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https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
synced 2024-08-27 19:29:37 +00:00
![Linus Torvalds](/assets/img/avatar_default.png)
Pull x86 protection key support from Ingo Molnar: "This tree adds support for a new memory protection hardware feature that is available in upcoming Intel CPUs: 'protection keys' (pkeys). There's a background article at LWN.net: https://lwn.net/Articles/643797/ The gist is that protection keys allow the encoding of user-controllable permission masks in the pte. So instead of having a fixed protection mask in the pte (which needs a system call to change and works on a per page basis), the user can map a (handful of) protection mask variants and can change the masks runtime relatively cheaply, without having to change every single page in the affected virtual memory range. This allows the dynamic switching of the protection bits of large amounts of virtual memory, via user-space instructions. It also allows more precise control of MMU permission bits: for example the executable bit is separate from the read bit (see more about that below). This tree adds the MM infrastructure and low level x86 glue needed for that, plus it adds a high level API to make use of protection keys - if a user-space application calls: mmap(..., PROT_EXEC); or mprotect(ptr, sz, PROT_EXEC); (note PROT_EXEC-only, without PROT_READ/WRITE), the kernel will notice this special case, and will set a special protection key on this memory range. It also sets the appropriate bits in the Protection Keys User Rights (PKRU) register so that the memory becomes unreadable and unwritable. So using protection keys the kernel is able to implement 'true' PROT_EXEC on x86 CPUs: without protection keys PROT_EXEC implies PROT_READ as well. Unreadable executable mappings have security advantages: they cannot be read via information leaks to figure out ASLR details, nor can they be scanned for ROP gadgets - and they cannot be used by exploits for data purposes either. We know about no user-space code that relies on pure PROT_EXEC mappings today, but binary loaders could start making use of this new feature to map binaries and libraries in a more secure fashion. There is other pending pkeys work that offers more high level system call APIs to manage protection keys - but those are not part of this pull request. Right now there's a Kconfig that controls this feature (CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS) that is default enabled (like most x86 CPU feature enablement code that has no runtime overhead), but it's not user-configurable at the moment. If there's any serious problem with this then we can make it configurable and/or flip the default" * 'mm-pkeys-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (38 commits) x86/mm/pkeys: Fix mismerge of protection keys CPUID bits mm/pkeys: Fix siginfo ABI breakage caused by new u64 field x86/mm/pkeys: Fix access_error() denial of writes to write-only VMA mm/core, x86/mm/pkeys: Add execute-only protection keys support x86/mm/pkeys: Create an x86 arch_calc_vm_prot_bits() for VMA flags x86/mm/pkeys: Allow kernel to modify user pkey rights register x86/fpu: Allow setting of XSAVE state x86/mm: Factor out LDT init from context init mm/core, x86/mm/pkeys: Add arch_validate_pkey() mm/core, arch, powerpc: Pass a protection key in to calc_vm_flag_bits() x86/mm/pkeys: Actually enable Memory Protection Keys in the CPU x86/mm/pkeys: Add Kconfig prompt to existing config option x86/mm/pkeys: Dump pkey from VMA in /proc/pid/smaps x86/mm/pkeys: Dump PKRU with other kernel registers mm/core, x86/mm/pkeys: Differentiate instruction fetches x86/mm/pkeys: Optimize fault handling in access_error() mm/core: Do not enforce PKEY permissions on remote mm access um, pkeys: Add UML arch_*_access_permitted() methods mm/gup, x86/mm/pkeys: Check VMAs and PTEs for protection keys x86/mm/gup: Simplify get_user_pages() PTE bit handling ...
450 lines
11 KiB
C
450 lines
11 KiB
C
/*
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* Lockless get_user_pages_fast for x86
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*
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* Copyright (C) 2008 Nick Piggin
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* Copyright (C) 2008 Novell Inc.
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*/
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#include <linux/sched.h>
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#include <linux/mm.h>
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#include <linux/vmstat.h>
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#include <linux/highmem.h>
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#include <linux/swap.h>
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#include <linux/memremap.h>
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#include <asm/mmu_context.h>
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#include <asm/pgtable.h>
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static inline pte_t gup_get_pte(pte_t *ptep)
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{
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#ifndef CONFIG_X86_PAE
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return READ_ONCE(*ptep);
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#else
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/*
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* With get_user_pages_fast, we walk down the pagetables without taking
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* any locks. For this we would like to load the pointers atomically,
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* but that is not possible (without expensive cmpxchg8b) on PAE. What
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* we do have is the guarantee that a pte will only either go from not
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* present to present, or present to not present or both -- it will not
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* switch to a completely different present page without a TLB flush in
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* between; something that we are blocking by holding interrupts off.
