From mboxrd@z Thu Jan 1 00:00:00 1970 Reply-To: kernel-hardening@lists.openwall.com From: Kees Cook Date: Wed, 17 Feb 2016 14:41:18 -0800 Message-Id: <1455748879-21872-8-git-send-email-keescook@chromium.org> In-Reply-To: <1455748879-21872-1-git-send-email-keescook@chromium.org> References: <1455748879-21872-1-git-send-email-keescook@chromium.org> Subject: [kernel-hardening] [PATCH v5 7/7] ARM: vdso: Mark vDSO code as read-only To: Ingo Molnar Cc: Kees Cook , David Brown , Andy Lutomirski , "H. Peter Anvin" , Michael Ellerman , Mathias Krause , Thomas Gleixner , x86@kernel.org, Arnd Bergmann , PaX Team , Emese Revfy , kernel-hardening@lists.openwall.com, linux-kernel@vger.kernel.org, linux-arch List-ID: From: David Brown Although the arm vDSO is cleanly separated by code/data with the code being read-only in userspace mappings, the code page is still writable from the kernel. There have been exploits (such as http://itszn.com/blog/?p=21) that take advantage of this on x86 to go from a bad kernel write to full root. Prevent this specific exploit on arm by putting the vDSO code page in post-init read-only memory as well. Before: vdso: 1 text pages at base 80927000 root@Vexpress:/ cat /sys/kernel/debug/kernel_page_tables ---[ Modules ]--- ---[ Kernel Mapping ]--- 0x80000000-0x80100000 1M RW NX SHD 0x80100000-0x80600000 5M ro x SHD 0x80600000-0x80800000 2M ro NX SHD 0x80800000-0xbe000000 984M RW NX SHD After: vdso: 1 text pages at base 8072b000 root@Vexpress:/ cat /sys/kernel/debug/kernel_page_tables ---[ Modules ]--- ---[ Kernel Mapping ]--- 0x80000000-0x80100000 1M RW NX SHD 0x80100000-0x80600000 5M ro x SHD 0x80600000-0x80800000 2M ro NX SHD 0x80800000-0xbe000000 984M RW NX SHD Inspired by https://lkml.org/lkml/2016/1/19/494 based on work by the PaX Team, Brad Spengler, and Kees Cook. Signed-off-by: David Brown Acked-by: Kees Cook --- arch/arm/vdso/vdso.S | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) diff --git a/arch/arm/vdso/vdso.S b/arch/arm/vdso/vdso.S index b2b97e3e7bab..a62a7b64f49c 100644 --- a/arch/arm/vdso/vdso.S +++ b/arch/arm/vdso/vdso.S @@ -23,9 +23,8 @@ #include #include - __PAGE_ALIGNED_DATA - .globl vdso_start, vdso_end + .section .data..ro_after_init .balign PAGE_SIZE vdso_start: .incbin "arch/arm/vdso/vdso.so" -- 2.6.3