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From: Kees Cook <keescook@chromium.org>
To: linux-hardening@vger.kernel.org
Cc: Kees Cook <keescook@chromium.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>,
	Kalesh Singh <kaleshsingh@google.com>,
	Fuad Tabba <tabba@google.com>,
	Mark Brown <broonie@kernel.org>,
	"Madhavan T. Venkataraman" <madvenka@linux.microsoft.com>,
	Marc Zyngier <maz@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	linux-arm-kernel@lists.infradead.org,
	"Gustavo A. R. Silva" <gustavoars@kernel.org>,
	Bill Wendling <morbo@google.com>,
	Justin Stitt <justinstitt@google.com>,
	linux-kernel@vger.kernel.org
Subject: [PATCH 40/82] arm64: stacktrace: Refactor intentional wrap-around test
Date: Mon, 22 Jan 2024 16:27:15 -0800
Message-Id: <20240123002814.1396804-40-keescook@chromium.org>
In-Reply-To: <20240122235208.work.748-kees@kernel.org>
References: <20240122235208.work.748-kees@kernel.org>
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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: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Kalesh Singh <kaleshsingh@google.com>
Cc: Fuad Tabba <tabba@google.com>
Cc: Mark Brown <broonie@kernel.org>
Cc: "Madhavan T. Venkataraman" <madvenka@linux.microsoft.com>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: linux-arm-kernel@lists.infradead.org
Signed-off-by: Kees Cook <keescook@chromium.org>
---
 arch/arm64/include/asm/stacktrace/common.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/stacktrace/common.h b/arch/arm64/include/asm/stacktrace/common.h
index f63dc654e545..6e0cb84961f8 100644
--- a/arch/arm64/include/asm/stacktrace/common.h
+++ b/arch/arm64/include/asm/stacktrace/common.h
@@ -49,7 +49,7 @@ static inline bool stackinfo_on_stack(const struct stack_info *info,
 	if (!info->low)
 		return false;
 
-	if (sp < info->low || sp + size < sp || sp + size > info->high)
+	if (sp < info->low || add_would_overflow(sp, size) || sp + size > info->high)
 		return false;
 
 	return true;
-- 
2.34.1