This patchset reduces the size of the user-accessible address space for compat tasks by a page. Currently, compat tasks running on arm64 can allocate memory up to TASK_SIZE_32 (UL(0x100000000)). This means that mmap() allocations, if we treat them as returning an array, are not compliant with the sections 6.5.8 of the C standard (C99) which states that: "If the expression P points to an element of an array object and the expression Q points to the last element of the same array object, the pointer expression Q+1 compares greater than P". A solution to this problem is to reduce TASK_SIZE_32 of a page. But, in the current implementation, compat installs a special page called "[vectors]" that contains sigreturn trampolines and kuser helpers, and this is done at fixed address specified by the kuser helpers ABI (0xffff0000) which overlaps with the last page when 64K pages are enabled. This patchset address the issue creating separate pages for vectors and sigpage in a similar way to what happens today on arm and disabling kuser helpers when 64K pages are enabled. Cc: Catalin Marinas <catalin.marinas@xxxxxxx> Cc: Will Deacon <will.deacon@xxxxxxx> Cc: Jann Horn <jannh@xxxxxxxxxx> Cc: Mark Rutland <mark.rutland@xxxxxxx> Signed-off-by: Vincenzo Frascino <vincenzo.frascino@xxxxxxx> Vincenzo Frascino (5): arm64: compat: Alloc separate pages for vectors and sigpage arm64: compat: Split kuser32 arm64: compat: Refactor aarch32_alloc_vdso_pages() arm64: compat: Add KUSER_HELPERS config option arm64: compat: Reduce address limit arch/arm64/Kconfig | 31 ++++++ arch/arm64/include/asm/elf.h | 6 +- arch/arm64/include/asm/processor.h | 6 +- arch/arm64/include/asm/signal32.h | 2 - arch/arm64/kernel/Makefile | 5 +- arch/arm64/kernel/kuser32.S | 65 +------------ arch/arm64/kernel/signal32.c | 5 +- arch/arm64/kernel/sigreturn32.S | 46 +++++++++ arch/arm64/kernel/vdso.c | 150 +++++++++++++++++++++++------ 9 files changed, 213 insertions(+), 103 deletions(-) create mode 100644 arch/arm64/kernel/sigreturn32.S -- 2.21.0
