On Sun, May 26, 2019 at 09:47:37AM -0400, Alexandre Ghiti wrote:
> This commits selects ARCH_HAS_ELF_RANDOMIZE when an arch uses the generic
> topdown mmap layout functions so that this security feature is on by
> default.
> Note that this commit also removes the possibility for arm64 to have elf
> randomization and no MMU: without MMU, the security added by randomization
> is worth nothing.
>
> Signed-off-by: Alexandre Ghiti <alex@xxxxxxxx>
Acked-by: Kees Cook <keescook@xxxxxxxxxxxx>
-Kees
> ---
> arch/Kconfig | 1 +
> arch/arm64/Kconfig | 1 -
> arch/arm64/kernel/process.c | 8 --------
> mm/util.c | 11 +++++++++--
> 4 files changed, 10 insertions(+), 11 deletions(-)
>
> diff --git a/arch/Kconfig b/arch/Kconfig
> index df3ab04270fa..3732654446cc 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -710,6 +710,7 @@ config HAVE_ARCH_COMPAT_MMAP_BASES
> config ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT
> bool
> depends on MMU
> + select ARCH_HAS_ELF_RANDOMIZE
>
> config HAVE_COPY_THREAD_TLS
> bool
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 3d754c19c11e..403bd3fffdbc 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -15,7 +15,6 @@ config ARM64
> select ARCH_HAS_DMA_MMAP_PGPROT
> select ARCH_HAS_DMA_PREP_COHERENT
> select ARCH_HAS_ACPI_TABLE_UPGRADE if ACPI
> - select ARCH_HAS_ELF_RANDOMIZE
> select ARCH_HAS_FAST_MULTIPLIER
> select ARCH_HAS_FORTIFY_SOURCE
> select ARCH_HAS_GCOV_PROFILE_ALL
> diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
> index 3767fb21a5b8..3f85f8f2d665 100644
> --- a/arch/arm64/kernel/process.c
> +++ b/arch/arm64/kernel/process.c
> @@ -535,14 +535,6 @@ unsigned long arch_align_stack(unsigned long sp)
> return sp & ~0xf;
> }
>
> -unsigned long arch_randomize_brk(struct mm_struct *mm)
> -{
> - if (is_compat_task())
> - return randomize_page(mm->brk, SZ_32M);
> - else
> - return randomize_page(mm->brk, SZ_1G);
> -}
> -
> /*
> * Called from setup_new_exec() after (COMPAT_)SET_PERSONALITY.
> */
> diff --git a/mm/util.c b/mm/util.c
> index 717f5d75c16e..8a38126edc74 100644
> --- a/mm/util.c
> +++ b/mm/util.c
> @@ -319,7 +319,15 @@ unsigned long randomize_stack_top(unsigned long stack_top)
> }
>
> #ifdef CONFIG_ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT
> -#ifdef CONFIG_ARCH_HAS_ELF_RANDOMIZE
> +unsigned long arch_randomize_brk(struct mm_struct *mm)
> +{
> + /* Is the current task 32bit ? */
> + if (!IS_ENABLED(CONFIG_64BIT) || is_compat_task())
> + return randomize_page(mm->brk, SZ_32M);
> +
> + return randomize_page(mm->brk, SZ_1G);
> +}
> +
> unsigned long arch_mmap_rnd(void)
> {
> unsigned long rnd;
> @@ -333,7 +341,6 @@ unsigned long arch_mmap_rnd(void)
>
> return rnd << PAGE_SHIFT;
> }
> -#endif /* CONFIG_ARCH_HAS_ELF_RANDOMIZE */
>
> static int mmap_is_legacy(struct rlimit *rlim_stack)
> {
> --
> 2.20.1
>
--
Kees Cook
