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Tsirkin" , Jason Wang , Dmitry Fleytman , Akihiko Odaki , Yuri Benditovich Subject: [PATCH v2 2/2] net: mark struct ip_header as QEMU_PACKED Date: Thu, 14 Nov 2024 14:16:19 +0000 Message-Id: <20241114141619.806652-3-peter.maydell@linaro.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20241114141619.806652-1-peter.maydell@linaro.org> References: <20241114141619.806652-1-peter.maydell@linaro.org> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Received-SPF: pass client-ip=2a00:1450:4864:20::336; envelope-from=peter.maydell@linaro.org; helo=mail-wm1-x336.google.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: qemu-devel-bounces+importer=patchew.org@nongnu.org X-ZohoMail-DKIM: pass (identity @linaro.org) X-ZM-MESSAGEID: 1731593843013116600 Content-Type: text/plain; charset="utf-8" The ip_header is not actually guaranteed to be aligned. We attempt to deal with this in some places such as net_checksum_calculate() by using stw_be_p and so on to access the fields, but this is not sufficient to be correct, because even accessing a byte member within an unaligned struct is undefined behaviour. The clang sanitizer will emit warnings like these if net_checksum_calculate() is called: Stopping network: ../../net/checksum.c:106:9: runtime error: member ac= cess within misaligned address 0x556aad9b502e for type 'struct ip_header', = which requires 4 byte alignment 0x556aad9b502e: note: pointer points here 34 56 08 00 45 00 01 48 a5 09 40 00 40 11 7c 8b 0a 00 02 0f 0a 00 0= 2 02 00 44 00 43 01 34 19 56 ^ SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior ../../net/check= sum.c:106:9 in ../../net/checksum.c:106:9: runtime error: load of misaligned address 0= x556aad9b502e for type 'uint8_t' (aka 'unsigned char'), which requires 4 by= te alignment 0x556aad9b502e: note: pointer points here 34 56 08 00 45 00 01 48 a5 09 40 00 40 11 7c 8b 0a 00 02 0f 0a 00 0= 2 02 00 44 00 43 01 34 19 56 ^ Fix this by marking the ip_header struct as QEMU_PACKED, so that the compiler knows that it might be unaligned and will generate the right code for accessing fields. Signed-off-by: Peter Maydell Reviewed-by: Philippe Mathieu-Daud=C3=A9 --- include/net/eth.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/include/net/eth.h b/include/net/eth.h index 3b80b6e07f3..14c34f530fe 100644 --- a/include/net/eth.h +++ b/include/net/eth.h @@ -56,7 +56,7 @@ struct ip_header { uint8_t ip_p; /* protocol */ uint16_t ip_sum; /* checksum */ uint32_t ip_src, ip_dst; /* source and destination address */ -}; +} QEMU_PACKED; =20 typedef struct tcp_header { uint16_t th_sport; /* source port */ --=20 2.34.1