From: Alexandre Ghiti <alex@xxxxxxxx> Subject: arm64, mm: make randomization selected by generic topdown mmap layout 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. Link: http://lkml.kernel.org/r/20190730055113.23635-6-alex@xxxxxxxx Signed-off-by: Alexandre Ghiti <alex@xxxxxxxx> Acked-by: Catalin Marinas <catalin.marinas@xxxxxxx> Acked-by: Kees Cook <keescook@xxxxxxxxxxxx> Reviewed-by: Christoph Hellwig <hch@xxxxxx> Reviewed-by: Luis Chamberlain <mcgrof@xxxxxxxxxx> Cc: Albert Ou <aou@xxxxxxxxxxxxxxxxx> Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx> Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx> Cc: James Hogan <jhogan@xxxxxxxxxx> Cc: Palmer Dabbelt <palmer@xxxxxxxxxx> Cc: Paul Burton <paul.burton@xxxxxxxx> Cc: Ralf Baechle <ralf@xxxxxxxxxxxxxx> Cc: Russell King <linux@xxxxxxxxxxxxxxx> Cc: Will Deacon <will.deacon@xxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- arch/Kconfig | 1 + arch/arm64/Kconfig | 1 - arch/arm64/kernel/process.c | 8 -------- mm/util.c | 11 +++++++++-- 4 files changed, 10 insertions(+), 11 deletions(-) --- a/arch/arm64/Kconfig~arm64-mm-make-randomization-selected-by-generic-topdown-mmap-layout +++ a/arch/arm64/Kconfig @@ -15,7 +15,6 @@ config ARM64 select ARCH_HAS_DMA_COHERENT_TO_PFN 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 --- a/arch/arm64/kernel/process.c~arm64-mm-make-randomization-selected-by-generic-topdown-mmap-layout +++ a/arch/arm64/kernel/process.c @@ -557,14 +557,6 @@ unsigned long arch_align_stack(unsigned 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. */ --- a/arch/Kconfig~arm64-mm-make-randomization-selected-by-generic-topdown-mmap-layout +++ a/arch/Kconfig @@ -715,6 +715,7 @@ 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 --- a/mm/util.c~arm64-mm-make-randomization-selected-by-generic-topdown-mmap-layout +++ a/mm/util.c @@ -321,7 +321,15 @@ unsigned long randomize_stack_top(unsign } #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; @@ -335,7 +343,6 @@ 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) { _
