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[2a02:3100:ada3:3901:ad33:2cf3:cf37:617f]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-49044775266sm22135525e9.33.2026.05.22.14.15.15 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Fri, 22 May 2026 14:15:16 -0700 (PDT) From: Karl Mehltretter To: Russell King Cc: Linus Walleij , "Russell King (Oracle)" , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, Karl Mehltretter Subject: [PATCH] ARM: entry: use byte load for KASAN VMAP stack shadow Date: Fri, 22 May 2026 23:15:03 +0200 Message-Id: <20260522211503.25219-1-kmehltretter@gmail.com> X-Mailer: git-send-email 2.39.5 (Apple Git-154) MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260522_141520_310593_EC1BC25B X-CRM114-Status: GOOD ( 12.77 ) 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 Commit 44e9a3bb76e5 ("ARM: 9430/1: entry: Do a dummy read from VMAP shadow") added a dummy read from the KASAN VMAP stack shadow in __switch_to(). The read uses ldr, but KASAN shadow memory is byte-granular and the computed shadow address is not guaranteed to be word aligned. Booting the QEMU versatilepb machine with an ARM926EJ-S CPU and CONFIG_KASAN=y, CONFIG_KASAN_VMALLOC=y and CONFIG_VMAP_STACK=y faults before init: Unhandled fault: alignment exception (0x001) at 0xb91037f6 PC is at __switch_to+0x64/0x88 Use ldrb for the dummy shadow access. The code only needs to fault if the shadow mapping is missing, so a byte load is sufficient and matches the granularity of KASAN shadow memory. Fixes: 44e9a3bb76e5 ("ARM: 9430/1: entry: Do a dummy read from VMAP shadow") Cc: stable@vger.kernel.org # v6.13+ Assisted-by: Codex:gpt-5 Signed-off-by: Karl Mehltretter --- arch/arm/kernel/entry-armv.S | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S index ef6a657c8d13..a3d050ce9b79 100644 --- a/arch/arm/kernel/entry-armv.S +++ b/arch/arm/kernel/entry-armv.S @@ -567,7 +567,7 @@ ENTRY(__switch_to) @ are using KASAN mov_l r2, KASAN_SHADOW_OFFSET add r2, r2, ip, lsr #KASAN_SHADOW_SCALE_SHIFT - ldr r2, [r2] + ldrb r2, [r2] #endif #endif -- 2.39.5 (Apple Git-154)