From: Szabolcs Nagy <szabolcs.nagy@arm.com>
To: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>,
linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org,
linux-arch@vger.kernel.org, Dave P Martin <Dave.Martin@arm.com>,
Vincenzo Frascino <vincenzo.frascino@arm.com>,
Kevin Brodsky <kevin.brodsky@arm.com>,
Andrey Konovalov <andreyknvl@google.com>,
Peter Collingbourne <pcc@google.com>,
Andrew Morton <akpm@linux-foundation.org>,
libc-alpha@sourceware.org
Subject: Re: [PATCH v9 29/29] arm64: mte: Add Memory Tagging Extension documentation
Date: Wed, 23 Sep 2020 10:10:08 +0100 [thread overview]
Message-ID: <20200923091008.GC16385@arm.com> (raw)
In-Reply-To: <20200922165529.GH15643@gaia>
The 09/22/2020 17:55, Catalin Marinas wrote:
> On Tue, Sep 22, 2020 at 04:52:49PM +0100, Szabolcs Nagy wrote:
> > if we add a kernel level opt-in mechanism for tag checks later (e.g.
> > elf marking) or if the settings are exclusively owned by early libc
> > code then i think the proposed abi is ok (this is our current
> > agreement and works as long as no late runtime change is needed to the
> > settings).
>
> In the Android case, run-time changes to the tag checking mode I think
> are expected (usually via signal handlers), though per-thread.
ok that works, but does not help allocators or
runtimes that don't own the signal handlers.
> > i'm now wondering about the default tag check mode: it may be better
> > to enable sync tag checks in the kernel. it's not clear to me what
> > would break with that. this is probably late to discuss now and libc
> > would need ways to override the default no matter what, but i'd like
> > to know if somebody sees problems or risks with unconditional sync tag
> > checks turned on (sorry i don't remember if we went through this
> > before). i assume it would have no effect on a process that never uses
> > PROT_MTE.
>
> I don't think it helps much. We already have a requirement that to be
> able to pass tagged pointers to kernel syscalls, the user needs a
> prctl(PR_TAGGED_ADDR_ENABLE) call (code already in mainline). Using
> PROT_MTE without tagged pointers won't be of much use. So if we are to
> set different tag check defaults, we should also enable the tagged addr
> ABI automatically.
>
> That said, I still have a preference for MTE and tagged addr ABI to be
> explicitly requested by the (human) user either via environment
> variables or marked in an ELF note as "safe with/using tags". Given the
> recent mremap() issue we caused in glibc, I'm worried that other things
> may break with enabling the tagged addr ABI everywhere.
>
> Another aspect is that sync mode by default in a distro where glibc is
> MTE-aware will lead to performance regressions. That's another case in
> favour of the user explicitly asking for tag checking.
ok this all makes sense to me.
>
> Anyway, I'm open to having a debate on changing the defaults.
>
> --
> Catalin
WARNING: multiple messages have this Message-ID (diff)
From: Szabolcs Nagy <szabolcs.nagy@arm.com>
To: Catalin Marinas <catalin.marinas@arm.com>
Cc: linux-arch@vger.kernel.org, libc-alpha@sourceware.org,
Peter Collingbourne <pcc@google.com>,
Andrey Konovalov <andreyknvl@google.com>,
Kevin Brodsky <kevin.brodsky@arm.com>,
linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>,
Vincenzo Frascino <vincenzo.frascino@arm.com>,
Will Deacon <will@kernel.org>,
Dave P Martin <Dave.Martin@arm.com>,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v9 29/29] arm64: mte: Add Memory Tagging Extension documentation
Date: Wed, 23 Sep 2020 10:10:08 +0100 [thread overview]
Message-ID: <20200923091008.GC16385@arm.com> (raw)
In-Reply-To: <20200922165529.GH15643@gaia>
The 09/22/2020 17:55, Catalin Marinas wrote:
> On Tue, Sep 22, 2020 at 04:52:49PM +0100, Szabolcs Nagy wrote:
> > if we add a kernel level opt-in mechanism for tag checks later (e.g.
