From mboxrd@z Thu Jan 1 00:00:00 1970 From: Kees Cook Subject: [PATCH v2 29/29] x86: Use INT3 instead of NOP for linker fill bytes Date: Thu, 10 Oct 2019 17:06:09 -0700 Message-ID: <20191011000609.29728-30-keescook@chromium.org> References: <20191011000609.29728-1-keescook@chromium.org> Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; h=from:to:cc:subject:date:message-id:in-reply-to:references; bh=Wn91QvvOWXGcdAukdBFPOsAS+V9wjbJFfxE/dszqFsM=; b=TKF/H7IXE7UJDzb3rMUleub9owN4KR+Kc5MridCe/6j0nlzZqoEI/zttKy0QHihDrJ 2ZeHmtUNHexo6bQLRtT0gDvTipRD0K5TGW8Q7FVWpvhcmLBUGnPT1TySO+nYDUITKTZu 3WNoDW0bVMFt0uCMT6eBCSnH00RkY54ViUTLk= In-Reply-To: <20191011000609.29728-1-keescook@chromium.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Borislav Petkov Cc: Kees Cook , Rick Edgecombe , Dave Hansen , Andy Lutomirski , Arnd Bergmann , Michael Ellerman , Heiko Carstens , Will Deacon , linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, linux-alpha@vger.kernel.org, linux-ia64@vger.kernel.org, linux-s390@vger.kernel.org, linux-c6x-dev@linux-c6x.org, Yoshinori Sato , Michal Simek , linux-parisc@vger.kernel.org, linux-xtensa@linux-xtensa.org, x86@kernel.org, linux-kernel@vger.kernel.org Instead of using 0x90 (NOP) to fill bytes between functions, which makes it easier to sloppily target functions in function pointer overwrite attacks, fill with 0xCC (INT3) to force a trap. Also drop the space between "=" and the value to better match the binutils documentation https://sourceware.org/binutils/docs/ld/Output-Section-Fill.html#Output-Section-Fill Example "objdump -d" before: ... ffffffff810001e0 : ffffffff810001e0: 48 8b 25 e1 b1 51 01 mov 0x151b1e1(%rip),%rsp # ffffffff8251b3c8 ffffffff810001e7: e9 d5 fe ff ff jmpq ffffffff810000c1 ffffffff810001ec: 90 nop ffffffff810001ed: 90 nop ffffffff810001ee: 90 nop ffffffff810001ef: 90 nop ffffffff810001f0 <__startup_64>: ... After: ... ffffffff810001e0 : ffffffff810001e0: 48 8b 25 41 79 53 01 mov 0x1537941(%rip),%rsp # ffffffff82537b28 ffffffff810001e7: e9 d5 fe ff ff jmpq ffffffff810000c1 ffffffff810001ec: cc int3 ffffffff810001ed: cc int3 ffffffff810001ee: cc int3 ffffffff810001ef: cc int3 ffffffff810001f0 <__startup_64>: ... Signed-off-by: Kees Cook --- arch/x86/kernel/vmlinux.lds.S | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S index b06d6e1188de..3a1a819da137 100644 --- a/arch/x86/kernel/vmlinux.lds.S +++ b/arch/x86/kernel/vmlinux.lds.S @@ -144,7 +144,7 @@ SECTIONS *(.text.__x86.indirect_thunk) __indirect_thunk_end = .; #endif - } :text = 0x9090 + } :text =0xcccc /* End of text section, which should occupy whole number of pages */ _etext = .; -- 2.17.1