On Fri, Feb 17, 2017 at 6:13 AM, Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> wrote: > This patch introduces two new prctl(2) handles to manage maximum virtual > address available to userspace to map. > > On x86, 5-level paging enables 56-bit userspace virtual address space. > Not all user space is ready to handle wide addresses. It's known that > at least some JIT compilers use higher bits in pointers to encode their > information. It collides with valid pointers with 5-level paging and > leads to crashes. > > The patch aims to address this compatibility issue. > > MM would use the address as upper limit of virtual address available to > map by userspace, instead of TASK_SIZE. > > The limit will be equal to TASK_SIZE everywhere, but the machine > with 5-level paging enabled. In this case, the default limit would be > (1UL << 47) - PAGE_SIZE. It’s current x86-64 TASK_SIZE_MAX with 4-level > paging which known to be safe. I think this patch need to be split up. In particular, the addition and use of mmap_max_addr() should be its own patch that doesn't change any semantics. > diff --git a/arch/x86/include/asm/mmu_context.h b/arch/x86/include/asm/mmu_context.h > index 306c7e12af55..50bdfd6ab866 100644 > --- a/arch/x86/include/asm/mmu_context.h > +++ b/arch/x86/include/asm/mmu_context.h > @@ -117,6 +117,7 @@ static inline int init_new_context(struct task_struct *tsk, > } > #endif > init_new_context_ldt(tsk, mm); > + mm->context.max_vaddr = MAX_VADDR_DEFAULT; Is this actually correct for 32-bit binaries? Although, given the stuff Dmitry is working on, it might pay to separately track the 32-bit and 64-bit limits per mm. If you haven't been following it, Dmitry is trying to fix a bug in which an explicit 32-bit syscall (int80 or similar) in an otherwise 64-bit process can allocate a VMA above 4GB that gets truncated. Also, why the macro? Why not just put the number in here? > -#define TASK_SIZE_MAX ((1UL << 47) - PAGE_SIZE) > +#define TASK_SIZE_MAX ((1UL << __VIRTUAL_MASK_SHIFT) - PAGE_SIZE) This should be in the > -#define STACK_TOP TASK_SIZE > +#define STACK_TOP mmap_max_addr() Off the top of my head, this looks wrong. The 32-bit check got lost, I think. > +unsigned long set_max_vaddr(unsigned long addr) > +{ Perhaps this function could set a different field depending on is_compat_syscall(). Anyway, can you and Dmitry try to reconcile your patches? -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html