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authorLinus Torvalds <torvalds@linux-foundation.org>2018-10-23 17:05:28 +0100
committerLinus Torvalds <torvalds@linux-foundation.org>2018-10-23 17:05:28 +0100
commit99792e0cea1ed733cdc8d0758677981e0cbebfed (patch)
treeacf6868f48f687dd8667ee4f99c156415ea8ff7b /arch/x86/mm/fault.c
parent382d72a9aa525b56ab8453ce61751fa712414d3d (diff)
parent977e4be5eb714c48a67afc26a6c477f24130a1f2 (diff)
downloadlinux-99792e0cea1ed733cdc8d0758677981e0cbebfed.tar.bz2
Merge branch 'x86-mm-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull x86 mm updates from Ingo Molnar: "Lots of changes in this cycle: - Lots of CPA (change page attribute) optimizations and related cleanups (Thomas Gleixner, Peter Zijstra) - Make lazy TLB mode even lazier (Rik van Riel) - Fault handler cleanups and improvements (Dave Hansen) - kdump, vmcore: Enable kdumping encrypted memory with AMD SME enabled (Lianbo Jiang) - Clean up VM layout documentation (Baoquan He, Ingo Molnar) - ... plus misc other fixes and enhancements" * 'x86-mm-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (51 commits) x86/stackprotector: Remove the call to boot_init_stack_canary() from cpu_startup_entry() x86/mm: Kill stray kernel fault handling comment x86/mm: Do not warn about PCI BIOS W+X mappings resource: Clean it up a bit resource: Fix find_next_iomem_res() iteration issue resource: Include resource end in walk_*() interfaces x86/kexec: Correct KEXEC_BACKUP_SRC_END off-by-one error x86/mm: Remove spurious fault pkey check x86/mm/vsyscall: Consider vsyscall page part of user address space x86/mm: Add vsyscall address helper x86/mm: Fix exception table comments x86/mm: Add clarifying comments for user addr space x86/mm: Break out user address space handling x86/mm: Break out kernel address space handling x86/mm: Clarify hardware vs. software "error_code" x86/mm/tlb: Make lazy TLB mode lazier x86/mm/tlb: Add freed_tables element to flush_tlb_info x86/mm/tlb: Add freed_tables argument to flush_tlb_mm_range smp,cpumask: introduce on_each_cpu_cond_mask smp: use __cpumask_set_cpu in on_each_cpu_cond ...
Diffstat (limited to 'arch/x86/mm/fault.c')
-rw-r--r--arch/x86/mm/fault.c288
1 files changed, 189 insertions, 99 deletions
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 0d45f6debb3a..2b1519bc5381 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -851,6 +851,15 @@ show_signal_msg(struct pt_regs *regs, unsigned long error_code,
show_opcodes(regs, loglvl);
}
+/*
+ * The (legacy) vsyscall page is the long page in the kernel portion
+ * of the address space that has user-accessible permissions.
+ */
+static bool is_vsyscall_vaddr(unsigned long vaddr)
+{
+ return unlikely((vaddr & PAGE_MASK) == VSYSCALL_ADDR);
+}
+
static void
__bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code,
unsigned long address, u32 *pkey, int si_code)
@@ -874,18 +883,6 @@ __bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code,
if (is_errata100(regs, address))
return;
-#ifdef CONFIG_X86_64
- /*
- * Instruction fetch faults in the vsyscall page might need
- * emulation.
- */
- if (unlikely((error_code & X86_PF_INSTR) &&
- ((address & ~0xfff) == VSYSCALL_ADDR))) {
- if (emulate_vsyscall(regs, address))
- return;
- }
-#endif
-
/*
* To avoid leaking information about the kernel page table
* layout, pretend that user-mode accesses to kernel addresses
@@ -1043,19 +1040,13 @@ mm_fault_error(struct pt_regs *regs, unsigned long error_code,
}
}
-static int spurious_fault_check(unsigned long error_code, pte_t *pte)
+static int spurious_kernel_fault_check(unsigned long error_code, pte_t *pte)
{
if ((error_code & X86_PF_WRITE) && !pte_write(*pte))
return 0;
if ((error_code & X86_PF_INSTR) && !pte_exec(*pte))
return 0;
- /*
- * Note: We do not do lazy flushing on protection key
- * changes, so no spurious fault will ever set X86_PF_PK.
