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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id b22sm9843692pju.26.2020.07.31.16.08.30 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 31 Jul 2020 16:08:30 -0700 (PDT) From: Kees Cook To: Thomas Gleixner , Will Deacon Subject: [PATCH v5 01/36] x86/boot/compressed: Move .got.plt entries out of the .got section Date: Fri, 31 Jul 2020 16:07:45 -0700 Message-Id: <20200731230820.1742553-2-keescook@chromium.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20200731230820.1742553-1-keescook@chromium.org> References: <20200731230820.1742553-1-keescook@chromium.org> MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200731_190836_700512_4027242E X-CRM114-Status: GOOD ( 18.71 ) X-Spam-Score: -0.2 (/) X-Spam-Report: SpamAssassin version 3.4.4 on merlin.infradead.org summary: Content analysis details: (-0.2 points) pts rule name description ---- ---------------------- -------------------------------------------------- -0.0 RCVD_IN_DNSWL_NONE RBL: Sender listed at https://www.dnswl.org/, no trust [2607:f8b0:4864:20:0:0:0:641 listed in] [list.dnswl.org] -0.0 SPF_PASS SPF: sender matches SPF record 0.0 SPF_HELO_NONE SPF: HELO does not publish an SPF Record -0.1 DKIM_VALID_EF Message has a valid DKIM or DK signature from envelope-from domain 0.1 DKIM_SIGNED Message has a DKIM or DK signature, not necessarily valid -0.1 DKIM_VALID Message has at least one valid DKIM or DK signature -0.1 DKIM_VALID_AU Message has a valid DKIM or DK signature from author's domain -0.0 DKIMWL_WL_HIGH DKIMwl.org - Whitelisted High sender 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 , linux-arch@vger.kernel.org, linux-efi@vger.kernel.org, Kees Cook , Arnd Bergmann , Catalin Marinas , Masahiro Yamada , x86@kernel.org, Nick Desaulniers , Russell King , linux-kernel@vger.kernel.org, clang-built-linux@googlegroups.com, Arvind Sankar , Ingo Molnar , James Morse , Sedat Dilek , Nathan Chancellor , Borislav Petkov , Peter Collingbourne , Ard Biesheuvel , linux-arm-kernel@lists.infradead.org Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+patchwork-linux-arm=patchwork.kernel.org@lists.infradead.org From: Ard Biesheuvel The .got.plt section contains the part of the GOT which is used by PLT entries, and which gets updated lazily by the dynamic loader when function calls are dispatched through those PLT entries. On fully linked binaries such as the kernel proper or the decompressor, this never happens, and so in practice, the .got.plt section consists only of the first 3 magic entries that are meant to point at the _DYNAMIC section and at the fixup routine in the loader. However, since we don't use a dynamic loader, those entries are never populated or used. This means that treating those entries like ordinary GOT entries, and updating their values based on the actual placement of the executable in memory is completely pointless, and we can just ignore the .got.plt section entirely, provided that it has no additional entries beyond the first 3 ones. So add an assertion in the linker script to ensure that this assumption holds, and move the contents out of the [_got, _egot) memory range that is modified by the GOT fixup routines. While at it, drop the KEEP(), since it has no effect on the contents of output sections that are created by the linker itself. Signed-off-by: Ard Biesheuvel Signed-off-by: Arvind Sankar Tested-by: Sedat Dilek Tested-by: Nick Desaulniers Reviewed-by: Kees Cook Acked-by: Arvind Sankar Link: https://lore.kernel.org/r/20200523120021.34996-2-ardb@kernel.org Signed-off-by: Kees Cook --- arch/x86/boot/compressed/vmlinux.lds.S | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) diff --git a/arch/x86/boot/compressed/vmlinux.lds.S b/arch/x86/boot/compressed/vmlinux.lds.S index 8f1025d1f681..b17d218ccdf9 100644 --- a/arch/x86/boot/compressed/vmlinux.lds.S +++ b/arch/x86/boot/compressed/vmlinux.lds.S @@ -44,10 +44,13 @@ SECTIONS } .got : { _got = .; - KEEP(*(.got.plt)) KEEP(*(.got)) _egot = .; } + .got.plt : { + *(.got.plt) + } + .data : { _data = . ; *(.data) @@ -77,3 +80,9 @@ SECTIONS DISCARDS } + +#ifdef CONFIG_X86_64 +ASSERT(SIZEOF(.got.plt) == 0 || SIZEOF(.got.plt) == 0x18, "Unexpected GOT/PLT entries detected!") +#else +ASSERT(SIZEOF(.got.plt) == 0 || SIZEOF(.got.plt) == 0xc, "Unexpected GOT/PLT entries detected!") +#endif