As covered in the commit log for c44357c2e76b ("x86/mm: care about shadow stack guard gap during placement") our current mmap() implementation does not take care to ensure that a new mapping isn't placed with existing mappings inside it's own guard gaps. This is particularly important for shadow stacks since if two shadow stacks end up getting placed adjacent to each other then they can overflow into each other which weakens the protection offered by the feature.
On x86 there is a custom arch_get_unmapped_area() which was updated by the above commit to cover this case by specifying a start_gap for allocations with VM_SHADOW_STACK. Both arm64 and RISC-V have equivalent features and use the generic implementation of arch_get_unmapped_area() so let's make the equivalent change there so they also don't get shadow stack pages placed without guard pages. The arm64 and RISC-V shadow stack implementations are currently on the list: https://lore.kernel.org/r/20240829-arm64-gcs-v12-0-42fec94743 https://lore.kernel.org/lkml/20240403234054.2020347-1-de...@rivosinc.com/ Given the addition of the use of vm_flags in the generic implementation we also simplify the set of possibilities that have to be dealt with in the core code by making arch_get_unmapped_area() take vm_flags as standard. This is a bit invasive since the prototype change touches quite a few architectures but since the parameter is ignored the change is straightforward, the simplification for the generic code seems worth it. Changes in v2: - Add comment to stack_guard_placement() - Build fixes for xtensa and MIPS. - Link to v1: https://lore.kernel.org/r/20240902-mm-generic-shadow-stack-guard-v1-0-9acda38b3...@kernel.org --- Mark Brown (3): mm: Make arch_get_unmapped_area() take vm_flags by default mm: Pass vm_flags to generic_get_unmapped_area() mm: Care about shadow stack guard gap when getting an unmapped area arch/alpha/kernel/osf_sys.c | 2 +- arch/arc/mm/mmap.c | 3 ++- arch/arm/mm/mmap.c | 7 ++--- arch/csky/abiv1/mmap.c | 3 ++- arch/loongarch/mm/mmap.c | 5 ++-- arch/mips/mm/mmap.c | 5 ++-- arch/parisc/kernel/sys_parisc.c | 5 ++-- arch/parisc/mm/hugetlbpage.c | 2 +- arch/powerpc/mm/book3s64/slice.c | 10 ++++--- arch/s390/mm/mmap.c | 4 +-- arch/sh/mm/mmap.c | 5 ++-- arch/sparc/kernel/sys_sparc_32.c | 2 +- arch/sparc/kernel/sys_sparc_64.c | 4 +-- arch/x86/include/asm/pgtable_64.h | 1 - arch/x86/kernel/sys_x86_64.c | 21 +++------------ arch/xtensa/kernel/syscall.c | 3 ++- include/linux/sched/mm.h | 27 +++++++------------ mm/mmap.c | 55 +++++++++++++++++++-------------------- 18 files changed, 75 insertions(+), 89 deletions(-) --- base-commit: 7c626ce4bae1ac14f60076d00eafe71af30450ba change-id: 20240830-mm-generic-shadow-stack-guard-5bc5b8d0e95d Best regards, -- Mark Brown <broo...@kernel.org> _______________________________________________ linux-snps-arc mailing list linux-snps-arc@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-snps-arc