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

[Rosen Penev]

On Sat, Dec 22, 2018 at 1:14 PM Kevin 'ldir' Darbyshire-Bryant
<ldir at darbyshire-bryant.me.uk> wrote:
>
>
>
> > 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]
Hauke mentioned on IRC that CPU_MIPSR2 in the kernel's Kconfig enables
CPU_HAS_RIXI. grep the openwrt for RIXI to see what I mean.

HOWEVER, bcm47xx, ar71xx, ath79, mt7621, and a few others set
cpu_has_rixi to 0. This is significant as several CPUs in OpenWrt like
mt7620 should probably also be setting it if mt7621 is correct for
example.

This has to be bogus. I will definitely be run testing mt7621 device
to see if anything happens.
>
> 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
>
> Cheers,
>
> Kevin D-B
>
> 012C ACB2 28C6 C53E 9775  9123 B3A2 389B 9DE2 334A
>
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