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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id p126sm4144367pfb.32.2021.04.23.02.03.50 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 23 Apr 2021 02:03:51 -0700 (PDT) Date: Fri, 23 Apr 2021 02:03:50 -0700 From: Kees Cook To: Thomas Gleixner Cc: Greg Kroah-Hartman , linux-kernel@vger.kernel.org, Aditya Pakki , kjlu@umn.edu, Borislav Petkov , "H. Peter Anvin" , Joe Perches , Nicolai Stange , Roland Dreier Subject: Re: [PATCH 113/190] Revert "x86/hpet: Prevent potential NULL pointer dereference" Message-ID: <202104230201.EEB997CD8@keescook> References: <20210421130105.1226686-1-gregkh@linuxfoundation.org> <20210421130105.1226686-114-gregkh@linuxfoundation.org> <202104211245.F5FEC8D15D@keescook> <87im4dx5cc.ffs@nanos.tec.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87im4dx5cc.ffs@nanos.tec.linutronix.de> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Apr 23, 2021 at 01:33:07AM +0200, Thomas Gleixner wrote: > On Wed, Apr 21 2021 at 12:49, Kees Cook wrote: > > On Wed, Apr 21, 2021 at 02:59:48PM +0200, Greg Kroah-Hartman wrote: > >> diff --git a/arch/x86/kernel/hpet.c b/arch/x86/kernel/hpet.c > >> index 08651a4e6aa0..0515a97bf6f5 100644 > >> --- a/arch/x86/kernel/hpet.c > >> +++ b/arch/x86/kernel/hpet.c > >> @@ -930,8 +930,6 @@ int __init hpet_enable(void) > >> return 0; > >> > >> hpet_set_mapping(); > >> - if (!hpet_virt_address) > >> - return 0; > >> > >> /* Validate that the config register is working */ > >> if (!hpet_cfg_working()) > > > > FWIW, this patch looks harmless. It is checking for a failure in > > hpet_set_mapping(), and avoids the following code from performing > > 0-offset reads. hpet_set_mapping() is likely to never fail in real-world > > situations. *shrug* > > 'likely never to fail' is clearly a receipe for disaster and you should > know that. Of course -- I prefer to keep the sanity check. It just wasn't as good as it could have been: it's not clear just by looking at the patch how hpet_virt_address and hpet_set_mapping() are related. > > > I think it would make more sense for the check to live in > > hpet_cfg_working(), though. > > No. That does not make any sense at all. > > The proper change would have been to make hpet_set_mapping() return > an error/success code and act on that. > > But that does _NOT_ make the patch invalid. > > I'm pretty sure that I looked at it and thought about the proper > solution (see above) and then shrugged it off because of overload... Right, no, I was saying the original patch should stay. It shouldn't be reverted. Greg, please drop this patch from the revert list. -- Kees Cook