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*
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* Setting ptes from not present to present goes:
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* ptep->pte_high = h;
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* smp_wmb();
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* ptep->pte_low = l;
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*
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* And present to not present goes:
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* ptep->pte_low = 0;
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* smp_wmb();
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* ptep->pte_high = 0;
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*
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* We must ensure here that the load of pte_low sees l iff pte_high
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* sees h. We load pte_high *after* loading pte_low, which ensures we
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* don't see an older value of pte_high. *Then* we recheck pte_low,
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* which ensures that we haven't picked up a changed pte high. We might
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* have got rubbish values from pte_low and pte_high, but we are
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* guaranteed that pte_low will not have the present bit set *unless*
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* it is 'l'. And get_user_pages_fast only operates on present ptes, so
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* we're safe.
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*
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* gup_get_pte should not be used or copied outside gup.c without being
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* very careful -- it does not atomically load the pte or anything that
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* is likely to be useful for you.
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*/
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pte_t pte;
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retry:
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pte.pte_low = ptep->pte_low;
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smp_rmb();
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pte.pte_high = ptep->pte_high;
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smp_rmb();
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if (unlikely(pte.pte_low != ptep->pte_low))
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goto retry;
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return pte;
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#endif
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}
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static void undo_dev_pagemap(int *nr, int nr_start, struct page **pages)
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{
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while ((*nr) - nr_start) {
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struct page *page = pages[--(*nr)];
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ClearPageReferenced(page);
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put_page(page);
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}
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}
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/*
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* 'pteval' can come from a pte, pmd or pud. We only check
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* _PAGE_PRESENT, _PAGE_USER, and _PAGE_RW in here which are the
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* same value on all 3 types.
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*/
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static inline int pte_allows_gup(unsigned long pteval, int write)
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{
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unsigned long need_pte_bits = _PAGE_PRESENT|_PAGE_USER;
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if (write)
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need_pte_bits |= _PAGE_RW;
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if ((pteval & need_pte_bits) != need_pte_bits)
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return 0;
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/* Check memory protection keys permissions. */
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if (!__pkru_allows_pkey(pte_flags_pkey(pteval), write))
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return 0;
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return 1;
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}
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/*
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* The performance critical leaf functions are made noinline otherwise gcc
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* inlines everything into a single function which results in too much
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* register pressure.
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*/
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static noinline int gup_pte_range(pmd_t pmd, unsigned long addr,
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unsigned long end, int write, struct page **pages, int *nr)
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{
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struct dev_pagemap *pgmap = NULL;
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int nr_start = *nr;
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pte_t *ptep;
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ptep = pte_offset_map(&pmd, addr);
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do {
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pte_t pte = gup_get_pte(ptep);
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struct page *page;
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/* Similar to the PMD case, NUMA hinting must take slow path */
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if (pte_protnone(pte)) {
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pte_unmap(ptep);
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return 0;
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}
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if (pte_devmap(pte)) {
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pgmap = get_dev_pagemap(pte_pfn(pte), pgmap);
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if (unlikely(!pgmap)) {
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undo_dev_pagemap(nr, nr_start, pages);
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pte_unmap(ptep);
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return 0;
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}
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} else if (!pte_allows_gup(pte_val(pte), write) ||
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pte_special(pte)) {
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pte_unmap(ptep);
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return 0;
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}
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VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
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page = pte_page(pte);
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get_page(page);
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put_dev_pagemap(pgmap);
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SetPageReferenced(page);
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pages[*nr] = page;
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(*nr)++;
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} while (ptep++, addr += PAGE_SIZE, addr != end);
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pte_unmap(ptep - 1);
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return 1;
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}
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static inline void get_head_page_multiple(struct page *page, int nr)
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{
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VM_BUG_ON_PAGE(page != compound_head(page), page);
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VM_BUG_ON_PAGE(page_count(page) == 0, page);
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page_ref_add(page, nr);
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SetPageReferenced(page);
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}
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static int __gup_device_huge_pmd(pmd_t pmd, unsigned long addr,
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unsigned long end, struct page **pages, int *nr)
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{
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int nr_start = *nr;
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unsigned long pfn = pmd_pfn(pmd);
