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Message-ID: <CALCETrXFO3Y5iVxn_J0-8h=sEU9TFbBk6F3J7dRXu+b0HsBE=A@mail.gmail.com> Date: Thu, 1 May 2014 14:39:20 -0700 From: Andy Lutomirski <luto@...capital.net> To: Andi Kleen <andi@...stfloor.org> Cc: "H. Peter Anvin" <hpa@...or.com>, X86 ML <x86@...nel.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Andi Kleen <ak@...ux.intel.com> Subject: Re: [PATCH 4/7] x86: Add support for rd/wr fs/gs base On Thu, May 1, 2014 at 2:15 PM, Andi Kleen <andi@...stfloor.org> wrote: >> If usergs == kernelgs, then ebx will always be 1 and we'll never end >> up in paranoid_userspace. > > You may miss a reschedule in this obscure case. It shouldn't really > happen because loading a kernel pointer is not useful for user space. > > Doesn't seem like a real issue to me. > > We only happen need to handle it to avoid crashing. Allowing userspace to prevent itself from being rescheduled by loading something strange into gsbase seems unfortunate. --Andy > >> Alternatively, what if the paranoid entry checked whether we're coming >> from userspace at the very beginning and, if so, just jumped to the >> non-paranoid entry? > > That would work, but I doubt it would be worth it. > > -Andi -- Andy Lutomirski AMA Capital Management, LLC -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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