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From: Will Deacon <will@kernel.org>
To: Peter Collingbourne <pcc@google.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
	Kevin Brodsky <kevin.brodsky@arm.com>,
	Kostya Serebryany <kcc@google.com>,
	Evgenii Stepanov <eugenis@google.com>,
	Andrey Konovalov <andreyknvl@google.com>,
	Vincenzo Frascino <vincenzo.frascino@arm.com>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	Richard Henderson <rth@twiddle.net>
Subject: Re: [PATCH v3] arm64: Expose original FAR_EL1 value in sigcontext
Date: Wed, 29 Apr 2020 22:08:26 +0100	[thread overview]
Message-ID: <20200429210826.GA8604@willie-the-truck> (raw)
In-Reply-To: <20200327191915.257116-1-pcc@google.com>

On Fri, Mar 27, 2020 at 12:19:15PM -0700, Peter Collingbourne wrote:
> The kernel currently clears the tag bits (i.e. bits 56-63) in the fault
> address exposed via siginfo.si_addr and sigcontext.fault_address. However,
> the tag bits may be needed by tools in order to accurately diagnose
> memory errors, such as HWASan [1] or future tools based on the Memory
> Tagging Extension (MTE).
> 
> We should not stop clearing these bits in the existing fault address
> fields, because there may be existing userspace applications that are
> expecting the tag bits to be cleared. Instead, create a far_context in
> sigcontext (similar to the existing esr_context), and store the original
> value of FAR_EL1 (including the tag bits) there.
> 
> [1] http://clang.llvm.org/docs/HardwareAssistedAddressSanitizerDesign.html
> 
> Signed-off-by: Peter Collingbourne <pcc@google.com>
> ---
> v3:
> - add documentation to tagged-pointers.rst
> - update comments in sigcontext.h

Hmm, although the code looks fine, why don't we just expose the tag in the
new field, rather than duplicate the address information? I'm nervous about
exposing privileged registers directly to userspace.

Also, Catalin, could you elaborate on the MTE use-case please? The
architecture says that FAR_EL1[63:60] are UNKNOWN on a synchronous tag
check fault, so we'd have to *avoid* exposing them in that case!

Will

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  parent reply	other threads:[~2020-04-29 21:08 UTC|newest]

Thread overview: 63+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-12 17:17 [PATCH] arm64: Expose original FAR_EL1 value in sigcontext Peter Collingbourne
2020-03-25 13:10 ` Catalin Marinas
2020-03-25 17:41   ` Peter Collingbourne
2020-03-25 17:40 ` [PATCH v2] " Peter Collingbourne
2020-03-26 16:45   ` Catalin Marinas
2020-03-27  7:56     ` Will Deacon
2020-03-27 11:39       ` Catalin Marinas
2020-03-27 19:26         ` Peter Collingbourne
2020-03-27 19:19   ` [PATCH v3] " Peter Collingbourne
2020-04-22 14:25     ` Catalin Marinas
2020-04-29 21:08     ` Will Deacon [this message]
2020-04-29 21:42       ` Peter Collingbourne
2020-05-04 17:03         ` Will Deacon
2020-05-07 17:57           ` [PATCH v4] arm64: Expose FAR_EL1 tag bits " Peter Collingbourne
2020-05-08  2:01             ` [PATCH v5] " Peter Collingbourne
2020-05-12 16:25               ` Catalin Marinas
2020-05-13 18:09               ` [PATCH v6] " Peter Collingbourne
2020-05-13 20:28                 ` Dave Martin
2020-05-15  0:58                   ` Peter Collingbourne
2020-05-18  9:53                     ` Dave Martin
2020-05-19 22:00                       ` Peter Collingbourne
2020-05-20  8:55                         ` Will Deacon
2020-05-20  9:26                           ` Dave Martin
2020-05-21  2:28                             ` Peter Collingbourne
2020-05-21  2:29                               ` [PATCH v6 0/3] " Peter Collingbourne
2020-05-21  2:29                                 ` [PATCH v6 1/3] signal: Allow architectures to store arch-specific data in kernel_siginfo Peter Collingbourne
2020-05-21  2:29                                 ` [PATCH v6 2/3] arm64: Move fault address and fault code into kernel_siginfo Peter Collingbourne
2020-05-21 13:34                                   ` kbuild test robot
2020-05-21  2:29                                 ` [PATCH v6 3/3] arm64: Expose FAR_EL1 tag bits in sigcontext Peter Collingbourne
2020-05-21 12:35                               ` [PATCH v6] " Eric W. Biederman
2020-05-21 18:03                                 ` Peter Collingbourne
2020-05-21 19:24                                   ` Eric W. Biederman
2020-05-21 20:48                                     ` Peter Collingbourne
2020-06-08 18:12                                       ` Peter Collingbourne
2020-06-08 18:14                                         ` [PATCH v7] arm64: Expose FAR_EL1 tag bits in siginfo Peter Collingbourne
     [not found]                                           ` <20200623020134.16655-1-pcc@google.com>
     [not found]                                             ` <87sgemrlgc.fsf@x220.int.ebiederm.org>
2020-06-23 14:38                                               ` [PATCH v8] " Dave Martin
2020-06-23 17:47                                                 ` Eric W. Biederman
2020-06-24  0:40                                                   ` Peter Collingbourne
2020-06-24  9:28                                                     ` Dave Martin
2020-06-24 16:51                                                       ` Peter Collingbourne
2020-06-24 17:12                                                         ` Dave Martin
2020-06-24 19:51                                                           ` Peter Collingbourne
2020-07-06 16:41                                                             ` Dave Martin
2020-07-06 19:20                                                               ` Peter Collingbourne
2020-07-07 14:19                                                                 ` Dave Martin
2020-07-07 19:07                                                                   ` Peter Collingbourne
2020-07-08 11:00                                                                     ` Dave Martin
2020-07-08 13:58                                                                       ` Dave Martin
2020-07-08 22:21                                                                         ` Peter Collingbourne
2020-07-13 13:24                                                                           ` Dave Martin
2020-07-13 20:50                                                                             ` Peter Collingbourne
2020-07-14 17:36                                                                               ` Dave Martin
2020-08-18  3:16                                                                                 ` Peter Collingbourne
2020-08-18 13:50                                                                                   ` Dave Martin
2020-06-23 14:57                                             ` Dave Martin
2020-05-26 13:03                                     ` [PATCH v6] arm64: Expose FAR_EL1 tag bits in sigcontext Dave Martin
2020-04-30  9:50       ` [PATCH v3] arm64: Expose original FAR_EL1 value " Catalin Marinas
2020-04-30  9:59         ` Will Deacon
2020-04-30 13:34           ` Catalin Marinas
2020-05-04 10:19     ` Dave Martin
2020-05-07 17:55       ` Peter Collingbourne
2020-05-13 17:27         ` Dave Martin
2020-05-13 18:00           ` Peter Collingbourne

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