From: Catalin Marinas <catalin.marinas@arm.com>
To: "Pierre-Clément Tosi" <ptosi@google.com>
Cc: Will Deacon <will@kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
Vincenzo Frascino <vincenzo.frascino@arm.com>,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org,
Peter Collingbourne <peter@pcc.me.uk>,
stable@vger.kernel.org
Subject: Re: [PATCH 01/24] arm64: Fix lazy TCO clear when enabling user MTE
Date: Tue, 10 Nov 2026 18:33:20 +0000 [thread overview]
Message-ID: <avNjcKtuQkZW0_Sr@arm.com> (raw)
In-Reply-To: <20261107-mte-kasan-split-v1-1-d84ea5f30f94@google.com>
On Sat, Nov 07, 2026 at 04:36:07PM +0100, Pierre-Clément Tosi wrote:
> On kernel entry from EL0 with HW KASAN inactive and user MTE disabled or
> in async mode, mte_disable_tco_entry() leaves PSTATE.TCO set to avoid an
> expensive write, as it assumes that EL1 tag checks are not needed.
>
> However, if the thread is in the process of enabling sync or asymm MTE,
> set_mte_ctrl() updates SCTLR_EL1.TCF0 without clearing PSTATE.TCO! As a
> result, kernel uaccesses miss tag faults until the next context switch.
Nit: next context switch or another syscall. I think this makes it
clearer that the only potential missed tag accesses after the prctl() is
a signal frame write as we don't have other uaccesses.
> Clear TCO in set_mte_ctrl() immediately after setting the task's SCTLR.
>
> Cc: Peter Collingbourne <peter@pcc.me.uk>
> Cc: stable@vger.kernel.org
> Fixes: 38ddf7dafaea ("arm64: mte: avoid clearing PSTATE.TCO on entry unless necessary")
> Signed-off-by: Pierre-Clément Tosi <ptosi@google.com>
The patch is correct but I wonder whether we need a cc stable.
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
next prev parent reply other threads:[~2026-11-10 18:33 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-11-07 15:36 [PATCH 00/24] arm64: Decouple MTE code from KASAN support Pierre-Clément Tosi
2026-11-07 15:36 ` [PATCH 01/24] arm64: Fix lazy TCO clear when enabling user MTE Pierre-Clément Tosi
2026-11-10 18:33 ` Catalin Marinas [this message]
2026-11-07 15:36 ` [PATCH 02/24] kselftest/arm64: Test lazy PSTATE.TCO handling Pierre-Clément Tosi
2026-11-07 15:36 ` [PATCH 03/24] arm64: Fix volatility of IRG inline assembly Pierre-Clément Tosi
2026-11-07 15:36 ` [PATCH 04/24] arm64: Skip TCO on privileged uaccess without kMTE Pierre-Clément Tosi
2026-11-07 15:36 ` [PATCH 05/24] arm64: Check MTE once per fault-handling section Pierre-Clément Tosi
2026-11-07 15:36 ` [PATCH 06/24] arm64: Harden is_ttbr1_addr() on tagged addresses Pierre-Clément Tosi
2026-11-07 15:36 ` [PATCH 07/24] arm64: Skip redundant TCO clear post-kernel entry Pierre-Clément Tosi
2026-11-07 15:36 ` [PATCH 08/24] arm64: Introduce mte_get_reset_tfsr() helpers Pierre-Clément Tosi
2026-11-07 15:36 ` [PATCH 09/24] kasan: rework hw_{force=>flush}_async_tag_fault() Pierre-Clément Tosi
2026-11-07 15:36 ` [PATCH 10/24] kasan: rework hw_{get=>set}_random_tag() Pierre-Clément Tosi
2026-11-07 15:36 ` [PATCH 11/24] kasan: provide empty stub for kasan_report_async() Pierre-Clément Tosi
2026-11-07 15:36 ` [PATCH 12/24] kasan: drop mte-kasan.h from arch-agnostic header Pierre-Clément Tosi
2026-11-07 15:36 ` [PATCH 13/24] arm64: Introduce set_pstate_tco() helper macro Pierre-Clément Tosi
2026-11-07 15:36 ` [PATCH 14/24] arm64: Add mte_{enter,exit}_*_{kernel,user}_mode() Pierre-Clément Tosi
2026-11-07 15:36 ` [PATCH 15/24] arm64: Refactor and remove mte_disable_tco_entry() Pierre-Clément Tosi
2026-11-07 15:36 ` [PATCH 16/24] arm64: Refactor KERNEL_GCR_EL1 out of <sysreg.h> Pierre-Clément Tosi
2026-11-07 15:36 ` [PATCH 17/24] arm64: Introduce MTE & KASAN tag handling helpers Pierre-Clément Tosi
2026-11-07 15:36 ` [PATCH 18/24] arm64: Inline and remove mte_check_tfsr_*() Pierre-Clément Tosi
2026-11-07 15:36 ` [PATCH 19/24] arm64: Rework static branches for kernel MTE Pierre-Clément Tosi
2026-11-07 15:36 ` [PATCH 20/24] arm64: Move MTE insn wrappers to <asm/mte-def.h> Pierre-Clément Tosi
2026-11-07 15:36 ` [PATCH 21/24] arm64: Introduce mte_tag[_and_zero]_range() Pierre-Clément Tosi
2026-11-07 15:36 ` [PATCH 22/24] arm64: Consolidate MTE-based KASAN in mte-kasan.h Pierre-Clément Tosi
2026-11-07 15:36 ` [PATCH 23/24] arm64: Fold <asm/mte-kasan.h> into <asm/kasan.h> Pierre-Clément Tosi
2026-11-07 15:36 ` [PATCH 24/24] arm64: Introduce CONFIG_ARM64_MTE_KERNEL Pierre-Clément Tosi
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