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[209.85.208.171]) by smtp.gmail.com with ESMTPSA id e14sm621450ljj.120.2020.08.27.11.15.28 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 27 Aug 2020 11:15:28 -0700 (PDT) Received: by mail-lj1-f171.google.com with SMTP id g6so7469591ljn.11 for ; Thu, 27 Aug 2020 11:15:28 -0700 (PDT) X-Received: by 2002:a2e:92d0:: with SMTP id k16mr9604351ljh.70.1598552128279; Thu, 27 Aug 2020 11:15:28 -0700 (PDT) MIME-Version: 1.0 References: <20200827150030.282762-1-hch@lst.de> <20200827150030.282762-9-hch@lst.de> In-Reply-To: <20200827150030.282762-9-hch@lst.de> From: Linus Torvalds Date: Thu, 27 Aug 2020 11:15:12 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH 08/10] x86: remove address space overrides using set_fs() To: Christoph Hellwig Cc: Al Viro , Michael Ellerman , "the arch/x86 maintainers" , Kees Cook , Linux Kernel Mailing List , linux-fsdevel , linux-arch , linuxppc-dev Content-Type: text/plain; charset="UTF-8" Sender: linux-arch-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-arch@vger.kernel.org On Thu, Aug 27, 2020 at 8:00 AM Christoph Hellwig wrote: > > SYM_FUNC_START(__get_user_2) > add $1,%_ASM_AX > jc bad_get_user This no longer makes sense, and > - mov PER_CPU_VAR(current_task), %_ASM_DX > - cmp TASK_addr_limit(%_ASM_DX),%_ASM_AX > + LOAD_TASK_SIZE_MAX > + cmp %_ASM_DX,%_ASM_AX This should be LOAD_TASK_SIZE_MAX_MINUS_N(1) cmp %_ASM_DX,%_ASM_AX instead (and then because we no longer modify _ASM_AX, we'd also remove the offset on the access). > SYM_FUNC_START(__put_user_2) > - ENTER > - mov TASK_addr_limit(%_ASM_BX),%_ASM_BX > + LOAD_TASK_SIZE_MAX > sub $1,%_ASM_BX It's even more obvious here. We load a constant and then immediately do a "sub $1" on that value. It's not a huge deal, you don't have to respin the series for this, I just wanted to point it out so that people are aware of it and if I forget somebody else will hopefully remember that "we should fix that too". Linus