From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from ozlabs.org (bilbo.ozlabs.org [IPv6:2401:3900:2:1::2]) (using TLSv1.2 with cipher ADH-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 42LQFk2NrHzF33Q for ; Thu, 27 Sep 2018 16:41:46 +1000 (AEST) From: Michael Ellerman To: Michael Neuling Cc: linuxppc-dev@lists.ozlabs.org, Nicholas Piggin , paulus@ozlabs.org, benh@kernel.crashing.org, Breno Leitao , aneesh.kumar@linux.vnet.ibm.com Subject: Re: [PATCH] powerpc/tm: Avoid possible userspace r1 corruption on reclaim In-Reply-To: References: <20180925093647.23723-1-mikey@neuling.org> <87d0t14wiz.fsf@concordia.ellerman.id.au> Date: Thu, 27 Sep 2018 16:41:45 +1000 Message-ID: <87d0szv3va.fsf@concordia.ellerman.id.au> MIME-Version: 1.0 Content-Type: text/plain List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Michael Neuling writes: > On Tue, 2018-09-25 at 22:00 +1000, Michael Ellerman wrote: >> Michael Neuling writes: >> > Current we store the userspace r1 to PACATMSCRATCH before finally >> > saving it to the thread struct. >> > >> > In theory an exception could be taken here (like a machine check or >> > SLB miss) that could write PACATMSCRATCH and hence corrupt the >> > userspace r1. The SLB fault currently doesn't touch PACATMSCRATCH, but >> > others do. >> > >> > We've never actually seen this happen but it's theoretically >> > possible. Either way, the code is fragile as it is. >> > >> > This patch saves r1 to the kernel stack (which can't fault) before we >> > turn MSR[RI] back on. PACATMSCRATCH is still used but only with >> > MSR[RI] off. We then copy r1 from the kernel stack to the thread >> > struct once we have MSR[RI] back on. >> > >> > Suggested-by: Breno Leitao >> > Signed-off-by: Michael Neuling >> > --- >> > arch/powerpc/kernel/tm.S | 8 +++++++- >> > 1 file changed, 7 insertions(+), 1 deletion(-) >> > >> > diff --git a/arch/powerpc/kernel/tm.S b/arch/powerpc/kernel/tm.S >> > index 701b0f5b09..8207816a1e 100644 >> > --- a/arch/powerpc/kernel/tm.S >> > +++ b/arch/powerpc/kernel/tm.S >> > @@ -178,6 +178,12 @@ _GLOBAL(tm_reclaim) >> > >> > std r11, GPR11(r1) /* Temporary stash */ >> > >> > + /* Move r1 to kernel stack in case PACATMSCRATCH is used once >> > + * we turn on RI >> > + */ >> >> I see we still need to send you to Comment Formatting Re-Education Camp. > > The rest of that file has they style, so I'm just keeping with that. I can > submit a patch later to fix them all up. Sure, but let's not add new ones. And yeah fixing them all up in another patch would be good. cheers