, rcu@vger.kernel.org, linux-kselftest@vger.kernel.org Cc: Josh Poimboeuf , Steven Rostedt , Masami Hiramatsu , Jonathan Corbet , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , Paolo Bonzini , Wanpeng Li , Vitaly Kuznetsov , Andy Lutomirski , Peter Zijlstra , Frederic Weisbecker , "Paul E. McKenney" , Neeraj Upadhyay , Joel Fernandes , Josh Triplett , Boqun Feng , Mathieu Desnoyers , Lai Jiangshan , Zqiang , Andrew Morton , Uladzislau Rezki , Christoph Hellwig , Lorenzo Stoakes , Josh Poimboeuf , Jason Baron , Kees Cook , Sami Tolvanen , Ard Biesheuvel , Nicholas Piggin , Juerg Haefliger , Nicolas Saenz Julienne , "Kirill A. Shutemov" , Nadav Amit , Dan Carpenter , Chuang Wang , Yang Jihong , Petr Mladek , "Jason A. Donenfeld" , Song Liu , Julian Pidancet , Tom Lendacky , Dionna Glaze , =?utf-8?q?Thomas_Wei=C3=9Fschuh?= , Juri Lelli , Marcelo Tosatti , Yair Podemsky , Daniel Wagner , Petr Tesarik Subject: [RFC PATCH v3 09/15] objtool: Warn about non __ro_after_init static key usage in .noinstr Date: Tue, 19 Nov 2024 16:34:56 +0100 Message-ID: <20241119153502.41361-10-vschneid@redhat.com> In-Reply-To: <20241119153502.41361-1-vschneid@redhat.com> References: <20241119153502.41361-1-vschneid@redhat.com> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 Later commits will disallow runtime-mutable text in .noinstr sections in order to safely defer instruction patching IPIs. All static keys used in .noinstr sections have now been checked as being either flagged as __ro_after_init, or as forceful static keys. Any occurrence of this new warning would be the result of a code change that will need looking at. Suggested-by: Josh Poimboeuf Signed-off-by: Valentin Schneider --- offset_of(static_key.type) and JUMP_TYPE_FORCEFUL would need to be shoved into a somewhat standalone header file that could be included by objtool itself. --- tools/objtool/Documentation/objtool.txt | 13 ++++++++ tools/objtool/check.c | 41 +++++++++++++++++++++++++ tools/objtool/include/objtool/check.h | 1 + tools/objtool/include/objtool/special.h | 2 ++ tools/objtool/special.c | 3 ++ 5 files changed, 60 insertions(+) diff --git a/tools/objtool/Documentation/objtool.txt b/tools/objtool/Documentation/objtool.txt index 7c3ee959b63c7..06fa285873387 100644 --- a/tools/objtool/Documentation/objtool.txt +++ b/tools/objtool/Documentation/objtool.txt @@ -447,6 +447,19 @@ the objtool maintainers. names and does not use module_init() / module_exit() macros to create them. +13. file.o: warning: func()+0x2a: non __ro_after_init static key "key" in .noinstr section + + This means that the noinstr function func() uses a static key that can be + modified at runtime. This is not allowed as noinstr functions rely on + containing stable instructions after init. + + Check whether the static key in question can really be modified at runtime, + and if it is only enabled during init then mark it as __ro_after_init. If it + genuinely needs to be modified at runtime: + + 1) Directly rely on the underlying atomic count of they key in the noinstr + functions. + 2) Mark the static key as forceful. If the error doesn't seem to make sense, it could be a bug in objtool. Feel free to ask the objtool maintainer for help. diff --git a/tools/objtool/check.c b/tools/objtool/check.c index 00e25492f5065..c1fb02c326839 100644 --- a/tools/objtool/check.c +++ b/tools/objtool/check.c @@ -2056,6 +2056,9 @@ static int add_special_section_alts(struct objtool_file *file) alt->next = orig_insn->alts; orig_insn->alts = alt; + if (special_alt->key_sym) + orig_insn->key_sym = special_alt->key_sym; + list_del(&special_alt->list); free(special_alt); } @@ -3605,6 +3608,41 @@ static int validate_return(struct symbol *func, struct instruction *insn, struct return 0; } +static bool static_key_is_forceful(struct symbol *key) +{ + if (!strcmp(key->sec->name, ".data")) { + unsigned long data_offset = key->sec->data->d_off; + unsigned long key_offset = key->sym.st_value; + char* data = key->sec->data->d_buf; + + /* + * offset_of(static_key.type) + * v + * v JUMP_TYPE_FORCEFUL + * v v + */ + return data[(key_offset + 8) - data_offset] & 0x4; + } + + return false; +} + +static int validate_static_key(struct instruction *insn, struct insn_state *state) +{ + if (state->noinstr && state->instr <= 0) { + if (static_key_is_forceful(insn->key_sym)) + return 0; + + if ((strcmp(insn->key_sym->sec->name, ".data..ro_after_init"))) { + WARN_INSN(insn, "non __ro_after_init static key \"%s\" in .noinstr section", + insn->key_sym->name); + return 1; + } + } + + return 0; +} + static struct instruction *next_insn_to_validate(struct objtool_file *file, struct instruction *insn) { @@ -3766,6 +3804,9 @@ static int validate_branch(struct objtool_file *file, struct symbol *func, if (handle_insn_ops(insn, next_insn, &state)) return 1; + if (insn->key_sym) + validate_static_key(insn, &state); + switch (insn->type) { case INSN_RETURN: diff --git a/tools/objtool/include/objtool/check.h b/tools/objtool/include/objtool/check.h index daa46f1f0965a..35dd21f8f41e1 100644 --- a/tools/objtool/include/objtool/check.h +++ b/tools/objtool/include/objtool/check.h @@ -77,6 +77,7 @@ struct instruction { struct symbol *sym; struct stack_op *stack_ops; struct cfi_state *cfi; + struct symbol *key_sym; }; static inline struct symbol *insn_func(struct instruction *insn) diff --git a/tools/objtool/include/objtool/special.h b/tools/objtool/include/objtool/special.h index 86d4af9c5aa9d..0e61f34fe3a28 100644 --- a/tools/objtool/include/objtool/special.h +++ b/tools/objtool/include/objtool/special.h @@ -27,6 +27,8 @@ struct special_alt { struct section *new_sec; unsigned long new_off; + struct symbol *key_sym; + unsigned int orig_len, new_len; /* group only */ }; diff --git a/tools/objtool/special.c b/tools/objtool/special.c index 097a69db82a0e..fefab2b471bf8 100644 --- a/tools/objtool/special.c +++ b/tools/objtool/special.c @@ -127,6 +127,9 @@ static int get_alt_entry(struct elf *elf, const struct special_entry *entry, return -1; } alt->key_addend = reloc_addend(key_reloc); + + reloc_to_sec_off(key_reloc, &sec, &offset); + alt->key_sym = find_symbol_by_offset(sec, offset & ~3); } return 0;