- */
- if ((error_code & X86_PF_PK))
- return 1;
return 1;
}
@@ -1082,7 +1073,7 @@ static int spurious_fault_check(unsigned long error_code, pte_t *pte)
* (Optional Invalidation).
*/
static noinline int
-spurious_fault(unsigned long error_code, unsigned long address)
+spurious_kernel_fault(unsigned long error_code, unsigned long address)
{
pgd_t *pgd;
p4d_t *p4d;
@@ -1113,27 +1104,27 @@ spurious_fault(unsigned long error_code, unsigned long address)
return 0;
if (p4d_large(*p4d))
- return spurious_fault_check(error_code, (pte_t *) p4d);
+ return spurious_kernel_fault_check(error_code, (pte_t *) p4d);
pud = pud_offset(p4d, address);
if (!pud_present(*pud))
return 0;
if (pud_large(*pud))
- return spurious_fault_check(error_code, (pte_t *) pud);
+ return spurious_kernel_fault_check(error_code, (pte_t *) pud);
pmd = pmd_offset(pud, address);
if (!pmd_present(*pmd))
return 0;
if (pmd_large(*pmd))
- return spurious_fault_check(error_code, (pte_t *) pmd);
+ return spurious_kernel_fault_check(error_code, (pte_t *) pmd);
pte = pte_offset_kernel(pmd, address);
if (!pte_present(*pte))
return 0;
- ret = spurious_fault_check(error_code, pte);
+ ret = spurious_kernel_fault_check(error_code, pte);
if (!ret)
return 0;
@@ -1141,12 +1132,12 @@ spurious_fault(unsigned long error_code, unsigned long address)
* Make sure we have permissions in PMD.
* If not, then there's a bug in the page tables:
*/
- ret = spurious_fault_check(error_code, (pte_t *) pmd);
+ ret = spurious_kernel_fault_check(error_code, (pte_t *) pmd);
WARN_ONCE(!ret, "PMD has incorrect permission bits\n");
return ret;
}
-NOKPROBE_SYMBOL(spurious_fault);
+NOKPROBE_SYMBOL(spurious_kernel_fault);
int show_unhandled_signals = 1;
@@ -1193,6 +1184,14 @@ access_error(unsigned long error_code, struct vm_area_struct *vma)
static int fault_in_kernel_space(unsigned long address)
{
+ /*
+ * On 64-bit systems, the vsyscall page is at an address above
+ * TASK_SIZE_MAX, but is not considered part of the kernel
+ * address space.
+ */
+ if (IS_ENABLED(CONFIG_X86_64) && is_vsyscall_vaddr(address))
+ return false;
+
return address >= TASK_SIZE_MAX;
}
@@ -1214,31 +1213,23 @@ static inline bool smap_violation(int error_code, struct pt_regs *regs)
}
/*
- * This routine handles page faults. It determines the address,
- * and the problem, and then passes it off to one of the appropriate
- * routines.
+ * Called for all faults where 'address' is part of the kernel address
+ * space. Might get called for faults that originate from *code* that
+ * ran in userspace or the kernel.
*/
-static noinline void
-__do_page_fault(struct pt_regs *regs, unsigned long error_code,
- unsigned long address)
+static void
+do_kern_addr_fault(struct pt_regs *regs, unsigned long hw_error_code,
+ unsigned long address)
{
- struct vm_area_struct *vma;
- struct task_struct *tsk;
- struct mm_struct *mm;
- vm_fault_t fault, major = 0;
- unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
- u32 pkey;
-
- tsk = current;
- mm = tsk->mm;
-
- prefetchw(&mm->mmap_sem);
-
- if (unlikely(kmmio_fault(regs, address)))
- return;
+ /*
+ * Protection keys exceptions only happen on user pages. We
+ * have no user pages in the kernel portion of the address
+ * space, so do not expect them here.
