From: Daniel Gruss <daniel.gruss@iaik.tugraz.at> To: Mark Rutland <mark.rutland@arm.com> Cc: David Gens <david.gens@cs.tu-darmstadt.de>, Thomas Garnier <thgarnie@google.com>, kernel list <linux-kernel@vger.kernel.org>, "Kernel Hardening" <kernel-hardening@lists.openwall.com>, <clementine.maurice@iaik.tugraz.at>, <moritz.lipp@iaik.tugraz.at>, "Michael Schwarz" <michael.schwarz@iaik.tugraz.at>, Richard Fellner <richard.fellner@student.tugraz.at>, "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>, Ingo Molnar <mingo@kernel.org>, <anders.fogh@gdata-adan.de> Subject: Re: [kernel-hardening] [RFC, PATCH] x86_64: KAISER - do not map kernel in user mode Date: Mon, 8 May 2017 12:51:27 +0200 [thread overview] Message-ID: <db80ae9d-15bc-5d32-afce-ea98a6059fb8@iaik.tugraz.at> (raw) In-Reply-To: <20170508102100.GA5480@leverpostej> > While it may be the case that in practice ARM systems do not have such a > side channel, I think that it is erroneous to believe that the > architectural TTBR{0,1} split ensures this. > > The use of TTBR0 for user and TTBR1 for kernel is entirely a SW policy, > and not an architectural requirement. It is possible to map data in > TTBR1 which is accessible to userspace, and data in TTBR0 which is only > accessible by the kernel. In either case, this is determined by the page > tables themselves. Absolutely right, but TTBR0 and TTBR1 are usually used in this way. > Given this, I think that the statements in the KAISER paper regarding > the TTBRs (in section 2.1) are not quite right. Architecturally, > permission checks and lookups cannot be elided based on the TTBR used. As we say in section 2.1, they are "typically" used in this way, and this prevents the attacks. Not just the presence of a second register, but the way how the two registers are used to split the translation tables for user and kernel.
WARNING: multiple messages have this Message-ID (diff)
From: Daniel Gruss <daniel.gruss@iaik.tugraz.at> To: Mark Rutland <mark.rutland@arm.com> Cc: David Gens <david.gens@cs.tu-darmstadt.de>, Thomas Garnier <thgarnie@google.com>, kernel list <linux-kernel@vger.kernel.org>, Kernel Hardening <kernel-hardening@lists.openwall.com>, clementine.maurice@iaik.tugraz.at, moritz.lipp@iaik.tugraz.at, Michael Schwarz <michael.schwarz@iaik.tugraz.at>, Richard Fellner <richard.fellner@student.tugraz.at>, "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>, Ingo Molnar <mingo@kernel.org>, anders.fogh@gdata-adan.de Subject: Re: [kernel-hardening] [RFC, PATCH] x86_64: KAISER - do not map kernel in user mode Date: Mon, 8 May 2017 12:51:27 +0200 [thread overview] Message-ID: <db80ae9d-15bc-5d32-afce-ea98a6059fb8@iaik.tugraz.at> (raw) In-Reply-To: <20170508102100.GA5480@leverpostej> > While it may be the case that in practice ARM systems do not have such a > side channel, I think that it is erroneous to believe that the > architectural TTBR{0,1} split ensures this. > > The use of TTBR0 for user and TTBR1 for kernel is entirely a SW policy, > and not an architectural requirement. It is possible to map data in > TTBR1 which is accessible to userspace, and data in TTBR0 which is only > accessible by the kernel. In either case, this is determined by the page > tables themselves. Absolutely right, but TTBR0 and TTBR1 are usually used in this way. > Given this, I think that the statements in the KAISER paper regarding > the TTBRs (in section 2.1) are not quite right. Architecturally, > permission checks and lookups cannot be elided based on the TTBR used. As we say in section 2.1, they are "typically" used in this way, and this prevents the attacks. Not just the presence of a second register, but the way how the two registers are used to split the translation tables for user and kernel.
next prev parent reply other threads:[~2017-05-08 10:52 UTC|newest] Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top 2017-05-04 10:02 [RFC, PATCH] x86_64: KAISER - do not map kernel in user mode Daniel Gruss 2017-05-04 10:02 ` [kernel-hardening] " Daniel Gruss 2017-05-04 12:26 ` Daniel Gruss 2017-05-04 12:26 ` [kernel-hardening] " Daniel Gruss 2017-05-04 15:28 ` [kernel-hardening] " Thomas Garnier 2017-05-04 15:28 ` Thomas Garnier 2017-05-05 8:23 ` Daniel Gruss 2017-05-05 8:23 ` Daniel Gruss 2017-05-05 15:47 ` Thomas Garnier 2017-05-05 15:47 ` Thomas Garnier 2017-05-06 4:02 ` David Gens 2017-05-06 8:38 ` Daniel Gruss 2017-05-06 8:38 ` Daniel Gruss 2017-05-08 10:21 ` Mark Rutland 2017-05-08 10:51 ` Daniel Gruss [this message] 2017-05-08 10:51 ` Daniel Gruss 2017-05-08 13:22 ` Mark Rutland 2017-05-08 13:43 ` Daniel Gruss 2017-05-08 13:43 ` Daniel Gruss 2017-05-08 13:53 ` Daniel Gruss 2017-05-08 13:53 ` Daniel Gruss 2017-05-08 14:09 ` Thomas Garnier 2017-05-08 14:19 ` Daniel Gruss 2017-05-08 14:19 ` Daniel Gruss 2017-05-08 13:23 ` Daniel Gruss 2017-05-08 13:23 ` Daniel Gruss 2017-05-04 15:47 ` Christoph Hellwig 2017-05-04 15:47 ` [kernel-hardening] " Christoph Hellwig 2017-05-05 7:40 ` Daniel Gruss 2017-05-05 7:40 ` [kernel-hardening] " Daniel Gruss 2017-05-07 20:20 ` Richard Weinberger 2017-05-07 20:20 ` Richard Weinberger 2017-05-07 21:45 ` Daniel Gruss 2017-05-07 21:45 ` Daniel Gruss 2017-05-07 22:02 ` Richard Weinberger 2017-05-07 22:02 ` Richard Weinberger 2017-05-07 22:18 ` Daniel Gruss 2017-05-07 22:18 ` Daniel Gruss 2017-05-09 14:44 ` [kernel-hardening] Re: [RFC, PATCH] x86_64: KAISER - do not mapkernel " Fogh, Anders 2017-05-09 14:44 ` Fogh, Anders 2017-05-09 14:57 ` Richard Weinberger 2017-05-09 14:57 ` Richard Weinberger 2017-05-09 15:30 ` Rik van Riel 2017-05-09 15:30 ` Rik van Riel 2017-10-31 23:28 ` Dave Hansen 2017-10-31 23:28 ` Dave Hansen 2017-05-05 15:49 ` [kernel-hardening] [RFC, PATCH] x86_64: KAISER - do not map kernel " Jann Horn 2017-05-05 15:49 ` Jann Horn 2017-05-05 15:53 ` Jann Horn 2017-05-05 15:53 ` Jann Horn 2017-05-06 8:28 ` Daniel Gruss 2017-05-06 8:28 ` Daniel Gruss
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