linux-hardening - [PATCH 61/82] scsi: mpt3sas: Refactor intentional wrap-around test

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Message-Id: <20240123002814.1396804-61-keescook@chromium.org>
Date: Mon, 22 Jan 2024 16:27:36 -0800
From: Kees Cook <keescook@...omium.org>
To: linux-hardening@...r.kernel.org
Cc: Kees Cook <keescook@...omium.org>,
	Sathya Prakash <sathya.prakash@...adcom.com>,
	Sreekanth Reddy <sreekanth.reddy@...adcom.com>,
	Suganath Prabu Subramani <suganath-prabu.subramani@...adcom.com>,
	"James E.J. Bottomley" <jejb@...ux.ibm.com>,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	MPT-FusionLinux.pdl@...adcom.com,
	linux-scsi@...r.kernel.org,
	"Gustavo A. R. Silva" <gustavoars@...nel.org>,
	Bill Wendling <morbo@...gle.com>,
	Justin Stitt <justinstitt@...gle.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH 61/82] scsi: mpt3sas: Refactor intentional wrap-around test

In an effort to separate intentional arithmetic wrap-around from
unexpected wrap-around, we need to refactor places that depend on this
kind of math. One of the most common code patterns of this is:

	VAR + value < VAR

Notably, this is considered "undefined behavior" for signed and pointer
types, which the kernel works around by using the -fno-strict-overflow
option in the build[1] (which used to just be -fwrapv). Regardless, we
want to get the kernel source to the position where we can meaningfully
instrument arithmetic wrap-around conditions and catch them when they
are unexpected, regardless of whether they are signed[2], unsigned[3],
or pointer[4] types.

Refactor open-coded wrap-around addition test to use add_would_overflow().
This paves the way to enabling the wrap-around sanitizers in the future.

Link: https://git.kernel.org/linus/68df3755e383e6fecf2354a67b08f92f18536594 [1]
Link: https://github.com/KSPP/linux/issues/26 [2]
Link: https://github.com/KSPP/linux/issues/27 [3]
Link: https://github.com/KSPP/linux/issues/344 [4]
Cc: Sathya Prakash <sathya.prakash@...adcom.com>
Cc: Sreekanth Reddy <sreekanth.reddy@...adcom.com>
Cc: Suganath Prabu Subramani <suganath-prabu.subramani@...adcom.com>
Cc: "James E.J. Bottomley" <jejb@...ux.ibm.com>
Cc: "Martin K. Petersen" <martin.petersen@...cle.com>
Cc: MPT-FusionLinux.pdl@...adcom.com
Cc: linux-scsi@...r.kernel.org
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 drivers/scsi/mpt3sas/mpt3sas_ctl.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/scsi/mpt3sas/mpt3sas_ctl.c b/drivers/scsi/mpt3sas/mpt3sas_ctl.c
index 147cb7088d55..b36a9188720f 100644
--- a/drivers/scsi/mpt3sas/mpt3sas_ctl.c
+++ b/drivers/scsi/mpt3sas/mpt3sas_ctl.c
@@ -2382,7 +2382,7 @@ _ctl_diag_read_buffer(struct MPT3SAS_ADAPTER *ioc, void __user *arg)
 			    karg.bytes_to_read));
 
 	/* Truncate data on requests that are too large */
-	if ((diag_data + karg.bytes_to_read < diag_data) ||
+	if ((add_would_overflow(diag_data, karg.bytes_to_read)) ||
 	    (diag_data + karg.bytes_to_read > request_data + request_size))
 		copy_size = request_size - karg.starting_offset;
 	else
-- 
2.34.1