> > elf marking) or if the settings are exclusively owned by early libc
> > code then i think the proposed abi is ok (this is our current
> > agreement and works as long as no late runtime change is needed to the
> > settings).
>
> In the Android case, run-time changes to the tag checking mode I think
> are expected (usually via signal handlers), though per-thread.
ok that works, but does not help allocators or
runtimes that don't own the signal handlers.
> > i'm now wondering about the default tag check mode: it may be better
> > to enable sync tag checks in the kernel. it's not clear to me what
> > would break with that. this is probably late to discuss now and libc
> > would need ways to override the default no matter what, but i'd like
> > to know if somebody sees problems or risks with unconditional sync tag
> > checks turned on (sorry i don't remember if we went through this
> > before). i assume it would have no effect on a process that never uses
> > PROT_MTE.
>
> I don't think it helps much. We already have a requirement that to be
> able to pass tagged pointers to kernel syscalls, the user needs a
> prctl(PR_TAGGED_ADDR_ENABLE) call (code already in mainline). Using
> PROT_MTE without tagged pointers won't be of much use. So if we are to
> set different tag check defaults, we should also enable the tagged addr
> ABI automatically.
>
> That said, I still have a preference for MTE and tagged addr ABI to be
> explicitly requested by the (human) user either via environment
> variables or marked in an ELF note as "safe with/using tags". Given the
> recent mremap() issue we caused in glibc, I'm worried that other things
> may break with enabling the tagged addr ABI everywhere.
>
> Another aspect is that sync mode by default in a distro where glibc is
> MTE-aware will lead to performance regressions. That's another case in
> favour of the user explicitly asking for tag checking.
ok this all makes sense to me.
>
> Anyway, I'm open to having a debate on changing the defaults.
>
> --
> Catalin
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next prev parent reply other threads:[~2020-09-23 9:10 UTC|newest]
Thread overview: 68+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-04 10:30 [PATCH v9 00/29] arm64: Memory Tagging Extension user-space support Catalin Marinas
2020-09-04 10:30 ` [PATCH v9 01/29] arm64: mte: system register definitions Catalin Marinas
2020-09-04 10:30 ` [PATCH v9 02/29] arm64: mte: Use Normal Tagged attributes for the linear map Catalin Marinas
2020-09-04 10:30 ` [PATCH v9 03/29] arm64: mte: CPU feature detection and initial sysreg configuration Catalin Marinas
2020-09-04 10:30 ` [PATCH v9 04/29] arm64: kvm: mte: Hide the MTE CPUID information from the guests Catalin Marinas
2020-09-04 10:46 ` Marc Zyngier
2020-09-04 10:46 ` Marc Zyngier
2020-09-04 10:30 ` [PATCH v9 05/29] arm64: mte: Add specific SIGSEGV codes Catalin Marinas
2020-09-04 10:30 ` [PATCH v9 06/29] arm64: mte: Handle synchronous and asynchronous tag check faults Catalin Marinas
2020-09-04 10:30 ` [PATCH v9 07/29] mm: Add PG_arch_2 page flag Catalin Marinas
2020-09-04 10:30 ` [PATCH v9 08/29] mm: Preserve the PG_arch_2 flag in __split_huge_page_tail() Catalin Marinas
2020-09-04 10:30 ` [PATCH v9 09/29] arm64: mte: Clear the tags when a page is mapped in user-space with PROT_MTE Catalin Marinas
