diff options
Diffstat (limited to 'arch/powerpc/mm/fault.c')
| -rw-r--r-- | arch/powerpc/mm/fault.c | 601 |
1 files changed, 601 insertions, 0 deletions
diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c new file mode 100644 index 000000000..55fdba8ba --- /dev/null +++ b/arch/powerpc/mm/fault.c @@ -0,0 +1,601 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* + * PowerPC version + * Copyright (C) 1995-1996 Gary Thomas (gdt@linuxppc.org) + * + * Derived from "arch/i386/mm/fault.c" + * Copyright (C) 1991, 1992, 1993, 1994 Linus Torvalds + * + * Modified by Cort Dougan and Paul Mackerras. + * + * Modified for PPC64 by Dave Engebretsen (engebret@ibm.com) + */ + +#include <linux/signal.h> +#include <linux/sched.h> +#include <linux/sched/task_stack.h> +#include <linux/kernel.h> +#include <linux/errno.h> +#include <linux/string.h> +#include <linux/types.h> +#include <linux/pagemap.h> +#include <linux/ptrace.h> +#include <linux/mman.h> +#include <linux/mm.h> +#include <linux/interrupt.h> +#include <linux/highmem.h> +#include <linux/extable.h> +#include <linux/kprobes.h> +#include <linux/kdebug.h> +#include <linux/perf_event.h> +#include <linux/ratelimit.h> +#include <linux/context_tracking.h> +#include <linux/hugetlb.h> +#include <linux/uaccess.h> + +#include <asm/firmware.h> +#include <asm/page.h> +#include <asm/mmu.h> +#include <asm/mmu_context.h> +#include <asm/siginfo.h> +#include <asm/debug.h> +#include <asm/kup.h> +#include <asm/inst.h> + + +/* + * do_page_fault error handling helpers + */ + +static int +__bad_area_nosemaphore(struct pt_regs *regs, unsigned long address, int si_code) +{ + /* + * If we are in kernel mode, bail out with a SEGV, this will + * be caught by the assembly which will restore the non-volatile + * registers before calling bad_page_fault() + */ + if (!user_mode(regs)) + return SIGSEGV; + + _exception(SIGSEGV, regs, si_code, address); + + return 0; +} + +static noinline int bad_area_nosemaphore(struct pt_regs *regs, unsigned long address) +{ + return __bad_area_nosemaphore(regs, address, SEGV_MAPERR); +} + +static int __bad_area(struct pt_regs *regs, unsigned long address, int si_code) +{ + struct mm_struct *mm = current->mm; + + /* + * Something tried to access memory that isn't in our memory map.. + * Fix it, but check if it's kernel or user first.. + */ + mmap_read_unlock(mm); + + return __bad_area_nosemaphore(regs, address, si_code); +} + +static noinline int bad_area(struct pt_regs *regs, unsigned long address) +{ + return __bad_area(regs, address, SEGV_MAPERR); +} + +#ifdef CONFIG_PPC_MEM_KEYS +static noinline int bad_access_pkey(struct pt_regs *regs, unsigned long address, + struct vm_area_struct *vma) +{ + struct mm_struct *mm = current->mm; + int pkey; + + /* + * We don't try to fetch the pkey from page table because reading + * page table without locking doesn't guarantee stable pte value. + * Hence the pkey value that we return to userspace can be different + * from the pkey that actually caused access error. + * + * It does *not* guarantee that the VMA we find here + * was the one that we faulted on. + * + * 1. T1 : mprotect_key(foo, PAGE_SIZE, pkey=4); + * 2. T1 : set AMR to deny access to pkey=4, touches, page + * 3. T1 : faults... + * 4. T2: mprotect_key(foo, PAGE_SIZE, pkey=5); + * 5. T1 : enters fault handler, takes mmap_lock, etc... + * 6. T1 : reaches here, sees vma_pkey(vma)=5, when we really + * faulted on a pte with its pkey=4. + */ + pkey = vma_pkey(vma); + + mmap_read_unlock(mm); + + /* + * If we are in kernel mode, bail out with a SEGV, this will + * be caught by the assembly which will restore the non-volatile + * registers before calling bad_page_fault() + */ + if (!user_mode(regs)) + return SIGSEGV; + + _exception_pkey(regs, address, pkey); + + return 0; +} +#endif + +static noinline int bad_access(struct pt_regs *regs, unsigned long address) +{ + return __bad_area(regs, address, SEGV_ACCERR); +} + +static int do_sigbus(struct pt_regs *regs, unsigned long address, + vm_fault_t