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Date: Mon, 26 Mar 2018 17:43:42 +0000
From: Andy Lutomirski <luto@...nel.org>
To: Kees Cook <keescook@...omium.org>
Cc: Alexander Popov <alex.popov@...ux.com>, Dave Hansen <dave.hansen@...ux.intel.com>,
Peter Zijlstra <peterz@...radead.org>, Laura Abbott <labbott@...hat.com>,
Linus Torvalds <torvalds@...ux-foundation.org>, Andy Lutomirski <luto@...nel.org>,
PaX Team <pageexec@...email.hu>, Brad Spengler <spender@...ecurity.net>,
Ingo Molnar <mingo@...nel.org>, Tycho Andersen <tycho@...ho.ws>, Mark Rutland <mark.rutland@....com>,
Ard Biesheuvel <ard.biesheuvel@...aro.org>, Borislav Petkov <bp@...en8.de>,
Richard Sandiford <richard.sandiford@....com>, Thomas Gleixner <tglx@...utronix.de>,
"H . Peter Anvin" <hpa@...or.com>, "Dmitry V . Levin" <ldv@...linux.org>, Emese Revfy <re.emese@...il.com>,
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LKML <linux-kernel@...r.kernel.org>,
"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>
Subject: Re: [PATCH RFC v9 2/7] x86/entry: Add STACKLEAK erasing the kernel
stack at the end of syscalls
On Mon, Mar 26, 2018 at 5:32 PM, Kees Cook <keescook@...omium.org> wrote:
> On Thu, Mar 22, 2018 at 1:56 PM, Alexander Popov <alex.popov@...ux.com> wrote:
>> By the way, during my work on STACKLEAK, I've found one case when we get to the
>> userspace directly from the thread stack. Please see sysret32_from_system_call
>> in entry_64_compat.S. I checked that.
>>
>> IMO it seems odd, can the adversary use that to bypass PTI?
>
> If it was missing the page table swap, shouldn't this mean that the
> missing NX bit would immediately crash userspace?
sysret32_from_system_call does;
SWITCH_TO_USER_CR3_NOSTACK scratch_reg=%r8 scratch_reg2=%r9
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