+ */
+ WARN_ON_ONCE(hw_error_code & X86_PF_PK);
/*
- * We fault-in kernel-space virtual memory on-demand. The
+ * We can fault-in kernel-space virtual memory on-demand. The
* 'reference' page table is init_mm.pgd.
*
* NOTE! We MUST NOT take any locks for this case. We may
@@ -1246,41 +1237,74 @@ __do_page_fault(struct pt_regs *regs, unsigned long error_code,
* only copy the information from the master page table,
* nothing more.
*
- * This verifies that the fault happens in kernel space
- * (error_code & 4) == 0, and that the fault was not a
- * protection error (error_code & 9) == 0.
+ * Before doing this on-demand faulting, ensure that the
+ * fault is not any of the following:
+ * 1. A fault on a PTE with a reserved bit set.
+ * 2. A fault caused by a user-mode access. (Do not demand-
+ * fault kernel memory due to user-mode accesses).
+ * 3. A fault caused by a page-level protection violation.
+ * (A demand fault would be on a non-present page which
+ * would have X86_PF_PROT==0).
*/
- if (unlikely(fault_in_kernel_space(address))) {
- if (!(error_code & (X86_PF_RSVD | X86_PF_USER | X86_PF_PROT))) {
- if (vmalloc_fault(address) >= 0)
- return;
- }
-
- /* Can handle a stale RO->RW TLB: */
- if (spurious_fault(error_code, address))
+ if (!(hw_error_code & (X86_PF_RSVD | X86_PF_USER | X86_PF_PROT))) {
+ if (vmalloc_fault(address) >= 0)
return;
+ }
- /* kprobes don't want to hook the spurious faults: */
- if (kprobes_fault(regs))
- return;
- /*
- * Don't take the mm semaphore here. If we fixup a prefetch
- * fault we could otherwise deadlock:
- */
- bad_area_nosemaphore(regs, error_code, address, NULL);
+ /* Was the fault spurious, caused by lazy TLB invalidation? */
+ if (spurious_kernel_fault(hw_error_code, address))
+ return;
+ /* kprobes don't want to hook the spurious faults: */
+ if (kprobes_fault(regs))
return;
- }
+
+ /*
+ * Note, despite being a "bad area", there are quite a few
+ * acceptable reasons to get here, such as erratum fixups
+ * and handling kernel code that can fault, like get_user().
+ *
+ * Don't take the mm semaphore here. If we fixup a prefetch
+ * fault we could otherwise deadlock:
+ */
+ bad_area_nosemaphore(regs, hw_error_code, address, NULL);
+}
+NOKPROBE_SYMBOL(do_kern_addr_fault);
+
+/* Handle faults in the user portion of the address space */
+static inline
+void do_user_addr_fault(struct pt_regs *regs,
+ unsigned long hw_error_code,
+ unsigned long address)
+{
+ unsigned long sw_error_code;
+ struct vm_area_struct *vma;
+ struct task_struct *tsk;
+ struct mm_struct *mm;
+ vm_fault_t fault, major = 0;
+ unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
+ u32 pkey;
+
+ tsk = current;
+ mm = tsk->mm;
/* kprobes don't want to hook the spurious faults: */
if (unlikely(kprobes_fault(regs)))
return;
- if (unlikely(error_code & X86_PF_RSVD))
- pgtable_bad(regs, error_code, address);
+ /*
+ * Reserved bits are never expected to be set on
+ * entries in the user portion of the page tables.
+ */
+ if (unlikely(hw_error_code & X86_PF_RSVD))
+ pgtable_bad(regs, hw_error_code, address);
- if (unlikely(smap_violation(error_code, regs))) {
- bad_area_nosemaphore(regs, error_code, address, NULL);
+ /*
+ * Check for invalid kernel (supervisor) access to user
+ * pages in the user address space.
