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[95.114.116.215]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-47f96d4656bsm27341954f8f.21.2026.07.26.18.28.41 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 26 Jul 2026 18:28:41 -0700 (PDT) Date: Mon, 27 Jul 2026 03:28:09 +0200 From: Karl Mehltretter To: Kees Cook Cc: "Russell King (Oracle)" , Linus Walleij , Nathan Chancellor , Sami Tolvanen , Zhen Lei , Arnd Bergmann , =?utf-8?Q?Micha=C5=82?= Pecio , Sebastian Andrzej Siewior , linux-arm-kernel@lists.infradead.org, Russell King , Will Deacon , Mark Rutland , Nick Desaulniers , Bill Wendling , Justin Stitt , 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 Message-ID: References: <20260715175223.make.153-kees@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260715175223.make.153-kees@kernel.org> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260726_182845_432089_DE1B3FCA X-CRM114-Status: GOOD ( 12.38 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Wed, Jul 15, 2026 at 10:52:27AM +0100, Kees Cook wrote: > +/* UDF base pattern with KCFI bit: cond=0xe, 0x7f, xxxx, 1xxx, 0xf, xxxx */ > +#define CFI_UDF_IMM_BASE 0xe7f008f0 > +#define CFI_UDF_IMM_MASK 0xfff008f0 /* Mask for UDF + KCFI bit matching */ With this patch applied, KGDB and CONFIG_CFI cannot be used together. Setting a breakpoint causes Oops as CFI failure. This patch on top of "ARM: breakpoint: CFI breakpoints only on demand", multi_v7_defconfig + CONFIG_CFI=y + KGDB/KGDB_KDB/MAGIC_SYSRQ, THUMB2_KERNEL=n, clang 22.1.8 LLVM=1, qemu-system-arm -M virt -cpu cortex-a15, booted with kgdboc=ttyAMA0. Then "echo g > /proc/sysrq-trigger": sysrq: DEBUG CFI failure at kgdb_breakpoint+0x2c/0x58 (target: kgdb_breakpoint+0x2c/0x58; expected type: 0xc0472d70) Internal error: Oops - CFI: 0 [#1] SMP ARM Modules linked in: CPU: 0 UID: 0 PID: 1 Comm: init Not tainted 7.2.0-rc3-00278-g38436106b2f5-dirty #1 VOLUNTARY Hardware name: Generic DT based system PC is at kgdb_breakpoint+0x2c/0x58 LR is at kgdb_breakpoint+0x2c/0x58 pc : [] lr : [] psr: 60000013 sp : e080dea8 ip : 00000000 fp : 0021a1c0 r10: 00000000 r9 : 00000000 r8 : c2004048 r7 : c2205d9c r6 : 00000000 r5 : c1609558 r4 : c22bb994 r3 : 00000000 r2 : 00000000 r1 : 00000000 r0 : 00000000 Flags: nZCv IRQs on FIQs on Mode SVC_32 ISA ARM Segment none ... kgdb_breakpoint from __handle_sysrq+0x150/0x158 Thanks, Karl