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 0B50CBA48 for ; Tue, 7 Mar 2023 18:27:01 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 64E4DC433EF; Tue, 7 Mar 2023 18:27:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1678213620; bh=kXVQvDbRjjHJfJN5vjStph0aXrLR7cljx3xmC6+I7xM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=HUro2UcqKD9LJfaovGK+pksGNmubUtNpe0Msxiejk15kf8Wyiia1G/dwC0tojZq0N VeoQ7uWnqPU+XjEBkgyIlzVdPnxa4eN5xfs1sBz40SH2A2RZ+7KKlkbBSSC8fYFEVb V1E+Mtypx/0X9lemWKPRnOyOmB5PUkfJ8zmGrd4M= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Dave Thaler , Daniel Borkmann , Sasha Levin Subject: [PATCH 6.1 564/885] bpf, docs: Fix modulo zero, division by zero, overflow, and underflow Date: Tue, 7 Mar 2023 17:58:18 +0100 Message-Id: <20230307170026.947355919@linuxfoundation.org> X-Mailer: git-send-email 2.39.2 In-Reply-To: <20230307170001.594919529@linuxfoundation.org> References: <20230307170001.594919529@linuxfoundation.org> User-Agent: quilt/0.67 Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit From: Dave Thaler [ Upstream commit 0eb9d19e2201068260e439a5c96dc85f9f3722a2 ] Fix modulo zero, division by zero, overflow, and underflow. Also clarify how a negative immediate value is used in unsigned division. Signed-off-by: Dave Thaler Signed-off-by: Daniel Borkmann Link: https://lore.kernel.org/bpf/20230124001218.827-1-dthaler1968@googlemail.com Signed-off-by: Sasha Levin --- Documentation/bpf/instruction-set.rst | 16 ++++++++++++++-- 1 file changed, 14 insertions(+), 2 deletions(-) diff --git a/Documentation/bpf/instruction-set.rst b/Documentation/bpf/instruction-set.rst index 5d798437dad47..3ba6475cfbfc7 100644 --- a/Documentation/bpf/instruction-set.rst +++ b/Documentation/bpf/instruction-set.rst @@ -99,19 +99,26 @@ code value description BPF_ADD 0x00 dst += src BPF_SUB 0x10 dst -= src BPF_MUL 0x20 dst \*= src -BPF_DIV 0x30 dst /= src +BPF_DIV 0x30 dst = (src != 0) ? (dst / src) : 0 BPF_OR 0x40 dst \|= src BPF_AND 0x50 dst &= src BPF_LSH 0x60 dst <<= src BPF_RSH 0x70 dst >>= src BPF_NEG 0x80 dst = ~src -BPF_MOD 0x90 dst %= src +BPF_MOD 0x90 dst = (src != 0) ? (dst % src) : dst BPF_XOR 0xa0 dst ^= src BPF_MOV 0xb0 dst = src BPF_ARSH 0xc0 sign extending shift right BPF_END 0xd0 byte swap operations (see `Byte swap instructions`_ below) ======== ===== ========================================================== +Underflow and overflow are allowed during arithmetic operations, meaning +the 64-bit or 32-bit value will wrap. If eBPF program execution would +result in division by zero, the destination register is instead set to zero. +If execution would result in modulo by zero, for ``BPF_ALU64`` the value of +the destination register is unchanged whereas for ``BPF_ALU`` the upper +32 bits of the destination register are zeroed. + ``BPF_ADD | BPF_X | BPF_ALU`` means:: dst_reg = (u32) dst_reg + (u32) src_reg; @@ -128,6 +135,11 @@ BPF_END 0xd0 byte swap operations (see `Byte swap instructions`_ below) src_reg = src_reg ^ imm32 +Also note that the division and modulo operations are unsigned. Thus, for +``BPF_ALU``, 'imm' is first interpreted as an unsigned 32-bit value, whereas +for ``BPF_ALU64``, 'imm' is first sign extended to 64 bits and the result +interpreted as an unsigned 64-bit value. There are no instructions for +signed division or modulo. Byte swap instructions ~~~~~~~~~~~~~~~~~~~~~~ -- 2.39.2