On Wed, Apr 17, 2019 at 12:34 AM Alexandre Ghiti <alex@xxxxxxxx> wrote: > > In order to avoid wasting user address space by using bottom-up mmap > allocation scheme, prefer top-down scheme when possible. > > Before: > root@qemuriscv64:~# cat /proc/self/maps > 00010000-00016000 r-xp 00000000 fe:00 6389 /bin/cat.coreutils > 00016000-00017000 r--p 00005000 fe:00 6389 /bin/cat.coreutils > 00017000-00018000 rw-p 00006000 fe:00 6389 /bin/cat.coreutils > 00018000-00039000 rw-p 00000000 00:00 0 [heap] > 1555556000-155556d000 r-xp 00000000 fe:00 7193 /lib/ld-2.28.so > 155556d000-155556e000 r--p 00016000 fe:00 7193 /lib/ld-2.28.so > 155556e000-155556f000 rw-p 00017000 fe:00 7193 /lib/ld-2.28.so > 155556f000-1555570000 rw-p 00000000 00:00 0 > 1555570000-1555572000 r-xp 00000000 00:00 0 [vdso] > 1555574000-1555576000 rw-p 00000000 00:00 0 > 1555576000-1555674000 r-xp 00000000 fe:00 7187 /lib/libc-2.28.so > 1555674000-1555678000 r--p 000fd000 fe:00 7187 /lib/libc-2.28.so > 1555678000-155567a000 rw-p 00101000 fe:00 7187 /lib/libc-2.28.so > 155567a000-15556a0000 rw-p 00000000 00:00 0 > 3fffb90000-3fffbb1000 rw-p 00000000 00:00 0 [stack] > > After: > root@qemuriscv64:~# cat /proc/self/maps > 00010000-00016000 r-xp 00000000 fe:00 6389 /bin/cat.coreutils > 00016000-00017000 r--p 00005000 fe:00 6389 /bin/cat.coreutils > 00017000-00018000 rw-p 00006000 fe:00 6389 /bin/cat.coreutils > 00018000-00039000 rw-p 00000000 00:00 0 [heap] > 3ff7eb6000-3ff7ed8000 rw-p 00000000 00:00 0 > 3ff7ed8000-3ff7fd6000 r-xp 00000000 fe:00 7187 /lib/libc-2.28.so > 3ff7fd6000-3ff7fda000 r--p 000fd000 fe:00 7187 /lib/libc-2.28.so > 3ff7fda000-3ff7fdc000 rw-p 00101000 fe:00 7187 /lib/libc-2.28.so > 3ff7fdc000-3ff7fe2000 rw-p 00000000 00:00 0 > 3ff7fe4000-3ff7fe6000 r-xp 00000000 00:00 0 [vdso] > 3ff7fe6000-3ff7ffd000 r-xp 00000000 fe:00 7193 /lib/ld-2.28.so > 3ff7ffd000-3ff7ffe000 r--p 00016000 fe:00 7193 /lib/ld-2.28.so > 3ff7ffe000-3ff7fff000 rw-p 00017000 fe:00 7193 /lib/ld-2.28.so > 3ff7fff000-3ff8000000 rw-p 00000000 00:00 0 > 3fff888000-3fff8a9000 rw-p 00000000 00:00 0 [stack] > > Signed-off-by: Alexandre Ghiti <alex@xxxxxxxx> > Reviewed-by: Christoph Hellwig <hch@xxxxxx> Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx> -Kees > --- > arch/riscv/Kconfig | 11 +++++++++++ > 1 file changed, 11 insertions(+) > > diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig > index eb56c82d8aa1..f5897e0dbc1c 100644 > --- a/arch/riscv/Kconfig > +++ b/arch/riscv/Kconfig > @@ -49,6 +49,17 @@ config RISCV > select GENERIC_IRQ_MULTI_HANDLER > select ARCH_HAS_PTE_SPECIAL > select HAVE_EBPF_JIT if 64BIT > + select ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT if MMU > + select HAVE_ARCH_MMAP_RND_BITS > + > +config ARCH_MMAP_RND_BITS_MIN > + default 18 > + > +# max bits determined by the following formula: > +# VA_BITS - PAGE_SHIFT - 3 > +config ARCH_MMAP_RND_BITS_MAX > + default 33 if 64BIT # SV48 based > + default 18 > > config MMU > def_bool y > -- > 2.20.1 > -- Kees Cook
