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From: Karl Mehltretter <kmehltretter@gmail.com>
To: Kees Cook <kees@kernel.org>
Cc: "Russell King (Oracle)" <rmk+kernel@armlinux.org.uk>,
	"Linus Walleij" <linusw@kernel.org>,
	"Nathan Chancellor" <nathan@kernel.org>,
	"Sami Tolvanen" <samitolvanen@google.com>,
	"Zhen Lei" <thunder.leizhen@huawei.com>,
	"Arnd Bergmann" <arnd@arndb.de>,
	"Michał Pecio" <michal.pecio@gmail.com>,
	"Sebastian Andrzej Siewior" <bigeasy@linutronix.de>,
	linux-arm-kernel@lists.infradead.org,
	"Russell King" <linux@armlinux.org.uk>,
	"Will Deacon" <will@kernel.org>,
	"Mark Rutland" <mark.rutland@arm.com>,
	"Nick Desaulniers" <ndesaulniers@google.com>,
	"Bill Wendling" <morbo@google.com>,
	"Justin Stitt" <justinstitt@google.com>,
	linux-kernel@vger.kernel.org, llvm@lists.linux.dev,
	linux-hardening@vger.kernel.org
Subject: Re: [PATCH v3] ARM: traps: Implement KCFI trap handler for ARM32
Date: Mon, 27 Jul 2026 03:37:16 +0200	[thread overview]
Message-ID: <ama1UiT1Jxy-PvVN@gmail.com> (raw)
In-Reply-To: <20260715175223.make.153-kees@kernel.org>

On Wed, Jul 15, 2026 at 10:52:27AM +0100, Kees Cook wrote:
> +			/* Check for EOR/EORS immediate: cccc 0010 0x1n Rn Rd immediate */
> +			if ((instr_prev & 0x0fe00000) == 0x02200000) {
> +				/* Extract EOR immediate value and XOR to reconstruct type */
> +				u32 rotate = (instr_prev >> 8) & 0xf;
> +				u32 imm8 = instr_prev & 0xff;
> +				u32 imm32 = (imm8 >> (rotate * 2)) | (imm8 << (32 - rotate * 2));

With CONFIG_UBSAN_SHIFT=y, I reproduced the following in QEMU with GCC
v14 KCFI and LKDTM CFI_FORWARD_PROTO:

  UBSAN: shift-out-of-bounds in arch/arm/kernel/traps.c:555:48
  shift exponent 32 is too large for 32-bit type 'unsigned int'

Could this use ror32() from <linux/bitops.h> instead?

Thanks,
Karl

      parent reply	other threads:[~2026-07-27  1:37 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2026-07-15 17:52 [PATCH v3] ARM: traps: Implement KCFI trap handler for ARM32 Kees Cook
2026-07-21  0:11 ` Nathan Chancellor
2026-07-21  7:54 ` Linus Walleij
2026-07-21 16:15   ` Nick Desaulniers
2026-07-27  0:10 ` Karl Mehltretter
2026-07-27  1:28 ` Karl Mehltretter
2026-07-27  1:37 ` Karl Mehltretter [this message]

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