From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 8D01633D8 for ; Thu, 19 Sep 2024 09:14:53 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1726737295; cv=none; b=OJCLXd9B6iaJjlG4ibswBhfhunqJUBpMAa/4KlTKZISuhWrZ1uYTnceKBViX0kbf7VgBjVTJ2b5WV/pFudicHnWd5L/S1bDjQ4TlRxxQCYbtkMDgSqW2bK18EK8nPRpHcVlHH7XU8YGqCbHtu6yjODsSUevaGUUilDZnSkUeeL8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1726737295; c=relaxed/simple; bh=/Bop51NWsFXZqPBpDi2uoPivsk+HiblKv2mVbioil0U=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=qgX+XA/+mjCW3Za5WU6TDgLOXM3yWmH3ZAzX86bhPrT9+cBc+IYXT/QMmq9N2rk28z46STA/KU0QT7TrsY5dM/NrJPt0yWYW4AAALmu8DMM0A3gbnOXVR/ps0iVLVlu4VO7SD0O3m6Y8ZaxELFM+ROmRGCMzkgMJjfpCks23hlQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 4F0451007; Thu, 19 Sep 2024 02:15:22 -0700 (PDT) Received: from J2N7QTR9R3 (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 9EF2B3F71A; Thu, 19 Sep 2024 02:14:50 -0700 (PDT) Date: Thu, 19 Sep 2024 11:14:45 +0200 From: Mark Rutland To: Ard Biesheuvel Cc: Marc Zyngier , Will Deacon , syzbot , catalin.marinas@arm.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com, Nathan Chancellor , Nick Desaulniers , Bill Wendling , Justin Stitt Subject: Re: [syzbot] [arm?] upstream test error: KASAN: invalid-access Write in setup_arch Message-ID: References: <000000000000f362e80620e27859@google.com> <20240830095254.GA7769@willie-the-truck> <86wmjwvatn.wl-maz@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Thu, Sep 05, 2024 at 04:25:57PM +0200, Ard Biesheuvel wrote: > On Thu, 5 Sept 2024 at 16:03, Mark Rutland wrote: > > Putting the KASAN issue aside (which I'll handle in a separate thread), > > I think there is a real issue here with LLVM. > > > > What's going on here is that .idmap.text ends up more than 128M away > > from .head.text, so the 'b primary_entry' at the start of the Image > > isn't in range: > > > > | [mark@lakrids:~/src/linux]% usekorg 14.1.0 aarch64-linux-objdump -t vmlinux | grep -w _text > > | ffff800080000000 g .head.text 0000000000000000 _text > > | [mark@lakrids:~/src/linux]% usekorg 14.1.0 aarch64-linux-objdump -t vmlinux | grep -w primary_entry > > | ffff8000889df0e0 g .rodata.text 000000000000006c primary_entry > > > > ... as those are ~128MiB apart. > > > > When building with GCC those end up ~101MiB apart: > > > > | [mark@lakrids:~/src/linux]% usekorg 14.1.0 aarch64-linux-objdump -t vmlinux | grep -w _text > > | ffff800080000000 g .head.text 0000000000000000 _text > > | [mark@lakrids:~/src/linux]% usekorg 14.1.0 aarch64-linux-objdump -t vmlinux | grep -w primary_entry > > | ffff8000865ae0e0 g .rodata.text 000000000000006c primary_entry > > > > When that happens, LLD makes the header branch to a veneer/thunk: > > > > | ffff800080000000 <_text>: > > | ffff800080000000: fa405a4d ccmp x18, #0x0, #0xd, pl // pl = nfrst > > | ffff800080000004: 14003fff b ffff800080010000 <__AArch64AbsLongThunk_primary_entry> > > > > ... and unfortunately, that veneer/thunk uses a literal with the > > statically-linked TTBR1 address of primary_entry: > > > > | ffff800080010000 <__AArch64AbsLongThunk_primary_entry>: > > | ffff800080010000: 58000050 ldr x16, ffff800080010008 <__AArch64AbsLongThunk_primary_entry+0x8> > > | ffff800080010004: d61f0200 br x16 > > | ffff800080010008: 889df0e0 .word 0x889df0e0 > > | ffff80008001000c: ffff8000 .word 0xffff8000 > > > ... > > LLVM folk, is there any existing option to ask LLD to use ADRP+ADD for > > the veneer/thunk? ... and if not, would it be possible to add an option > > for that? > > > > ld.lld takes --pic-veneer, which (from looking at the llvm sources) > appears to do what we need here. Ah; now I take another look I see that's in the man page and is also supported by GNU LD, so I'll spin a patch to use that. Thanks for the pointer! Mark.