From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 727691E25E1; Wed, 19 Feb 2025 08:53:33 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739955213; cv=none; b=M2gX9NAt7yW6MPULQF0vcKClSQnpxSbV+kZ9C3+nxlhxzQzAhe8NAmKI28S14OSUVaDrtF2vNTpOq6GGbxe7m5wAoNKgI66pqR8xxNpMFoLNIlMZI0qlHITbt9+1FfFCfDFj1zxKw7AjjZpZSb0bO47Fr8ZkV3YzU8a4CnikMq4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739955213; c=relaxed/simple; bh=H7olvc8Uc2awvIC+E7bLsOniZDDLx0DX4Rm0vDTQMVM=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=BJF5xMivWNr+0SZOe0W+7uruJYVBU+B0poEqpr2KOcUphHRq9B6ahcInGetJMHqNpE4reqKjEyYXLAjWAz206xDruhhA6aXTkGOh92WGlazkirnLJJ/9im3qBCxn8qJOcnvzIa9EBl3Xi1IWA6aD8NaXp/mPhFTZoLS7ImhmUiI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=vVctD9M0; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="vVctD9M0" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8C1E1C4CEE8; Wed, 19 Feb 2025 08:53:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1739955213; bh=H7olvc8Uc2awvIC+E7bLsOniZDDLx0DX4Rm0vDTQMVM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=vVctD9M0c6+Ruzn64b5uTAozXKPLtI0zd96qJrPLa77M7y1/yf/ADbt0eaINV9fMU bCSfv4M8NZu8fqS5+rEQ9toirqy9rsKc6CLo2Lz5p5cd7C9PgcsCZtzAMYlO+xY7Ko w1NfbskqN87K7DBAy7RTuEqL8wWdL96Tft1qedq4= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, "Maciej W. Rozycki" , Magnus Lindholm , Matt Turner , Ivan Kokshaysky Subject: [PATCH 6.12 134/230] alpha: make stack 16-byte aligned (most cases) Date: Wed, 19 Feb 2025 09:27:31 +0100 Message-ID: <20250219082606.927583939@linuxfoundation.org> X-Mailer: git-send-email 2.48.1 In-Reply-To: <20250219082601.683263930@linuxfoundation.org> References: <20250219082601.683263930@linuxfoundation.org> User-Agent: quilt/0.68 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.12-stable review patch. If anyone has any objections, please let me know. ------------------ From: Ivan Kokshaysky commit 0a0f7362b0367634a2d5cb7c96226afc116f19c9 upstream. The problem is that GCC expects 16-byte alignment of the incoming stack since early 2004, as Maciej found out [1]: Having actually dug speculatively I can see that the psABI was changed in GCC 3.5 with commit e5e10fb4a350 ("re PR target/14539 (128-bit long double improperly aligned)") back in Mar 2004, when the stack pointer alignment was increased from 8 bytes to 16 bytes, and arch/alpha/kernel/entry.S has various suspicious stack pointer adjustments, starting with SP_OFF which is not a whole multiple of 16. Also, as Magnus noted, "ALPHA Calling Standard" [2] required the same: D.3.1 Stack Alignment This standard requires that stacks be octaword aligned at the time a new procedure is invoked. However: - the "normal" kernel stack is always misaligned by 8 bytes, thanks to the odd number of 64-bit words in 'struct pt_regs', which is the very first thing pushed onto the kernel thread stack; - syscall, fault, interrupt etc. handlers may, or may not, receive aligned stack depending on numerous factors. Somehow we got away with it until recently, when we ended up with a stack corruption in kernel/smp.c:smp_call_function_single() due to its use of 32-byte aligned local data and the compiler doing clever things allocating it on the stack. This adds padding between the PAL-saved and kernel-saved registers so that 'struct pt_regs' have an even number of 64-bit words. This makes the stack properly aligned for most of the kernel code, except two handlers which need special threatment. Note: struct pt_regs doesn't belong in uapi/asm; this should be fixed, but let's put this off until later. Link: https://lore.kernel.org/rcu/alpine.DEB.2.21.2501130248010.18889@angie.orcam.me.uk/ [1] Link: https://bitsavers.org/pdf/dec/alpha/Alpha_Calling_Standard_Rev_2.0_19900427.pdf [2] Cc: stable@vger.kernel.org Tested-by: Maciej W. Rozycki Tested-by: Magnus Lindholm Tested-by: Matt Turner Reviewed-by: Maciej W. Rozycki Signed-off-by: Ivan Kokshaysky Signed-off-by: Matt Turner Signed-off-by: Greg Kroah-Hartman --- arch/alpha/include/uapi/asm/ptrace.h | 2 ++ 1 file changed, 2 insertions(+) --- a/arch/alpha/include/uapi/asm/ptrace.h +++ b/arch/alpha/include/uapi/asm/ptrace.h @@ -42,6 +42,8 @@ struct pt_regs { unsigned long trap_a0; unsigned long trap_a1; unsigned long trap_a2; +/* This makes the stack 16-byte aligned as GCC expects */ + unsigned long __pad0; /* These are saved by PAL-code: */ unsigned long ps; unsigned long pc;