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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id q19-20020aa79833000000b00540c3b6f32fsm7128298pfl.49.2022.09.23.20.07.43 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 23 Sep 2022 20:07:43 -0700 (PDT) From: Kees Cook To: "K. Y. Srinivasan" Cc: Kees Cook , Haiyang Zhang , Stephen Hemminger , Wei Liu , Dexuan Cui , linux-hyperv@vger.kernel.org, Nathan Chancellor , "Gustavo A. R. Silva" , linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org Subject: [PATCH] Drivers: hv: vmbus: Split memcpy of flex-array Date: Fri, 23 Sep 2022 20:07:41 -0700 Message-Id: <20220924030741.3345349-1-keescook@chromium.org> X-Mailer: git-send-email 2.34.1 MIME-Version: 1.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=1726; h=from:subject; bh=7+JpelBNpq5Fw7aAx9OdfzO7liLVsPVR9WciMS4r/NU=; b=owEBbQKS/ZANAwAKAYly9N/cbcAmAcsmYgBjLnR9wwp6bolWrhQnItcWX3Mum1QtC8G4uZsAS92B C8WkhqaJAjMEAAEKAB0WIQSlw/aPIp3WD3I+bhOJcvTf3G3AJgUCYy50fQAKCRCJcvTf3G3AJpIbD/ 4o9CL5W3GD7T8nYy9vURy0GTTRdPcnwfkEBkvSaBS+6Z047JJXm6JqxYu/4Lj0AMUpOilsKpZIcNXl R6Fro9YcKKMxsPodqIQAc/OFDFje/l3feGhMAHiETi/a5uErOeUJ2MjdCNa5AHSbiaEcB/Es7qj83K DRp14VcgSN5krKbp/6hzYptKDoOt1B0Tf6pGwecGCVT+x/Hphs5UT6pqGhlCsmArMSAI4peTWppE17 fhKWhEmQQDcPquyhachSwTqTdXtCd1XaluRb3veUn6hRKIjC90NamtF8DTyNPMo7LAbnpHj4ydrRR2 FzP5KnEnTTd1xPt3KZ9aAIkZluItICRn/hqfNPCgv5ZsZ0Ynqwn3b9/JWOCOJNxvUwavjeLswrCgmS Lw6nffnf55NJCKMDWgptuaynCK1RMelbVckcZTasi88pRe0zhsRnC5LNad/z8SzY44y7ry5r9Lha5o LFlw3gW16kUMMgUamMJh8SPz+P4JhPTQUUY/yVC6jSsaNbvHicYHFsLBn2XCLveCpBZAYOyNWfYaj4 uYgO8LgNb1aedi4QQ3qaCyVBrjmlPqWqH336vwOA3yaxn8WiippB5r+wH+inl4MwIsG2Dj78qimr1T U4yM40JKYUupXDXYiB5ZUNYZnEV9aC9dcpEQA3ibZ+WuJOfIwgCZjnFc7pCw== X-Developer-Key: i=keescook@chromium.org; a=openpgp; fpr=A5C3F68F229DD60F723E6E138972F4DFDC6DC026 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" To work around a misbehavior of the compiler's ability to see into composite flexible array structs (as detailed in the coming memcpy() hardening series[1]), split the memcpy() of the header and the payload so no false positive run-time overflow warning will be generated. As it turns out, this appears to actually reduce the text size: $ size drivers/hv/vmbus_drv.o.before drivers/hv/vmbus_drv.o text data bss dec hex filename 22968 5239 232 28439 6f17 drivers/hv/vmbus_drv.o.before 23032 5239 232 28503 6f57 drivers/hv/vmbus_drv.o [1] https://lore.kernel.org/linux-hardening/20220901065914.1417829-2-keesco= ok@chromium.org/ Cc: "K. Y. Srinivasan" Cc: Haiyang Zhang Cc: Stephen Hemminger Cc: Wei Liu Cc: Dexuan Cui Cc: linux-hyperv@vger.kernel.org Reported-by: Nathan Chancellor Reported-by: "Gustavo A. R. Silva" Signed-off-by: Kees Cook Reviewed-by: Gustavo A. R. Silva Tested-by: Nathan Chancellor --- drivers/hv/vmbus_drv.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c index 23c680d1a0f5..9b111a8262e3 100644 --- a/drivers/hv/vmbus_drv.c +++ b/drivers/hv/vmbus_drv.c @@ -1131,7 +1131,8 @@ void vmbus_on_msg_dpc(unsigned long data) return; =20 INIT_WORK(&ctx->work, vmbus_onmessage_work); - memcpy(&ctx->msg, &msg_copy, sizeof(msg->header) + payload_size); + ctx->msg.header =3D msg_copy.header; + memcpy(&ctx->msg.payload, msg_copy.u.payload, payload_size); =20 /* * The host can generate a rescind message while we --=20 2.34.1