Message ID | 1447886901-26098-5-git-send-email-dcashman@android.com (mailing list archive) |
---|---|
State | New, archived |
Headers | show |
On Wed, Nov 18, 2015 at 2:48 PM, Daniel Cashman <dcashman@android.com> wrote: > From: dcashman <dcashman@google.com> > > x86: arch_mmap_rnd() uses hard-coded values, 8 for 32-bit and 28 for > 64-bit, to generate the random offset for the mmap base address. > This value represents a compromise between increased ASLR > effectiveness and avoiding address-space fragmentation. Replace it > with a Kconfig option, which is sensibly bounded, so that platform > developers may choose where to place this compromise. Keep default > values as new minimums. > > Signed-off-by: Daniel Cashman <dcashman@google.com> > --- > arch/x86/Kconfig | 16 ++++++++++++++++ > arch/x86/mm/mmap.c | 12 ++++++------ > 2 files changed, 22 insertions(+), 6 deletions(-) > > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig > index db3622f..12768c4 100644 > --- a/arch/x86/Kconfig > +++ b/arch/x86/Kconfig > @@ -82,6 +82,8 @@ config X86 > select HAVE_ARCH_KASAN if X86_64 && SPARSEMEM_VMEMMAP > select HAVE_ARCH_KGDB > select HAVE_ARCH_KMEMCHECK > + select HAVE_ARCH_MMAP_RND_BITS > + select HAVE_ARCH_MMAP_RND_COMPAT_BITS if COMPAT > select HAVE_ARCH_SECCOMP_FILTER > select HAVE_ARCH_SOFT_DIRTY if X86_64 > select HAVE_ARCH_TRACEHOOK > @@ -183,6 +185,20 @@ config HAVE_LATENCYTOP_SUPPORT > config MMU > def_bool y > > +config ARCH_MMAP_RND_BITS_MIN > + default 28 if 64BIT > + default 8 > + > +config ARCH_MMAP_RND_BITS_MAX > + default 32 if 64BIT > + default 16 > + > +config ARCH_MMAP_RND_COMPAT_BITS_MIN > + default 8 > + > +config ARCH_MMAP_RND_COMPAT_BITS_MAX > + default 16 > + > config SBUS > bool > > diff --git a/arch/x86/mm/mmap.c b/arch/x86/mm/mmap.c > index 844b06d..647fecf 100644 > --- a/arch/x86/mm/mmap.c > +++ b/arch/x86/mm/mmap.c > @@ -69,14 +69,14 @@ unsigned long arch_mmap_rnd(void) > { > unsigned long rnd; > > - /* > - * 8 bits of randomness in 32bit mmaps, 20 address space bits > - * 28 bits of randomness in 64bit mmaps, 40 address space bits > - */ > if (mmap_is_ia32()) > - rnd = (unsigned long)get_random_int() % (1<<8); > +#ifdef CONFIG_COMPAT > + rnd = (unsigned long)get_random_int() % (1 << mmap_rnd_compat_bits); > +#else > + rnd = (unsigned long)get_random_int() % (1 << mmap_rnd_bits); > +#endif Oh, that is a weird side-effect of x86's compat: a 32-bit build isn't compat, so it needs the native bits. I'm trying to resist bikeshedding the names again, so probably this should stay as-is. -Kees > else > - rnd = (unsigned long)get_random_int() % (1<<28); > + rnd = (unsigned long)get_random_int() % (1 << mmap_rnd_bits); > > return rnd << PAGE_SHIFT; > } > -- > 2.6.0.rc2.230.g3dd15c0 >
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index db3622f..12768c4 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -82,6 +82,8 @@ config X86 select HAVE_ARCH_KASAN if X86_64 && SPARSEMEM_VMEMMAP select HAVE_ARCH_KGDB select HAVE_ARCH_KMEMCHECK + select HAVE_ARCH_MMAP_RND_BITS + select HAVE_ARCH_MMAP_RND_COMPAT_BITS if COMPAT select HAVE_ARCH_SECCOMP_FILTER select HAVE_ARCH_SOFT_DIRTY if X86_64 select HAVE_ARCH_TRACEHOOK @@ -183,6 +185,20 @@ config HAVE_LATENCYTOP_SUPPORT config MMU def_bool y +config ARCH_MMAP_RND_BITS_MIN + default 28 if 64BIT + default 8 + +config ARCH_MMAP_RND_BITS_MAX + default 32 if 64BIT + default 16 + +config ARCH_MMAP_RND_COMPAT_BITS_MIN + default 8 + +config ARCH_MMAP_RND_COMPAT_BITS_MAX + default 16 + config SBUS bool diff --git a/arch/x86/mm/mmap.c b/arch/x86/mm/mmap.c index 844b06d..647fecf 100644 --- a/arch/x86/mm/mmap.c +++ b/arch/x86/mm/mmap.c @@ -69,14 +69,14 @@ unsigned long arch_mmap_rnd(void) { unsigned long rnd; - /* - * 8 bits of randomness in 32bit mmaps, 20 address space bits - * 28 bits of randomness in 64bit mmaps, 40 address space bits - */ if (mmap_is_ia32()) - rnd = (unsigned long)get_random_int() % (1<<8); +#ifdef CONFIG_COMPAT + rnd = (unsigned long)get_random_int() % (1 << mmap_rnd_compat_bits); +#else + rnd = (unsigned long)get_random_int() % (1 << mmap_rnd_bits); +#endif else - rnd = (unsigned long)get_random_int() % (1<<28); + rnd = (unsigned long)get_random_int() % (1 << mmap_rnd_bits); return rnd << PAGE_SHIFT; }