[OpenWrt-Devel] [PATCH] kernel: MIPS: math-emu Write-protect delay slot emulation pages

Kevin 'ldir' Darbyshire-Bryant ldir at darbyshire-bryant.me.uk
Sat Dec 22 16:14:12 EST 2018

> On 22 Dec 2018, at 18:28, Hauke Mehrtens <hauke at hauke-m.de> wrote:
> Hi Yousong,
> ASLR is currently not activated by default in OpenWrt, so the binary itself is not randomized. Activate CONFIG_PKG_ASLR_PIE to compile Openwrt with ASLR, but this increases the size of the binary.
> I haven't understood why some parts of the busybox binary and other binaries are mapped rwx, when I look into it with readelf no section is mapped rwx, but it looks like some sections are ending at an not page aligned offset and the next section starts directly after that. I assume that Linux merges the permissions when one page needs different permissions.
> I am still not sure if the common mips CPUs (24Kec, 74Kec) support restricting execution on pages anyway.
> Huake

At the risk of going further down the rabbit hole/off topic, if you set the cpu_has_rixi to 1 in  target/linux/ath79/patches-4.14/0014-MIPS-ath79-finetune-cpu-overrides.patch and with PKG_ASLR_PIE [=y]

you get:
cat /proc/self/maps 
00400000-0047a000 r-xp 00000000 1f:03 1825       /bin/busybox
00489000-0048a000 r--p 00079000 1f:03 1825       /bin/busybox
0048a000-0048b000 rw-p 0007a000 1f:03 1825       /bin/busybox
77e38000-77e5d000 r-xp 00000000 1f:03 2298       /lib/libgcc_s.so.1
77e5d000-77e5e000 rw-p 00015000 1f:03 2298       /lib/libgcc_s.so.1
77e5e000-77ef1000 r-xp 00000000 1f:03 2474       /lib/libc.so
77f00000-77f02000 rw-p 00092000 1f:03 2474       /lib/libc.so
77f02000-77f04000 rw-p 00000000 00:00 0 
7f9bd000-7f9de000 rw-p 00000000 00:00 0          [stack]
7fefb000-7fefc000 r-xp 00000000 00:00 0 
7ff68000-7ff69000 r--p 00000000 00:00 0          [vvar]
7ff69000-7ff6a000 r-xp 00000000 00:00 0          [vdso]

The archer hasn’t blown up…….yet


Kevin D-B

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