2020-09-10 10:23 ` Steven Price
2020-09-10 10:23 ` Steven Price
2020-09-10 10:52 ` Catalin Marinas
2020-09-10 10:52 ` Catalin Marinas
2020-09-10 11:12 ` Steven Price
2020-09-10 11:12 ` Steven Price
2020-09-10 11:55 ` Catalin Marinas
2020-09-10 11:55 ` Catalin Marinas
2020-09-10 12:43 ` Steven Price
2020-09-10 12:43 ` Steven Price
2020-09-04 10:30 ` [PATCH v9 10/29] arm64: mte: Tags-aware copy_{user_,}highpage() implementations Catalin Marinas
2020-09-04 10:30 ` [PATCH v9 11/29] arm64: Avoid unnecessary clear_user_page() indirection Catalin Marinas
2020-09-04 10:30 ` [PATCH v9 12/29] arm64: mte: Tags-aware aware memcmp_pages() implementation Catalin Marinas
2020-09-04 10:30 ` [PATCH v9 13/29] mm: Introduce arch_calc_vm_flag_bits() Catalin Marinas
2020-09-04 10:30 ` [PATCH v9 14/29] arm64: mte: Add PROT_MTE support to mmap() and mprotect() Catalin Marinas
2020-09-04 10:30 ` [PATCH v9 15/29] mm: Introduce arch_validate_flags() Catalin Marinas
2020-09-04 10:30 ` [PATCH v9 16/29] arm64: mte: Validate the PROT_MTE request via arch_validate_flags() Catalin Marinas
2020-09-04 10:30 ` [PATCH v9 17/29] mm: Allow arm64 mmap(PROT_MTE) on RAM-based files Catalin Marinas
2020-09-04 10:30 ` [PATCH v9 18/29] arm64: mte: Allow user control of the tag check mode via prctl() Catalin Marinas
2020-09-04 10:30 ` [PATCH v9 19/29] arm64: mte: Allow user control of the generated random tags " Catalin Marinas
2020-09-04 10:30 ` [PATCH v9 20/29] arm64: mte: Restore the GCR_EL1 register after a suspend Catalin Marinas
2020-09-04 10:30 ` [PATCH v9 21/29] arm64: mte: Allow {set,get}_tagged_addr_ctrl() on non-current tasks Catalin Marinas
2020-09-04 10:30 ` [PATCH v9 22/29] arm64: mte: ptrace: Add PTRACE_{PEEK,POKE}MTETAGS support Catalin Marinas
2020-09-04 10:30 ` [PATCH v9 23/29] arm64: mte: ptrace: Add NT_ARM_TAGGED_ADDR_CTRL regset Catalin Marinas
2020-09-04 10:30 ` [PATCH v9 24/29] fs: Handle intra-page faults in copy_mount_options() Catalin Marinas
2020-09-04 10:30 ` [PATCH v9 25/29] mm: Add arch hooks for saving/restoring tags Catalin Marinas
2020-09-04 10:30 ` [PATCH v9 26/29] arm64: mte: Enable swap of tagged pages Catalin Marinas
2020-09-04 10:30 ` [PATCH v9 27/29] arm64: mte: Save tags when hibernating Catalin Marinas
2020-09-04 10:30 ` [PATCH v9 28/29] arm64: mte: Kconfig entry Catalin Marinas
2020-09-04 10:30 ` [PATCH v9 29/29] arm64: mte: Add Memory Tagging Extension documentation Catalin Marinas
2020-09-17 8:11 ` Will Deacon
2020-09-17 8:11 ` Will Deacon
2020-09-17 9:02 ` Catalin Marinas
2020-09-17 9:02 ` Catalin Marinas
2020-09-17 16:15 ` Dave Martin
2020-09-17 16:15 ` Dave Martin
2020-09-18 8:30 ` Will Deacon
2020-09-18 8:30 ` Will Deacon
2020-10-14 23:43 ` Peter Collingbourne
2020-10-14 23:43 ` Peter Collingbourne
2020-10-14 23:43 ` Peter Collingbourne
2020-10-15 8:57 ` Will Deacon
2020-10-15 8:57 ` Will Deacon
2020-10-15 11:14 ` Szabolcs Nagy
2020-10-15 11:14 ` Szabolcs Nagy
2020-09-22 16:04 ` Catalin Marinas
2020-09-22 16:04 ` Catalin Marinas
2020-09-22 15:52 ` Szabolcs Nagy
2020-09-22 15:52 ` Szabolcs Nagy
2020-09-22 16:55 ` Catalin Marinas
2020-09-22 16:55 ` Catalin Marinas
2020-09-23 9:10 ` Szabolcs Nagy [this message]
2020-09-23 9:10 ` Szabolcs Nagy
2020-09-22 12:22 ` Andrey Konovalov
2020-09-22 12:22 ` Andrey Konovalov
2020-09-22 12:22 ` Andrey Konovalov
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