On Fri, Sep 25, 2015 at 12:22 AM, Ingo Molnar <[email protected]> wrote: > > * Kees Cook <[email protected]> wrote: > >> On Thu, Sep 24, 2015 at 1:26 PM, Stephen Smalley <[email protected]> wrote: >> > Hi, >> > >> > With the attached config and 4.3-rc2 on x86_64, I see the following in >> > /sys/kernel/debug/kernel_page_tables: >> > ... >> > ---[ High Kernel Mapping ]--- >> > 0xffffffff80000000-0xffffffff81000000 16M >> > pmd >> > 0xffffffff81000000-0xffffffff81600000 6M ro PSE >> > GLB x pmd >> > 0xffffffff81600000-0xffffffff81775000 1492K ro >> > GLB x pte >> > 0xffffffff81775000-0xffffffff81800000 556K RW >> > GLB x pte >> > ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ >> > 0xffffffff81800000-0xffffffff81a00000 2M ro PSE >> > GLB NX pmd >> > 0xffffffff81a00000-0xffffffff81b43000 1292K ro >> > GLB NX pte >> > 0xffffffff81b43000-0xffffffff82000000 4852K RW >> > GLB NX pte >> > 0xffffffff82000000-0xffffffff82200000 2M RW PSE >> > GLB NX pmd >> > 0xffffffff82200000-0xffffffffa0000000 478M >> > pmd >> > ... >> > >> > This region seems to be between the end of ex_table and the start of >> > rodata, >> > $ objdump -x vmlinux | sort >> > ... >> > ffffffff817728b0 g __ex_table 0000000000000000 __start___ex_table >> > ffffffff817728b0 l d __ex_table 0000000000000000 __ex_table >> > ffffffff81774998 g __ex_table 0000000000000000 __stop___ex_table >> > ffffffff81800000 g .rodata 0000000000000000 __start_rodata >> > ffffffff81800000 l d .rodata 0000000000000000 .rodata >> > ... >> > >> > $ readelf -a vmlinux >> > ... >> > Section Headers: >> > [Nr] Name Type Address Offset >> > Size EntSize Flags Link Info Align >> > ... >> > [ 3] __ex_table PROGBITS ffffffff817728b0 009728b0 >> > 00000000000020e8 0000000000000000 A 0 0 8 >> > [ 4] .rodata PROGBITS ffffffff81800000 00a00000 >> > 00000000002eefd2 0000000000000000 A 0 0 64 >> > ... >> > >> > I see a similar rwx mapping with the stock Fedora kernels (e.g. 4.1.6), so >> > it isn't new to 4.3. >> >> To me it looks like another alignment/padding issue like got fixed >> before. The space between __ex_table and rodata is (seems?) unused, so >> the default page table permissions end up being W+X. Can we fix the >> default to be NX instead? It'll make these bugs stay gone. > > Yeah. Wanna send a patch for that?
I haven't found where that is actually happening. :( If anyone has pointers, I can dig a bit more. -Kees -- Kees Cook Chrome OS Security -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
