linux-kernel - Re: [PATCH] arm64: kvm: Fix potential overflow in len

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Message-ID: <Z2-j6ZCQbvfNP4z5@linux.dev>
Date: Fri, 27 Dec 2024 23:09:00 -0800
From: Oliver Upton <oliver.upton@...ux.dev>
To: Steven Davis <goldside000@...look.com>
Cc: "maz@...nel.org" <maz@...nel.org>,
	"catalin.marinas@....com" <catalin.marinas@....com>,
	"will@...nel.org" <will@...nel.org>,
	"joey.gouly@....com" <joey.gouly@....com>,
	"suzuki.poulose@....com" <suzuki.poulose@....com>,
	"yuzenghui@...wei.com" <yuzenghui@...wei.com>,
	"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>,
	"kvmarm@...ts.linux.dev" <kvmarm@...ts.linux.dev>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] arm64: kvm: Fix potential overflow in len

On Sat, Dec 28, 2024 at 02:01:27AM +0000, Steven Davis wrote:
> The MMIO sign-extension logic in kvm_handle_mmio_return can
> trigger an integer overflow or undefined behavior when len
> is invalid (e.g., len == 0 or len exceeds the size of unsigned
> long). Specifically, the expression (len * 8) - 1 may result
> in an out-of-bounds shift in the computation of the mask.

I don't believe we need this. len is known to be nonzero and at most 8,
which is already being tested for in the existing condition. See the
definition of kvm_vcpu_dabt_get_as() if you're curious why that is.

-- 
Thanks,
Oliver