From: Kees Cook Date: Wed, 17 Feb 2016 22:41:17 +0000 (-0800) Subject: x86/vdso: Mark the vDSO code read-only after init X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=018ef8dcf3de5f62e2cc1a9273cc27e1c6ba8de5;p=GitHub%2FLineageOS%2FG12%2Fandroid_kernel_amlogic_linux-4.9.git x86/vdso: Mark the vDSO code read-only after init The vDSO does not need to be writable after __init, so mark it as __ro_after_init. The result kills the exploit method of writing to the vDSO from kernel space resulting in userspace executing the modified code, as shown here to bypass SMEP restrictions: http://itszn.com/blog/?p=21 The memory map (with added vDSO address reporting) shows the vDSO moving into read-only memory: Before: [ 0.143067] vDSO @ ffffffff82004000 [ 0.143551] vDSO @ ffffffff82006000 ---[ High Kernel Mapping ]--- 0xffffffff80000000-0xffffffff81000000 16M pmd 0xffffffff81000000-0xffffffff81800000 8M ro PSE GLB x pmd 0xffffffff81800000-0xffffffff819f3000 1996K ro GLB x pte 0xffffffff819f3000-0xffffffff81a00000 52K ro NX pte 0xffffffff81a00000-0xffffffff81e00000 4M ro PSE GLB NX pmd 0xffffffff81e00000-0xffffffff81e05000 20K ro GLB NX pte 0xffffffff81e05000-0xffffffff82000000 2028K ro NX pte 0xffffffff82000000-0xffffffff8214f000 1340K RW GLB NX pte 0xffffffff8214f000-0xffffffff82281000 1224K RW NX pte 0xffffffff82281000-0xffffffff82400000 1532K RW GLB NX pte 0xffffffff82400000-0xffffffff83200000 14M RW PSE GLB NX pmd 0xffffffff83200000-0xffffffffc0000000 974M pmd After: [ 0.145062] vDSO @ ffffffff81da1000 [ 0.146057] vDSO @ ffffffff81da4000 ---[ High Kernel Mapping ]--- 0xffffffff80000000-0xffffffff81000000 16M pmd 0xffffffff81000000-0xffffffff81800000 8M ro PSE GLB x pmd 0xffffffff81800000-0xffffffff819f3000 1996K ro GLB x pte 0xffffffff819f3000-0xffffffff81a00000 52K ro NX pte 0xffffffff81a00000-0xffffffff81e00000 4M ro PSE GLB NX pmd 0xffffffff81e00000-0xffffffff81e0b000 44K ro GLB NX pte 0xffffffff81e0b000-0xffffffff82000000 2004K ro NX pte 0xffffffff82000000-0xffffffff8214c000 1328K RW GLB NX pte 0xffffffff8214c000-0xffffffff8227e000 1224K RW NX pte 0xffffffff8227e000-0xffffffff82400000 1544K RW GLB NX pte 0xffffffff82400000-0xffffffff83200000 14M RW PSE GLB NX pmd 0xffffffff83200000-0xffffffffc0000000 974M pmd Based on work by PaX Team and Brad Spengler. Signed-off-by: Kees Cook Acked-by: Andy Lutomirski Acked-by: H. Peter Anvin Cc: Andy Lutomirski Cc: Arnd Bergmann Cc: Borislav Petkov Cc: Brad Spengler Cc: Brian Gerst Cc: David Brown Cc: Denys Vlasenko Cc: Emese Revfy Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Mathias Krause Cc: Michael Ellerman Cc: PaX Team Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: kernel-hardening@lists.openwall.com Cc: linux-arch Link: http://lkml.kernel.org/r/1455748879-21872-7-git-send-email-keescook@chromium.org Signed-off-by: Ingo Molnar --- diff --git a/arch/x86/entry/vdso/vdso2c.h b/arch/x86/entry/vdso/vdso2c.h index 0224987556ce..3f69326ed545 100644 --- a/arch/x86/entry/vdso/vdso2c.h +++ b/arch/x86/entry/vdso/vdso2c.h @@ -140,7 +140,7 @@ static void BITSFUNC(go)(void *raw_addr, size_t raw_len, fprintf(outfile, "#include \n"); fprintf(outfile, "\n"); fprintf(outfile, - "static unsigned char raw_data[%lu] __page_aligned_data = {", + "static unsigned char raw_data[%lu] __ro_after_init __aligned(PAGE_SIZE) = {", mapping_size); for (j = 0; j < stripped_len; j++) { if (j % 10 == 0)