From mboxrd@z Thu Jan 1 00:00:00 1970 From: Kees Cook Subject: [PATCH 29/29] x86: Use INT3 instead of NOP for linker fill bytes Date: Thu, 26 Sep 2019 10:56:02 -0700 Message-ID: <20190926175602.33098-30-keescook@chromium.org> References: <20190926175602.33098-1-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=yn5wfwJoFu2XxkEapi5oUode7Z6ofSq2WooR/oMOeig=; b=GIG4pntI4mSLZBUOLoFMk4guSw8F6GtVAwhEFiBddEsAgwrkRwPjIGbLRlxFjf3FFl AAkc2fNz+FhNHp9iA1Gn1CLcywcbJ+TQMeOOKdi3rLClFQao449j+D61pfii2Lo6mCp9 gdFOurgujqWI728AB8TNIMWAJHUqnNxeyVafk= In-Reply-To: <20190926175602.33098-1-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: Thomas Gleixner Cc: Kees Cook , Rick Edgecombe , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" , Dave Hansen , Andy Lutomirski , Arnd Bergmann , linux-arch@vger.kernel.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 drops 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 a5c8571e4967..a37817fafb22 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