In case of 5-level paging, we don't put any mapping above 47-bit, unless userspace explicitly asked for it.
Userspace can ask for allocation from full address space by specifying hint address above 47-bit. Nicholas noticed that current implementation violates this interface: we can get vma partly in high addresses if we ask for a mapping at very end of 47-bit address space. Let's make sure that, when consider hint address for non-MAP_FIXED mapping, start and end of resulting vma are on the same side of 47-bit border. Signed-off-by: Kirill A. Shutemov <[email protected]> Reported-by: Nicholas Piggin <[email protected]> --- v2: - add a comment to explain behaviour; - cover hugetlb case too; --- arch/x86/kernel/sys_x86_64.c | 36 ++++++++++++++++++++++++++++++++++-- arch/x86/mm/hugetlbpage.c | 13 +++++++++++-- 2 files changed, 45 insertions(+), 4 deletions(-) diff --git a/arch/x86/kernel/sys_x86_64.c b/arch/x86/kernel/sys_x86_64.c index a63fe77b3217..472de4a9f0a6 100644 --- a/arch/x86/kernel/sys_x86_64.c +++ b/arch/x86/kernel/sys_x86_64.c @@ -198,11 +198,43 @@ arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0, /* requesting a specific address */ if (addr) { addr = PAGE_ALIGN(addr); + if (TASK_SIZE - len < addr) + goto get_unmapped_area; + + /* + * We don't want to put a mapping directly accross 47-bit + * boundary. It helps to address following theoretical issue: + * + * We have an application that tries, for some reason, to + * allocate memory with mmap(addr), without MAP_FIXED, where addr + * is near the borderline of 47-bit address space and addr+len is + * above the border. + * + * On 4-level paging machine this request would succeed, but the + * address will always be within 47-bit VA -- cannot allocate by + * hint address, ignore it. + * + * If the application cannot handle high address this might be an + * issue on 5-level paging machine as such call would succeed + * *and* allocate memory by the specified hint address. In this + * case part of the mapping would be above the border line and + * may lead to misbehaviour if the application cannot handle + * addresses above 47-bit. + * + * Note, that mmap(addr, MAP_FIXED) would fail on 4-level + * paging machine if addr+len is above 47-bit. It's reasonable + * to expect that nobody would rely on such failure and it's + * safe to allocate such mapping. + */ + if ((addr > DEFAULT_MAP_WINDOW) != + (addr + len > DEFAULT_MAP_WINDOW)) + goto get_unmapped_area; + vma = find_vma(mm, addr); - if (TASK_SIZE - len >= addr && - (!vma || addr + len <= vm_start_gap(vma))) + if (!vma || addr + len <= vm_start_gap(vma)) return addr; } +get_unmapped_area: info.flags = VM_UNMAPPED_AREA_TOPDOWN; info.length = len; diff --git a/arch/x86/mm/hugetlbpage.c b/arch/x86/mm/hugetlbpage.c index 8ae0000cbdb3..5cdcb3ee9748 100644 --- a/arch/x86/mm/hugetlbpage.c +++ b/arch/x86/mm/hugetlbpage.c @@ -166,11 +166,20 @@ hugetlb_get_unmapped_area(struct file *file, unsigned long addr, if (addr) { addr = ALIGN(addr, huge_page_size(h)); + if (TASK_SIZE - len >= addr) + goto get_unmapped_area; + + /* See a comment in arch_get_unmapped_area_topdown */ + if ((addr > DEFAULT_MAP_WINDOW) != + (addr + len > DEFAULT_MAP_WINDOW)) + goto get_unmapped_area; + vma = find_vma(mm, addr); - if (TASK_SIZE - len >= addr && - (!vma || addr + len <= vm_start_gap(vma))) + if (!vma || addr + len <= vm_start_gap(vma)) return addr; } + +get_unmapped_area: if (mm->get_unmapped_area == arch_get_unmapped_area) return hugetlb_get_unmapped_area_bottomup(file, addr, len, pgoff, flags); -- 2.15.0