+ */
+ if (unlikely(smap_violation(hw_error_code, regs))) {
+ bad_area_nosemaphore(regs, hw_error_code, address, NULL);
return;
}
@@ -1289,11 +1313,18 @@ __do_page_fault(struct pt_regs *regs, unsigned long error_code,
* in a region with pagefaults disabled then we must not take the fault
*/
if (unlikely(faulthandler_disabled() || !mm)) {
- bad_area_nosemaphore(regs, error_code, address, NULL);
+ bad_area_nosemaphore(regs, hw_error_code, address, NULL);
return;
}
/*
+ * hw_error_code is literally the "page fault error code" passed to
+ * the kernel directly from the hardware. But, we will shortly be
+ * modifying it in software, so give it a new name.
+ */
+ sw_error_code = hw_error_code;
+
+ /*
* It's safe to allow irq's after cr2 has been saved and the
* vmalloc fault has been handled.
*
@@ -1302,7 +1333,26 @@ __do_page_fault(struct pt_regs *regs, unsigned long error_code,
*/
if (user_mode(regs)) {
local_irq_enable();
- error_code |= X86_PF_USER;
+ /*
+ * Up to this point, X86_PF_USER set in hw_error_code
+ * indicated a user-mode access. But, after this,
+ * X86_PF_USER in sw_error_code will indicate either
+ * that, *or* an implicit kernel(supervisor)-mode access
+ * which originated from user mode.
+ */
+ if (!(hw_error_code & X86_PF_USER)) {
+ /*
+ * The CPU was in user mode, but the CPU says
+ * the fault was not a user-mode access.
+ * Must be an implicit kernel-mode access,
+ * which we do not expect to happen in the
+ * user address space.
+ */
+ pr_warn_once("kernel-mode error from user-mode: %lx\n",
+ hw_error_code);
+
+ sw_error_code |= X86_PF_USER;
+ }
flags |= FAULT_FLAG_USER;
} else {
if (regs->flags & X86_EFLAGS_IF)
@@ -1311,31 +1361,49 @@ __do_page_fault(struct pt_regs *regs, unsigned long error_code,
perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address);
- if (error_code & X86_PF_WRITE)
+ if (sw_error_code & X86_PF_WRITE)
flags |= FAULT_FLAG_WRITE;
- if (error_code & X86_PF_INSTR)
+ if (sw_error_code & X86_PF_INSTR)
flags |= FAULT_FLAG_INSTRUCTION;
+#ifdef CONFIG_X86_64
/*
- * When running in the kernel we expect faults to occur only to
- * addresses in user space. All other faults represent errors in
- * the kernel and should generate an OOPS. Unfortunately, in the
- * case of an erroneous fault occurring in a code path which already
- * holds mmap_sem we will deadlock attempting to validate the fault
- * against the address space. Luckily the kernel only validly
- * references user space from well defined areas of code, which are
- * listed in the exceptions table.
+ * Instruction fetch faults in the vsyscall page might need
+ * emulation. The vsyscall page is at a high address
+ * (>PAGE_OFFSET), but is considered to be part of the user
+ * address space.
*
- * As the vast majority of faults will be valid we will only perform
- * the source reference check when there is a possibility of a
- * deadlock. Attempt to lock the address space, if we cannot we then
- * validate the source. If this is invalid we can skip the address
- * space check, thus avoiding the deadlock:
+ * The vsyscall page does not have a "real" VMA, so do this
+ * emulation before we go searching for VMAs.
+ */
+ if ((sw_error_code & X86_PF_INSTR) && is_vsyscall_vaddr(address)) {
+ if (emulate_vsyscall(regs, address))
+ return;
+ }
+#endif
+
+ /*
+ * Kernel-mode access to the user address space should only occur
+ * on well-defined single instructions listed in the exception
+ * tables. But, an erroneous kernel fault occurring outside one of
+ * those areas which also holds mmap_sem might deadlock attempting
+ * to validate the fault against the address space.
