Bhupesh Sharma <[email protected]> writes: > powerpc arch_mmap_rnd() currently uses hard-coded values - (23-PAGE_SHIFT) for > 32-bit and (30-PAGE_SHIFT) for 64-bit, to generate the random offset > for the mmap base address for a ASLR ELF. > > This patch makes sure that powerpc mmap arch_mmap_rnd() implementation > is similar to other ARCHs (like x86, arm64) and uses mmap_rnd_bits > and helpers to generate the mmap address randomization. > > The maximum and minimum randomization range values represent > a compromise between increased ASLR effectiveness and avoiding > address-space fragmentation. > > Using the Kconfig option and suitable /proc tunable, platform > developers may choose where to place this compromise. > > Also this patch keeps the default values as new minimums. > > Signed-off-by: Bhupesh Sharma <[email protected]> > Reviewed-by: Kees Cook <[email protected]> > --- > * Changes since v2: > v2 can be seen here (https://patchwork.kernel.org/patch/9551509/) > - Changed a few minimum and maximum randomization ranges as per Michael's > suggestion. > - Corrected Kees's email address in the Reviewed-by line. > - Added further comments in kconfig to explain how the address ranges > were worked out. > > * Changes since v1: > v1 can be seen here > (https://lists.ozlabs.org/pipermail/linuxppc-dev/2017-February/153594.html) > - No functional change in this patch. > - Dropped PATCH 2/2 from v1 as recommended by Kees Cook. > > arch/powerpc/Kconfig | 44 ++++++++++++++++++++++++++++++++++++++++++++ > arch/powerpc/mm/mmap.c | 7 ++++--- > 2 files changed, 48 insertions(+), 3 deletions(-) > > diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig > index 97a8bc8..84aae67 100644 > --- a/arch/powerpc/Kconfig > +++ b/arch/powerpc/Kconfig > @@ -22,6 +22,48 @@ config MMU > bool > default y > > +# min bits determined by the following formula: > +# VA_BITS - PAGE_SHIFT - CONSTANT > +# where, > +# VA_BITS = 46 bits for 64BIT and 4GB - 1 Page = 31 bits for 32BIT
Where did we derive that 46 bits from ? is that based on TASK_SIZE ? > +# CONSTANT = 16 for 64BIT and 8 for 32BIT > +config ARCH_MMAP_RND_BITS_MIN > + default 5 if PPC_256K_PAGES && 32BIT # 31 - 18 - 8 = 5 > + default 7 if PPC_64K_PAGES && 32BIT # 31 - 16 - 8 = 7 > + default 9 if PPC_16K_PAGES && 32BIT # 31 - 14 - 8 = 9 > + default 11 if PPC_4K_PAGES && 32BIT # 31 - 12 - 8 = 11 > + default 12 if PPC_256K_PAGES && 64BIT # 46 - 18 - 16 = 12 > + default 14 if PPC_64K_PAGES && 64BIT # 46 - 16 - 16 = 14 > + default 16 if PPC_16K_PAGES && 64BIT # 46 - 14 - 16 = 16 > + default 18 if PPC_4K_PAGES && 64BIT # 46 - 12 - 16 = 18 > + > +# max bits determined by the following formula: -aneesh
