From: Peter Zijlstra <peterz@infradead.org>
To: Andy Lutomirski <luto@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>,
Borislav Petkov <bp@alien8.de>, Laura Abbott <labbott@redhat.com>,
X86 ML <x86@kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
stable <stable@vger.kernel.org>
Subject: Re: Yet another KPTI regression with 4.14.x series in a VM
Date: Sat, 13 Jan 2018 13:08:47 +0100 [thread overview]
Message-ID: <20180113120847.GI3397@worktop> (raw)
In-Reply-To: <CALCETrWOpg_OXThyMC66JQu7JF=TxzRwFrEgunUZt3H+VUfxrQ@mail.gmail.com>
On Fri, Jan 12, 2018 at 10:08:20PM -0800, Andy Lutomirski wrote:
> Now this is quite a strange value to write to CR3. The 0x800 part
> means that we're using the "user" variant of the address space that
> would have ASID=0 and the 0x1000 bit being set corresponds to the user
> pgdir, but this is nonsense, since the kernel never uses PCID 0 for
> user mode. We always start at 1. The only exception is if
> X86_FEATURE_PCID is off. But, if X86_FEATURE_PCID is off, then we
> shouldn't be setting any PCID bits.
My bad, I was under the impression the lower 12 bits would be ignored
without PCID :/
> .Lwrcr3_\@:
> /* Flip the PGD and ASID to the user version */
> orq $(PTI_SWITCH_MASK), \scratch_reg
> mov \scratch_reg, %cr3
> .Lend_\@:
>
> That's bogus. PTI_SWITCH_MASK is 0x1800, which has PCID = 0x800.
> This should probably use an alternative to select between 0x1000 and
> 0x800 depending on X86_FEATURE_PCID or just use an entirely different
> label for the !PCID case.
ALTERNATIVE "orq $(PTI_SWITCH_PGTABLE_MASK), \scratch_reg",
"orq $(PTI_SWITCH_MASK), \scratch_reg", X86_FEATURE_PCID
Is not wanting to compile though; probably that whole alternative vs
macro thing again :/
next prev parent reply other threads:[~2018-01-13 12:08 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-12 18:19 Yet another KPTI regression with 4.14.x series in a VM Laura Abbott
2018-01-12 18:51 ` Thomas Gleixner
2018-01-12 21:30 ` Laura Abbott
2018-01-12 21:51 ` Thomas Gleixner
2018-01-13 6:08 ` Andy Lutomirski
2018-01-13 6:33 ` Willy Tarreau
2018-01-13 20:01 ` Andy Lutomirski
2018-01-13 20:45 ` Thomas Gleixner
2018-01-13 20:52 ` Andy Lutomirski
2018-01-13 12:08 ` Peter Zijlstra [this message]
2018-01-13 12:30 ` David Woodhouse
2018-01-13 13:10 ` Peter Zijlstra
2018-01-13 13:39 ` David Woodhouse
2018-01-13 14:14 ` David Woodhouse
2018-01-13 12:50 ` Thomas Gleixner
2018-01-13 13:51 ` Borislav Petkov
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