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struct dev_pagemap *pgmap = NULL;
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pfn += (addr & ~PMD_MASK) >> PAGE_SHIFT;
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do {
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struct page *page = pfn_to_page(pfn);
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pgmap = get_dev_pagemap(pfn, pgmap);
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if (unlikely(!pgmap)) {
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undo_dev_pagemap(nr, nr_start, pages);
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return 0;
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}
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SetPageReferenced(page);
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pages[*nr] = page;
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get_page(page);
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put_dev_pagemap(pgmap);
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(*nr)++;
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pfn++;
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} while (addr += PAGE_SIZE, addr != end);
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return 1;
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}
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static noinline int gup_huge_pmd(pmd_t pmd, unsigned long addr,
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unsigned long end, int write, struct page **pages, int *nr)
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{
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struct page *head, *page;
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int refs;
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if (!pte_allows_gup(pmd_val(pmd), write))
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return 0;
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VM_BUG_ON(!pfn_valid(pmd_pfn(pmd)));
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if (pmd_devmap(pmd))
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return __gup_device_huge_pmd(pmd, addr, end, pages, nr);
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/* hugepages are never "special" */
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VM_BUG_ON(pmd_flags(pmd) & _PAGE_SPECIAL);
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refs = 0;
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head = pmd_page(pmd);
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page = head + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
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do {
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VM_BUG_ON_PAGE(compound_head(page) != head, page);
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pages[*nr] = page;
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(*nr)++;
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page++;
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refs++;
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} while (addr += PAGE_SIZE, addr != end);
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get_head_page_multiple(head, refs);
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return 1;
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}
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static int gup_pmd_range(pud_t pud, unsigned long addr, unsigned long end,
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int write, struct page **pages, int *nr)
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{
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unsigned long next;
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pmd_t *pmdp;
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pmdp = pmd_offset(&pud, addr);
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do {
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pmd_t pmd = *pmdp;
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next = pmd_addr_end(addr, end);
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if (pmd_none(pmd))
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return 0;
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if (unlikely(pmd_large(pmd) || !pmd_present(pmd))) {
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/*
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* NUMA hinting faults need to be handled in the GUP
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* slowpath for accounting purposes and so that they
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* can be serialised against THP migration.
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*/
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if (pmd_protnone(pmd))
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return 0;
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if (!gup_huge_pmd(pmd, addr, next, write, pages, nr))
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return 0;
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} else {
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if (!gup_pte_range(pmd, addr, next, write, pages, nr))
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return 0;
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}
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} while (pmdp++, addr = next, addr != end);
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return 1;
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}
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static noinline int gup_huge_pud(pud_t pud, unsigned long addr,
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unsigned long end, int write, struct page **pages, int *nr)
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{
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struct page *head, *page;
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int refs;
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if (!pte_allows_gup(pud_val(pud), write))
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return 0;
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/* hugepages are never "special" */
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VM_BUG_ON(pud_flags(pud) & _PAGE_SPECIAL);
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VM_BUG_ON(!pfn_valid(pud_pfn(pud)));
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refs = 0;
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head = pud_page(pud);
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page = head + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
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do {
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VM_BUG_ON_PAGE(compound_head(page) != head, page);
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pages[*nr] = page;
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(*nr)++;
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page++;
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refs++;
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} while (addr += PAGE_SIZE, addr != end);
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get_head_page_multiple(head, refs);
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return 1;
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}
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static int gup_pud_range(pgd_t pgd, unsigned long addr, unsigned long end,
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int write, struct page **pages, int *nr)
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{
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unsigned long next;
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pud_t *pudp;
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pudp = pud_offset(&pgd, addr);
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do {
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pud_t pud = *pudp;
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next = pud_addr_end(addr, end);
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if (pud_none(pud))
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return 0;
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if (unlikely(pud_large(pud))) {
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if (!gup_huge_pud(pud, addr, next, write, pages, nr))
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return 0;
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} else {
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if (!gup_pmd_range(pud, addr, next, write, pages, nr))
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return 0;
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}
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} while (pudp++, addr = next, addr != end);
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return 1;
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}
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/*
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* Like get_user_pages_fast() except its IRQ-safe in that it won't fall
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* back to the regular GUP.
