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Wed, 13 Oct 2021 17:44:38 -0700 (PDT) X-Google-Smtp-Source: ABdhPJxN7hRCKU/SKDN5he5DTJoX8aHISMFYBLbyiwc6It64vOfVpkP2EJr4BFnCIqPmfMZ5NSu/ig== X-Received: by 2002:a37:b742:: with SMTP id h63mr2191187qkf.204.1634172277891; Wed, 13 Oct 2021 17:44:37 -0700 (PDT) Received: from treble ([2600:1700:6e32:6c00::15]) by smtp.gmail.com with ESMTPSA id z19sm701005qts.96.2021.10.13.17.44.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 13 Oct 2021 17:44:37 -0700 (PDT) Date: Wed, 13 Oct 2021 17:44:34 -0700 From: Josh Poimboeuf To: Sami Tolvanen Cc: x86@kernel.org, Kees Cook , Peter Zijlstra , Nathan Chancellor , Nick Desaulniers , Sedat Dilek , Steven Rostedt , linux-hardening@vger.kernel.org, linux-kernel@vger.kernel.org, llvm@lists.linux.dev Subject: Re: [PATCH v5 01/15] objtool: Add CONFIG_CFI_CLANG support Message-ID: <20211014004434.vjbpkd4ykn7upvsw@treble> References: <20211013181658.1020262-1-samitolvanen@google.com> <20211013181658.1020262-2-samitolvanen@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20211013181658.1020262-2-samitolvanen@google.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Oct 13, 2021 at 11:16:44AM -0700, Sami Tolvanen wrote: > The upcoming CONFIG_CFI_CLANG support uses -fsanitize=cfi, the > non-canonical version of which hijacks function entry by changing > function relocation references to point to an intermediary jump table. > > For example: > > Relocation section '.rela.discard.func_stack_frame_non_standard' at offset 0x37e018 contains 6 entries: > Offset Info Type Symbol's Value Symbol's Name + Addend > 0000000000000000 0002944700000002 R_X86_64_PC32 00000000000023f0 do_suspend_lowlevel + 0 > 0000000000000008 0003c11900000001 R_X86_64_64 0000000000000008 xen_cpuid$e69bc59f4fade3b6f2b579b3934137df.cfi_jt + 0 > 0000000000000010 0003980900000001 R_X86_64_64 0000000000000060 machine_real_restart.cfi_jt + 0 > 0000000000000018 0003962b00000001 R_X86_64_64 0000000000000e18 kretprobe_trampoline.cfi_jt + 0 > 0000000000000020 000028f300000001 R_X86_64_64 0000000000000000 .rodata + 12 > 0000000000000028 000349f400000001 R_X86_64_64 0000000000000018 __crash_kexec.cfi_jt + 0 > > 0000000000000060 : > 60: e9 00 00 00 00 jmpq 65 > 61: R_X86_64_PLT32 machine_real_restart-0x4 > 65: cc int3 > 66: cc int3 > 67: cc int3 > > This breaks objtool vmlinux validation in many ways, including static > call site detection and the STACK_FRAME_NON_STANDARD() macro. > > Fix it by converting those relocations' symbol references back to their > original non-jump-table versions. Note this doesn't change the actual > relocations in the object itself, it just changes objtool's view of > them. This change is based on Josh's initial patch: > > https://lore.kernel.org/r/d743f4b36e120c06506567a9f87a062ae03da47f.1611263462.git.jpoimboe@redhat.com/ > > Reported-by: Sedat Dilek > Suggested-by: Josh Poimboeuf > Signed-off-by: Sami Tolvanen > Reviewed-by: Nick Desaulniers > Tested-by: Nick Desaulniers > Tested-by: Sedat Dilek Acked-by: Josh Poimboeuf -- Josh