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[198.0.35.241]) by smtp.gmail.com with ESMTPSA id v15-20020a62a50f000000b006528d9080f6sm5450990pfm.9.2023.06.30.11.27.00 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 30 Jun 2023 11:27:00 -0700 (PDT) Date: Fri, 30 Jun 2023 11:26:59 -0700 From: Kees Cook To: Sami Tolvanen Cc: Paul Walmsley , Palmer Dabbelt , Albert Ou , Nathan Chancellor , Nick Desaulniers , linux-riscv@lists.infradead.org, llvm@lists.linux.dev, linux-kernel@vger.kernel.org Subject: Re: [PATCH 4/6] riscv: Add CFI error handling Message-ID: <202306301126.D7EC815A22@keescook> References: <20230629234244.1752366-8-samitolvanen@google.com> <20230629234244.1752366-12-samitolvanen@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230629234244.1752366-12-samitolvanen@google.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jun 29, 2023 at 11:42:49PM +0000, Sami Tolvanen wrote: > With CONFIG_CFI_CLANG, the compiler injects a type preamble immediately > before each function and a check to validate the target function type > before indirect calls: > > ; type preamble > .word > function: > ... > ; indirect call check > lw t1, -4(a0) > lui t2, > addiw t2, t2, > beq t1, t2, .Ltmp0 > ebreak > .Ltmp0: > jarl a0 > > Implement error handling code for the ebreak traps emitted for the > checks. This produces the following oops on a CFI failure (generated > using lkdtm): > > [ 21.177245] CFI failure at lkdtm_indirect_call+0x22/0x32 [lkdtm] > (target: lkdtm_increment_int+0x0/0x18 [lkdtm]; expected type: 0x3ad55aca) > [ 21.178483] Kernel BUG [#1] > [ 21.178671] Modules linked in: lkdtm > [ 21.179037] CPU: 1 PID: 104 Comm: sh Not tainted > 6.3.0-rc6-00037-g37d5ec6297ab #1 > [ 21.179511] Hardware name: riscv-virtio,qemu (DT) > [ 21.179818] epc : lkdtm_indirect_call+0x22/0x32 [lkdtm] > [ 21.180106] ra : lkdtm_CFI_FORWARD_PROTO+0x48/0x7c [lkdtm] > [ 21.180426] epc : ffffffff01387092 ra : ffffffff01386f14 sp : ff20000000453cf0 > [ 21.180792] gp : ffffffff81308c38 tp : ff6000000243f080 t0 : ff20000000453b78 > [ 21.181157] t1 : 000000003ad55aca t2 : 000000007e0c52a5 s0 : ff20000000453d00 > [ 21.181506] s1 : 0000000000000001 a0 : ffffffff0138d170 a1 : ffffffff013870bc > [ 21.181819] a2 : b5fea48dd89aa700 a3 : 0000000000000001 a4 : 0000000000000fff > [ 21.182169] a5 : 0000000000000004 a6 : 00000000000000b7 a7 : 0000000000000000 > [ 21.182591] s2 : ff20000000453e78 s3 : ffffffffffffffea s4 : 0000000000000012 > [ 21.183001] s5 : ff600000023c7000 s6 : 0000000000000006 s7 : ffffffff013882a0 > [ 21.183653] s8 : 0000000000000008 s9 : 0000000000000002 s10: ffffffff0138d878 > [ 21.184245] s11: ffffffff0138d878 t3 : 0000000000000003 t4 : 0000000000000000 > [ 21.184591] t5 : ffffffff8133df08 t6 : ffffffff8133df07 > [ 21.184858] status: 0000000000000120 badaddr: 0000000000000000 > cause: 0000000000000003 > [ 21.185415] [] lkdtm_indirect_call+0x22/0x32 [lkdtm] > [ 21.185772] [] lkdtm_CFI_FORWARD_PROTO+0x48/0x7c [lkdtm] > [ 21.186093] [] lkdtm_do_action+0x22/0x34 [lkdtm] > [ 21.186445] [] direct_entry+0x128/0x13a [lkdtm] > [ 21.186817] [] full_proxy_write+0x58/0xb2 > [ 21.187352] [] vfs_write+0x14c/0x33a > [ 21.187644] [] ksys_write+0x64/0xd4 > [ 21.187832] [] sys_write+0xe/0x1a > [ 21.188171] [] ret_from_syscall+0x0/0x2 > [ 21.188595] Code: 0513 0f65 a303 ffc5 53b7 7e0c 839b 2a53 0363 0073 (9002) 9582 > [ 21.189178] ---[ end trace 0000000000000000 ]--- > [ 21.189590] Kernel panic - not syncing: Fatal exception > > Signed-off-by: Sami Tolvanen Looks good -- should the noaddr failure paths include any warnings of their own? (i.e. isn't that unexpected?) Reviewed-by: Kees Cook -- Kees Cook