From mboxrd@z Thu Jan 1 00:00:00 1970 From: david.brown@linaro.org (David Brown) Date: Tue, 16 Feb 2016 14:36:59 -0700 Subject: [PATCH] ARM: vdso: Mark vDSO code as read-only In-Reply-To: <1453226922-16831-1-git-send-email-keescook@chromium.org> References: <1453226922-16831-1-git-send-email-keescook@chromium.org> Message-ID: <20160216213659.GA47194@davidb.org> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org 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 at 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 at 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 --- This patch depends on Kees Cook's series https://lkml.org/lkml/2016/1/19/497 which adds the ro_after_init section. 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 #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" -- 2.7.1