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 4F28512E61 for ; Fri, 29 Mar 2024 01:39:34 +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=1711676375; cv=none; b=IRXkw36sDtSsA80hqEBKU7tMuSyJQZ/Z3PHi42HrKYuD0YI5aKxYcVPy3Emk6qHv0oAHrcNqnk4ggzauCBk4sNhWtVvieoNAMn+7pUoPnue8huD1b27SvLR9iVBD4jpiHGyYD4nOVmcNT2ELvd5n4NgcwnuUp73BIv/hUUp0pUk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1711676375; c=relaxed/simple; bh=a5ieawO8SQeApeL9oKybsPxEd82dEmDBRDRIxBwjcRs=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=hSzyKInIVrm4n54JYSRYJzdjg+BDh09a+pdI8OfRZpPLLQaPDOXtxLQL4m9ZNFWLhUdMbIKy/5W595dh04eFj4a4seUTNl1X+nYC4oQl3S+xASepdXwC4nSY4AsLeXri4xWhq1Ea3tjfQNI4+Nxw44VaMJhv0/kGLX1LG9den8c= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=kmrNDWe7; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="kmrNDWe7" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B1159C433C7; Fri, 29 Mar 2024 01:39:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1711676374; bh=a5ieawO8SQeApeL9oKybsPxEd82dEmDBRDRIxBwjcRs=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=kmrNDWe7VC2Iv6v7c0lpVD7a5pC8MGsELcd3loeJEUQ/m9S9kcIVYTwePNyflMFgI Cx8JBaKTvJR8p3Bs6VBPaZWa+Y4PN87vGDcbDVfn2E6MI3rEx7a8pZ8OhLI6BRSlfe jwHginDeJnwlzT9xEP/zVKLcothlgnvpy6eE9AqL++177/+a66WtlZ/vy9iuj2bKyb Ab0G03yW32mWB6pwqJEAkTjZh4ln9WCfwW06/0MlL+PCcHgokeV+FP67Ew+MyUKAg2 hlt55mBJNB2Y6/kx+IjxbfBAzroof28eAUdntZ1CBLAscatZqHk4Av83oZcnPNI+bq Mjk3xIUDlX4oA== Date: Thu, 28 Mar 2024 18:39:32 -0700 From: Josh Poimboeuf To: Alexandre Chartre Cc: linux-kernel@vger.kernel.org, peterz@infradead.org Subject: Re: [PATCH] objtool/x86: objtool can confuse memory and stack access Message-ID: <20240329013932.vxqzc74szrckxqdq@treble> References: <20240328134634.350592-1-alexandre.chartre@oracle.com> 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=utf-8 Content-Disposition: inline In-Reply-To: <20240328134634.350592-1-alexandre.chartre@oracle.com> On Thu, Mar 28, 2024 at 02:46:34PM +0100, Alexandre Chartre wrote: > The encoding of an x86 instruction can include a ModR/M and a SIB > (Scale-Index-Base) byte to describe the addressing mode of the > instruction. > > objtool processes all addressing mode with a SIB base of 5 as having > %rbp as the base register. However, a SIB base of 5 means that the > effective address has either no base (if ModR/M mod is zero) or %rbp > as the base (if ModR/M mod is 1 or 2). This can cause objtool to confuse > an absolute address access with a stack operation. > > For example, objtool will see the following instruction: > > 4c 8b 24 25 e0 ff ff mov 0xffffffffffffffe0,%r12 > > as a stack operation (i.e. similar to: mov -0x20(%rbp), %r12). > > [Note that this kind of weird absolute address access is added by the > compiler when using KASAN.] > > If this perceived stack operation happens to reference the location > where %r12 was pushed on the stack then the objtool validation will > think that %r12 is being restored and this can cause a stack state > mismatch. > > This kind behavior was seen on xfs code, after a minor change (convert > kmem_alloc() to kmalloc()): > > >> fs/xfs/xfs.o: warning: objtool: xfs_da_grow_inode_int+0x6c1: stack state mismatch: reg1[12]=-2-48 reg2[12]=-1+0 > > Reported-by: kernel test robot > Closes: https://lore.kernel.org/oe-kbuild-all/202402220435.MGN0EV6l-lkp@intel.com/ > Signed-off-by: Alexandre Chartre Nice, thanks for finding and debugging this. Would it make sense to make the check more generic by putting it into rm_is()? -- Josh