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*/
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int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
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struct page **pages)
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{
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struct mm_struct *mm = current->mm;
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unsigned long addr, len, end;
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unsigned long next;
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unsigned long flags;
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pgd_t *pgdp;
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int nr = 0;
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start &= PAGE_MASK;
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addr = start;
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len = (unsigned long) nr_pages << PAGE_SHIFT;
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end = start + len;
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if (unlikely(!access_ok(write ? VERIFY_WRITE : VERIFY_READ,
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(void __user *)start, len)))
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return 0;
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/*
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* XXX: batch / limit 'nr', to avoid large irq off latency
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* needs some instrumenting to determine the common sizes used by
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* important workloads (eg. DB2), and whether limiting the batch size
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* will decrease performance.
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*
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* It seems like we're in the clear for the moment. Direct-IO is
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* the main guy that batches up lots of get_user_pages, and even
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* they are limited to 64-at-a-time which is not so many.
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*/
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/*
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* This doesn't prevent pagetable teardown, but does prevent
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* the pagetables and pages from being freed on x86.
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*
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* So long as we atomically load page table pointers versus teardown
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* (which we do on x86, with the above PAE exception), we can follow the
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* address down to the the page and take a ref on it.
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*/
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local_irq_save(flags);
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pgdp = pgd_offset(mm, addr);
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do {
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pgd_t pgd = *pgdp;
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next = pgd_addr_end(addr, end);
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if (pgd_none(pgd))
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break;
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if (!gup_pud_range(pgd, addr, next, write, pages, &nr))
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break;
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} while (pgdp++, addr = next, addr != end);
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local_irq_restore(flags);
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return nr;
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}
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/**
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* get_user_pages_fast() - pin user pages in memory
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* @start: starting user address
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* @nr_pages: number of pages from start to pin
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* @write: whether pages will be written to
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* @pages: array that receives pointers to the pages pinned.
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* Should be at least nr_pages long.
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*
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* Attempt to pin user pages in memory without taking mm->mmap_sem.
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* If not successful, it will fall back to taking the lock and
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* calling get_user_pages().
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*
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* Returns number of pages pinned. This may be fewer than the number
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* requested. If nr_pages is 0 or negative, returns 0. If no pages
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* were pinned, returns -errno.
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*/
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int get_user_pages_fast(unsigned long start, int nr_pages, int write,
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struct page **pages)
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{
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struct mm_struct *mm = current->mm;
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unsigned long addr, len, end;
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unsigned long next;
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pgd_t *pgdp;
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int nr = 0;
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start &= PAGE_MASK;
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addr = start;
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len = (unsigned long) nr_pages << PAGE_SHIFT;
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end = start + len;
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if (end < start)
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goto slow_irqon;
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#ifdef CONFIG_X86_64
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if (end >> __VIRTUAL_MASK_SHIFT)
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goto slow_irqon;
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#endif
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/*
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* XXX: batch / limit 'nr', to avoid large irq off latency
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* needs some instrumenting to determine the common sizes used by
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* important workloads (eg. DB2), and whether limiting the batch size
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* will decrease performance.
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*
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* It seems like we're in the clear for the moment. Direct-IO is
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* the main guy that batches up lots of get_user_pages, and even
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* they are limited to 64-at-a-time which is not so many.
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*/
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/*
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* This doesn't prevent pagetable teardown, but does prevent
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* the pagetables and pages from being freed on x86.
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*
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* So long as we atomically load page table pointers versus teardown
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* (which we do on x86, with the above PAE exception), we can follow the
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* address down to the the page and take a ref on it.
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*/
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local_irq_disable();
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pgdp = pgd_offset(mm, addr);
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do {
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pgd_t pgd = *pgdp;
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next = pgd_addr_end(addr, end);
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if (pgd_none(pgd))
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goto slow;
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if (!gup_pud_range(pgd, addr, next, write, pages, &nr))
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goto slow;
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} while (pgdp++, addr = next, addr != end);
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local_irq_enable();
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VM_BUG_ON(nr != (end - start) >> PAGE_SHIFT);
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return nr;
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{
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int ret;
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slow:
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local_irq_enable();
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slow_irqon:
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/* Try to get the remaining pages with get_user_pages */
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start += nr << PAGE_SHIFT;
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pages += nr;
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ret = get_user_pages_unlocked(start,
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(end - start) >> PAGE_SHIFT,
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write, 0, pages);
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/* Have to be a bit careful with return values */
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if (nr > 0) {
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if (ret < 0)
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ret = nr;
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else
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ret += nr;
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}
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return ret;
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}
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}
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