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Mon, 27 Apr 2020 13:45:52 -0700 (PDT) Date: Mon, 27 Apr 2020 13:45:46 -0700 From: Sami Tolvanen To: Will Deacon Subject: Re: [PATCH v11 01/12] add support for Clang's Shadow Call Stack (SCS) Message-ID: <20200427204546.GA80713@google.com> References: <20191018161033.261971-1-samitolvanen@google.com> <20200416161245.148813-1-samitolvanen@google.com> <20200416161245.148813-2-samitolvanen@google.com> <20200420171727.GB24386@willie-the-truck> <20200420211830.GA5081@google.com> <20200422173938.GA3069@willie-the-truck> <20200422235134.GA211149@google.com> <202004231121.A13FDA100@keescook> <20200424112113.GC21141@willie-the-truck> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20200424112113.GC21141@willie-the-truck> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200427_134556_330145_6C3244B3 X-CRM114-Status: GOOD ( 20.03 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Mark Rutland , Juri Lelli , kernel-hardening@lists.openwall.com, Peter Zijlstra , Catalin Marinas , Marc Zyngier , Masahiro Yamada , clang-built-linux@googlegroups.com, Ingo Molnar , Laura Abbott , Dave Martin , Kees Cook , Jann Horn , Steven Rostedt , linux-arm-kernel@lists.infradead.org, Michal Marek , Ard Biesheuvel , Nick Desaulniers , linux-kernel@vger.kernel.org, Miguel Ojeda , James Morse , Masami Hiramatsu Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Fri, Apr 24, 2020 at 12:21:14PM +0100, Will Deacon wrote: > Also, since you mentioned the lack of redzoning, isn't it a bit dodgy > allocating blindly out of the kmem_cache? It means we don't have a redzone > or a guard page, so if you can trigger something like a recursion bug then > could you scribble past the SCS before the main stack overflows? Would this > clobber somebody else's SCS? I agree that allocating from a kmem_cache isn't ideal for safety. It's a compromise to reduce memory overhead. > The vmap version that I asked Sami to drop > is at least better in this regard, although the guard page is at the wrong > end of the stack and we just hope that the allocation below us didn't pass > VM_NO_GUARD. Looks like the same story for vmap stack :/ SCS grows up and the guard page is after the allocation, so how is it at the wrong end? Am I missing something here? > If we split the pointer in two (base, offset) then we could leave the > base live in the thread_info, not require alignment of the stacks (which > may allow for unconditional redzoning?) and then just update the offset > value on context switch, which could be trivially checked as part of the > existing stack overflow checking on kernel entry. I sent out v13 with split pointers, but I'm not sure it's convenient to add an overflow check to kernel_ventry where the VMAP_STACK check is done. I suppose I could add a check to kernel_entry after we load x18 from tsk. Thoughts? Sami _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel