On Wed, Dec 9, 2015 at 1:43 PM, Kees Cook <keescook@xxxxxxxxxxxx> wrote: > 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 <keescook@xxxxxxxxxxxx> Acked-by: Andy Lutomirski <luto@xxxxxxxxxx> --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
