[OpenWrt-Devel] [PATCH] build: Activate ASLR PIE by default

[Felix Fietkau]

On 2019-02-13 23:15, Hauke Mehrtens wrote:
> This will build all executable as Position Independent Executables (PIE)
> by default. PIE executable can make full use of Address Space Layout
> Randomization (ASLR) because all sections can be placed at random
> offsets of the executed program. This makes it harder to exploit bugs
> in our binaries.
> 
> This will increase the size of executable, libraries are already build
> position independent and their size will not change.
> 
> This increases the size of the resulting images by about 3% on MIPS BE.
> I tested this with the default configuration for the lantiq xrx200
> target.
> 
> The size of the initramfs binaries increased by 2.88%:
> Without PIE:
> 5.303.716 openwrt-lantiq-xrx200-bt_homehub-v5a-initramfs-kernel.bin
> With PIE:
> 5.456.339 openwrt-lantiq-xrx200-bt_homehub-v5a-initramfs-kernel.bin
> 
> With PIE activated the executable are getting bigger, here are some
> examples from the lantiq mips_24kc target:
> 
> Without PIE:
> 112.309 /bin/opkg
> 299.061 /bin/busybox
> 456.549 /usr/sbin/wpad
> 
> With PIE:
> 142.496 /bin/opkg       (26.87% increase)
> 388.404 /bin/busybox    (29.87% increase)
> 580.128 /usr/sbin/wpad  (27.06% increase)
> 
> With PIE activated the sections of the binaries are loaded to
> different offsets for each program instance like shown here:
> 
> root at OpenWrt:/# cat /proc/self/maps
> 555c4000-55622000 r-xp 00000000 00:02 1030       /bin/busybox
> 55631000-55632000 r-xp 0005d000 00:02 1030       /bin/busybox
> 55632000-55633000 rwxp 0005e000 00:02 1030       /bin/busybox
> 55633000-55634000 rwxp 00000000 00:00 0
> 77ee2000-77f04000 r-xp 00000000 00:02 331        /lib/libgcc_s.so.1
> 77f04000-77f05000 r-xp 00012000 00:02 331        /lib/libgcc_s.so.1
> 77f05000-77f06000 rwxp 00013000 00:02 331        /lib/libgcc_s.so.1
> 77f06000-77f9a000 r-xp 00000000 00:02 329        /lib/libc.so
> 77fa9000-77fab000 rwxp 00093000 00:02 329        /lib/libc.so
> 77fab000-77fad000 rwxp 00000000 00:00 0
> 7fb26000-7fb47000 rw-p 00000000 00:00 0          [stack]
> 7fefb000-7fefc000 r-xp 00000000 00:00 0
> 7ff0a000-7ff0b000 r--p 00000000 00:00 0          [vvar]
> 7ff0b000-7ff0c000 r-xp 00000000 00:00 0          [vdso]
> root at OpenWrt:/# cat /proc/self/maps
> 5561d000-5567b000 r-xp 00000000 00:02 1030       /bin/busybox
> 5568a000-5568b000 r-xp 0005d000 00:02 1030       /bin/busybox
> 5568b000-5568c000 rwxp 0005e000 00:02 1030       /bin/busybox
> 5568c000-5568d000 rwxp 00000000 00:00 0
> 77e8e000-77eb0000 r-xp 00000000 00:02 331        /lib/libgcc_s.so.1
> 77eb0000-77eb1000 r-xp 00012000 00:02 331        /lib/libgcc_s.so.1
> 77eb1000-77eb2000 rwxp 00013000 00:02 331        /lib/libgcc_s.so.1
> 77eb2000-77f46000 r-xp 00000000 00:02 329        /lib/libc.so
> 77f55000-77f57000 rwxp 00093000 00:02 329        /lib/libc.so
> 77f57000-77f59000 rwxp 00000000 00:00 0
> 7fd1c000-7fd3d000 rw-p 00000000 00:00 0          [stack]
> 7fefb000-7fefc000 r-xp 00000000 00:00 0
> 7ff60000-7ff61000 r--p 00000000 00:00 0          [vvar]
> 7ff61000-7ff62000 r-xp 00000000 00:00 0          [vdso]
> root at OpenWrt:/#
> 
> Signed-off-by: Hauke Mehrtens <hauke at hauke-m.de>
> ---
> 
> I would like to get some comments if we should activate PIE by default.
> The advantage is that it will be harder to exploit OpenWrt, but on the 
> other hand the binaries are getting bigger. We could also restrict this 
> to some CPU types, but as targets share the binaries it is not really 
> possible to do this based on the target.
> 
> I am not sure if this should go into the next release or wait for later.
> 
> This could also break some packages, as it is possible to activate PIE 
> by default for some time many bugs are already fixed, but probably not 
> all of them.
I think this is a lot of extra bloat. Maybe we can add a restricted PIE
mode where packages can opt-in individually?

- Felix

_______________________________________________
openwrt-devel mailing list
openwrt-devel at lists.openwrt.org
https://lists.openwrt.org/mailman/listinfo/openwrt-devel