From: Nathan Chancellor <nathan@kernel.org>
To: Linus Walleij <linusw@kernel.org>
Cc: Russell King <linux@armlinux.org.uk>,
Sami Tolvanen <samitolvanen@google.com>,
Kees Cook <kees@kernel.org>,
"Russell King (Oracle)" <rmk+kernel@armlinux.org.uk>,
linux-arm-kernel@lists.infradead.org, stable@vger.kernel.org,
slipher <slipher@protonmail.com>,
Mark Rutland <mark.rutland@arm.com>,
Will Deacon <will@kernel.org>,
linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v4] ARM: breakpoint: CFI breakpoints only on demand
Date: Wed, 8 Jul 2026 11:53:18 -0700 [thread overview]
Message-ID: <20260708185318.GA2718700@ax162> (raw)
In-Reply-To: <20260703-arm32-cfi-bug-v4-1-c26acb640a8f@kernel.org>
On Fri, Jul 03, 2026 at 02:25:27PM +0200, Linus Walleij wrote:
> This removes the stub hw_breakpoint_cfi_handler() from ARM, making
> it not steal breakpoint type 0x03 (ARM_ENTRY_CFI_BREAKPOINT) unless
> CFI is actively used in the kernel.
>
> When not instrumenting with CFI, or when a breakpoint is issued in
> userspace, we fall through to return 1 from hw_breakpoint_pending()
> "unhandled fault" so userspace can make use of this breakpoint.
>
> Tested with LKDTM and this command line:
> echo CFI_FORWARD_PROTO > /sys/kernel/debug/provoke-crash/DIRECT
> still works as expected.
>
> Fixes: c3f89986fde7 ("ARM: 9391/2: hw_breakpoint: Handle CFI breakpoints")
> Reported-by: slipher <slipher@protonmail.com>
> Suggested-by: Mark Rutland <mark.rutland@arm.com>
> Closes: https://lore.kernel.org/lkml/kJqktbpLphg_Pk5I5SPptgTLjl3E3eq5mN5UzCslyFj7Q1Irp-wDid4mj5eQVd2iZtRGXgeZd8goq195EkXdjyt864YMc8mVb2B9NGH91NQ=@protonmail.com/
> Signed-off-by: Linus Walleij <linusw@kernel.org>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Tested-by: Nathan Chancellor <nathan@kernel.org>
--
Cheers,
Nathan
next prev parent reply other threads:[~2026-07-08 18:53 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-07-03 12:25 [PATCH v4] ARM: breakpoint: CFI breakpoints only on demand Linus Walleij
2026-07-03 12:48 ` sashiko-bot
2026-07-08 10:07 ` slipher
2026-07-08 18:53 ` Nathan Chancellor [this message]
2026-07-15 16:21 ` Kees Cook
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