commit 11bf9b865898961cee60a41c483c9f27ec76e12e upstream.
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 class on ARM as well 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 david.brown@linaro.org Signed-off-by: Kees Cook keescook@chromium.org Cc: Andy Lutomirski luto@amacapital.net Cc: Arnd Bergmann arnd@arndb.de Cc: Borislav Petkov bp@alien8.de Cc: Brad Spengler spender@grsecurity.net Cc: Brian Gerst brgerst@gmail.com Cc: Denys Vlasenko dvlasenk@redhat.com Cc: Emese Revfy re.emese@gmail.com Cc: H. Peter Anvin hpa@zytor.com Cc: Linus Torvalds torvalds@linux-foundation.org Cc: Mathias Krause minipli@googlemail.com Cc: Michael Ellerman mpe@ellerman.id.au Cc: Nathan Lynch nathan_lynch@mentor.com Cc: PaX Team pageexec@freemail.hu Cc: Peter Zijlstra peterz@infradead.org Cc: Russell King linux@arm.linux.org.uk Cc: Thomas Gleixner tglx@linutronix.de Cc: kernel-hardening@lists.openwall.com Cc: linux-arch linux-arch@vger.kernel.org Cc: linux-arm-kernel@lists.infradead.org Cc: linux-kernel@vger.kernel.org Link: http://lkml.kernel.org/r/1455748879-21872-8-git-send-email-keescook@chromium... Signed-off-by: Ingo Molnar mingo@kernel.org --- 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 b2b97e3..a62a7b6 100644 --- a/arch/arm/vdso/vdso.S +++ b/arch/arm/vdso/vdso.S @@ -23,9 +23,8 @@ #include <linux/const.h> #include <asm/page.h>
- __PAGE_ALIGNED_DATA - .globl vdso_start, vdso_end + .section .data..ro_after_init .balign PAGE_SIZE vdso_start: .incbin "arch/arm/vdso/vdso.so"