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From: Kees Cook <keescook@chromium.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Kees Cook <keescook@chromium.org>,
	Rick Edgecombe <rick.p.edgecombe@intel.com>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Andy Lutomirski <luto@kernel.org>, Arnd Bergmann <arnd@arndb.de>,
	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 <ysato@users.sourceforge.jp>,
	Michal Simek <monstr@monstr.eu>,
	linux-parisc@vger.kernel.org, linux-xtensa@linux-xtensa.org,
	x86@kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH 29/29] x86: Use INT3 instead of NOP for linker fill bytes
Date: Thu, 26 Sep 2019 10:56:02 -0700	[thread overview]
Message-ID: <20190926175602.33098-30-keescook@chromium.org> (raw)
In-Reply-To: <20190926175602.33098-1-keescook@chromium.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 <start_cpu0>:
ffffffff810001e0:       48 8b 25 e1 b1 51 01    mov 0x151b1e1(%rip),%rsp        # ffffffff8251b3c8 <initial_stack>
ffffffff810001e7:       e9 d5 fe ff ff          jmpq   ffffffff810000c1 <secondary_startup_64+0x91>
ffffffff810001ec:       90                      nop
ffffffff810001ed:       90                      nop
ffffffff810001ee:       90                      nop
ffffffff810001ef:       90                      nop

ffffffff810001f0 <__startup_64>:
...

After:

...
ffffffff810001e0 <start_cpu0>:
ffffffff810001e0:       48 8b 25 41 79 53 01    mov 0x1537941(%rip),%rsp        # ffffffff82537b28 <initial_stack>
ffffffff810001e7:       e9 d5 fe ff ff          jmpq   ffffffff810000c1 <secondary_startup_64+0x91>
ffffffff810001ec:       cc                      int3
ffffffff810001ed:       cc                      int3
ffffffff810001ee:       cc                      int3
ffffffff810001ef:       cc                      int3

ffffffff810001f0 <__startup_64>:
...

Signed-off-by: Kees Cook <keescook@chromium.org>
---
 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


  parent reply	other threads:[~2019-09-26 17:56 UTC|newest]

Thread overview: 42+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-09-26 17:55 [PATCH 00/29] vmlinux.lds.h: Refactor EXCEPTION_TABLE and NOTES Kees Cook
2019-09-26 17:55 ` [PATCH 01/29] powerpc: Rename "notes" PT_NOTE to "note" Kees Cook
2019-09-26 17:55 ` [PATCH 02/29] powerpc: Remove PT_NOTE workaround Kees Cook
2019-09-26 17:55 ` [PATCH 03/29] powerpc: Rename PT_LOAD identifier "kernel" to "text" Kees Cook
2019-09-26 17:55 ` [PATCH 04/29] alpha: " Kees Cook
2019-09-26 17:55 ` [PATCH 05/29] ia64: Rename PT_LOAD identifier "code" " Kees Cook
2019-09-26 17:55 ` [PATCH 06/29] s390: Move RO_DATA into "text" PT_LOAD Program Header Kees Cook
2019-09-26 17:55 ` [PATCH 07/29] x86: Restore "text" Program Header with dummy section Kees Cook
2019-10-10 10:33   ` Borislav Petkov
2019-10-10 16:46     ` Kees Cook
2019-09-26 17:55 ` [PATCH 08/29] vmlinux.lds.h: Provide EMIT_PT_NOTE to indicate export of .notes Kees Cook
2019-10-10 10:40   ` Borislav Petkov
2019-09-26 17:55 ` [PATCH 09/29] vmlinux.lds.h: Move Program Header restoration into NOTES macro Kees Cook
2019-09-26 17:55 ` [PATCH 10/29] vmlinux.lds.h: Move NOTES into RO_DATA Kees Cook
2019-09-26 17:55 ` [PATCH 11/29] vmlinux.lds.h: Replace RODATA with RO_DATA Kees Cook
2019-09-26 17:55 ` [PATCH 12/29] vmlinux.lds.h: Replace RO_DATA_SECTION " Kees Cook
2019-09-26 17:55 ` [PATCH 13/29] vmlinux.lds.h: Replace RW_DATA_SECTION with RW_DATA Kees Cook
2019-09-26 17:55 ` [PATCH 14/29] vmlinux.lds.h: Allow EXCEPTION_TABLE to live in RO_DATA Kees Cook
2019-10-01  9:05   ` Will Deacon
2019-10-10 15:25   ` Borislav Petkov
2019-10-10 16:47     ` Kees Cook
2019-09-26 17:55 ` [PATCH 15/29] x86: Actually use _etext for end of text segment Kees Cook
2019-09-26 17:55 ` [PATCH 16/29] x86: Move EXCEPTION_TABLE to RO_DATA segment Kees Cook
2019-09-26 17:55 ` [PATCH 17/29] alpha: " Kees Cook
2019-09-26 17:55 ` [PATCH 18/29] arm64: " Kees Cook
2019-10-01  9:03   ` Will Deacon
2019-10-01 15:48     ` Kees Cook
2019-09-26 17:55 ` [PATCH 19/29] c6x: " Kees Cook
2019-09-26 17:55 ` [PATCH 20/29] h8300: " Kees Cook
2019-09-26 17:55 ` [PATCH 21/29] ia64: " Kees Cook
2019-09-26 17:55 ` [PATCH 22/29] microblaze: " Kees Cook
2019-09-26 17:55 ` [PATCH 23/29] parisc: " Kees Cook
2019-09-26 17:55 ` [PATCH 24/29] powerpc: " Kees Cook
2019-09-26 17:55 ` [PATCH 25/29] xtensa: " Kees Cook
2019-09-26 17:55 ` [PATCH 26/29] x86/mm: Remove redundant &s on addresses Kees Cook
2019-09-26 17:56 ` [PATCH 27/29] x86/mm: Report which part of kernel image is freed Kees Cook
2019-09-26 17:56 ` [PATCH 28/29] x86/mm: Report actual image regions in /proc/iomem Kees Cook
2019-10-10 18:00   ` Borislav Petkov
2019-09-26 17:56 ` Kees Cook [this message]
2019-10-10 18:03 ` [PATCH 00/29] vmlinux.lds.h: Refactor EXCEPTION_TABLE and NOTES Borislav Petkov
2019-10-10 23:57   ` Kees Cook
2019-10-11  1:38     ` hpa

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