+ *
+ * Only do the expensive exception table search when we might be at
+ * risk of a deadlock. This happens if we
+ * 1. Failed to acquire mmap_sem, and
+ * 2. The access did not originate in userspace. Note: either the
+ * hardware or earlier page fault code may set X86_PF_USER
+ * in sw_error_code.
*/
if (unlikely(!down_read_trylock(&mm->mmap_sem))) {
- if (!(error_code & X86_PF_USER) &&
+ if (!(sw_error_code & X86_PF_USER) &&
!search_exception_tables(regs->ip)) {
- bad_area_nosemaphore(regs, error_code, address, NULL);
+ /*
+ * Fault from code in kernel from
+ * which we do not expect faults.
+ */
+ bad_area_nosemaphore(regs, sw_error_code, address, NULL);
return;
}
retry:
@@ -1351,16 +1419,16 @@ retry:
vma = find_vma(mm, address);
if (unlikely(!vma)) {
- bad_area(regs, error_code, address);
+ bad_area(regs, sw_error_code, address);
return;
}
if (likely(vma->vm_start <= address))
goto good_area;
if (unlikely(!(vma->vm_flags & VM_GROWSDOWN))) {
- bad_area(regs, error_code, address);
+ bad_area(regs, sw_error_code, address);
return;
}
- if (error_code & X86_PF_USER) {
+ if (sw_error_code & X86_PF_USER) {
/*
* Accessing the stack below %sp is always a bug.
* The large cushion allows instructions like enter
@@ -1368,12 +1436,12 @@ retry:
* 32 pointers and then decrements %sp by 65535.)
*/
if (unlikely(address + 65536 + 32 * sizeof(unsigned long) < regs->sp)) {
- bad_area(regs, error_code, address);
+ bad_area(regs, sw_error_code, address);
return;
}
}
if (unlikely(expand_stack(vma, address))) {
- bad_area(regs, error_code, address);
+ bad_area(regs, sw_error_code, address);
return;
}
@@ -1382,8 +1450,8 @@ retry:
* we can handle it..
*/
good_area:
- if (unlikely(access_error(error_code, vma))) {
- bad_area_access_error(regs, error_code, address, vma);
+ if (unlikely(access_error(sw_error_code, vma))) {
+ bad_area_access_error(regs, sw_error_code, address, vma);
return;
}
@@ -1425,13 +1493,13 @@ good_area:
return;
/* Not returning to user mode? Handle exceptions or die: */
- no_context(regs, error_code, address, SIGBUS, BUS_ADRERR);
+ no_context(regs, sw_error_code, address, SIGBUS, BUS_ADRERR);
return;
}
up_read(&mm->mmap_sem);
if (unlikely(fault & VM_FAULT_ERROR)) {
- mm_fault_error(regs, error_code, address, &pkey, fault);
+ mm_fault_error(regs, sw_error_code, address, &pkey, fault);
return;
}
@@ -1449,6 +1517,28 @@ good_area:
check_v8086_mode(regs, address, tsk);
}
+NOKPROBE_SYMBOL(do_user_addr_fault);
+
+/*
+ * This routine handles page faults. It determines the address,
+ * and the problem, and then passes it off to one of the appropriate
+ * routines.
+ */
+static noinline void
+__do_page_fault(struct pt_regs *regs, unsigned long hw_error_code,
+ unsigned long address)
+{
+ prefetchw(&current->mm->mmap_sem);
+
+ if (unlikely(kmmio_fault(regs, address)))
+ return;
+
+ /* Was the fault on kernel-controlled part of the address space? */
+ if (unlikely(fault_in_kernel_space(address)))
+ do_kern_addr_fault(regs, hw_error_code, address);
+ else
+ do_user_addr_fault(regs, hw_error_code, address);
+}
NOKPROBE_SYMBOL(__do_page_fault);
static nokprobe_inline void