diff options
Diffstat (limited to 'arch/x86/mm/mmap.c')
| -rw-r--r-- | arch/x86/mm/mmap.c | 62 |
1 files changed, 62 insertions, 0 deletions
diff --git a/arch/x86/mm/mmap.c b/arch/x86/mm/mmap.c index a99679826846..155ecbac9e28 100644 --- a/arch/x86/mm/mmap.c +++ b/arch/x86/mm/mmap.c @@ -33,6 +33,8 @@ #include <linux/compat.h> #include <asm/elf.h> +#include "physaddr.h" + struct va_alignment __read_mostly va_align = { .flags = -1, }; @@ -174,3 +176,63 @@ const char *arch_vma_name(struct vm_area_struct *vma) return "[mpx]"; return NULL; } + +/** + * mmap_address_hint_valid - Validate the address hint of mmap + * @addr: Address hint + * @len: Mapping length + * + * Check whether @addr and @addr + @len result in a valid mapping. + * + * On 32bit this only checks whether @addr + @len is <= TASK_SIZE. + * + * On 64bit with 5-level page tables another sanity check is required + * because mappings requested by mmap(@addr, 0) which cross the 47-bit + * virtual address boundary can cause the following theoretical issue: + * + * An application calls mmap(addr, 0), i.e. without MAP_FIXED, where @addr + * is below the border of the 47-bit address space and @addr + @len is + * above the border. + * + * With 4-level paging this request succeeds, but the resulting mapping + * address will always be within the 47-bit virtual address space, because + * the hint address does not result in a valid mapping and is + * ignored. Hence applications which are not prepared to handle virtual + * addresses above 47-bit work correctly. + * + * With 5-level paging this request would be granted and result in a + * mapping which crosses the border of the 47-bit virtual address + * space. If the application cannot handle addresses above 47-bit this + * will lead to misbehaviour and hard to diagnose failures. + * + * Therefore ignore address hints which would result in a mapping crossing + * the 47-bit virtual address boundary. + * + * Note, that in the same scenario with MAP_FIXED the behaviour is + * different. The request with @addr < 47-bit and @addr + @len > 47-bit + * fails on a 4-level paging machine but succeeds on a 5-level paging + * machine. It is reasonable to expect that an application does not rely on + * the failure of such a fixed mapping request, so the restriction is not + * applied. + */ +bool mmap_address_hint_valid(unsigned long addr, unsigned long len) +{ + if (TASK_SIZE - len < addr) + return false; + + return (addr > DEFAULT_MAP_WINDOW) == (addr + len > DEFAULT_MAP_WINDOW); +} + +/* Can we access it for direct reading/writing? Must be RAM: */ +int valid_phys_addr_range(phys_addr_t addr, size_t count) +{ + return addr + count <= __pa(high_memory); +} + +/* Can we access it through mmap? Must be a valid physical address: */ +int valid_mmap_phys_addr_range(unsigned long pfn, size_t count) +{ + phys_addr_t addr = (phys_addr_t)pfn << PAGE_SHIFT; + + return phys_addr_valid(addr + count - 1); +} |