fault) +{ + if (!user_mode(regs)) + return SIGBUS; + + current->thread.trap_nr = BUS_ADRERR; +#ifdef CONFIG_MEMORY_FAILURE + if (fault & (VM_FAULT_HWPOISON|VM_FAULT_HWPOISON_LARGE)) { + unsigned int lsb = 0; /* shutup gcc */ + + pr_err("MCE: Killing %s:%d due to hardware memory corruption fault at %lx\n", + current->comm, current->pid, address); + + if (fault & VM_FAULT_HWPOISON_LARGE) + lsb = hstate_index_to_shift(VM_FAULT_GET_HINDEX(fault)); + if (fault & VM_FAULT_HWPOISON) + lsb = PAGE_SHIFT; + + force_sig_mceerr(BUS_MCEERR_AR, (void __user *)address, lsb); + return 0; + } + +#endif + force_sig_fault(SIGBUS, BUS_ADRERR, (void __user *)address); + return 0; +} + +static int mm_fault_error(struct pt_regs *regs, unsigned long addr, + vm_fault_t fault) +{ + /* + * Kernel page fault interrupted by SIGKILL. We have no reason to + * continue processing. + */ + if (fatal_signal_pending(current) && !user_mode(regs)) + return SIGKILL; + + /* Out of memory */ + if (fault & VM_FAULT_OOM) { + /* + * We ran out of memory, or some other thing happened to us that + * made us unable to handle the page fault gracefully. + */ + if (!user_mode(regs)) + return SIGSEGV; + pagefault_out_of_memory(); + } else { + if (fault & (VM_FAULT_SIGBUS|VM_FAULT_HWPOISON| + VM_FAULT_HWPOISON_LARGE)) + return do_sigbus(regs, addr, fault); + else if (fault & VM_FAULT_SIGSEGV) + return bad_area_nosemaphore(regs, addr); + else + BUG(); + } + return 0; +} + +/* Is this a bad kernel fault ? */ +static bool bad_kernel_fault(struct pt_regs *regs, unsigned long error_code, + unsigned long address, bool is_write) +{ + int is_exec = TRAP(regs) == 0x400; + + if (is_exec) { + pr_crit_ratelimited("kernel tried to execute %s page (%lx) - exploit attempt? (uid: %d)\n", + address >= TASK_SIZE ? "exec-protected" : "user", + address, + from_kuid(&init_user_ns, current_uid())); + + // Kernel exec fault is always bad + return true; + } + + if (!is_exec && address < TASK_SIZE && (error_code & DSISR_PROTFAULT) && + !search_exception_tables(regs->nip)) { + pr_crit_ratelimited("Kernel attempted to access user page (%lx) - exploit attempt? (uid: %d)\n", + address, + from_kuid(&init_user_ns, current_uid())); + } + + // Kernel fault on kernel address is bad + if (address >= TASK_SIZE) + return true; + + // Fault on user outside of certain regions (eg. copy_tofrom_user()) is bad + if (!search_exception_tables(regs->nip)) + return true; + + // Read/write fault in a valid region (the exception table search passed + // above), but blocked by KUAP is bad, it can never succeed. + if (bad_kuap_fault(regs, address, is_write)) + return true; + + // What's left? Kernel fault on user in well defined regions (extable + // matched), and allowed by KUAP in the faulting context. + return false; +} + +#ifdef CONFIG_PPC_MEM_KEYS +static bool access_pkey_error(bool is_write, bool is_exec, bool is_pkey, + struct vm_area_struct *vma) +{ + /* + * Make sure to check the VMA so that we do not perform + * faults just to hit a pkey fault as soon as we fill in a + * page. Only called for current mm, hence foreign == 0 + */ + if (!arch_vma_access_permitted(vma, is_write, is_exec, 0)) + return true; + + return false; +} +#endif + +static bool access_error(bool is_write, bool is_exec, struct vm_area_struct *vma) +{ + /* + * Allow execution from readable areas if the MMU does not + * provide separate controls over reading and executing. + * + * Note: That code used to not be enabled for 4xx/BookE. + * It is now as I/D cache coherency for these is done at + * set_pte_at() time and I see no reason why the test + * below wouldn't be valid on those processors. This -may- + * break programs compiled with a really old ABI though. + */ + if (is_exec) { + return !(vma->vm_flags & VM_EXEC) && + (cpu_has_feature(CPU_FTR_NOEXECUTE) || + !(vma->vm_flags & (VM_READ | VM_WRITE))); + } + + if (is_write) { + if (unlikely(!(vma->vm_flags & VM_WRITE))) + return true; + return false; + } + + if (unlikely(!vma_is_accessible(vma))) + return true; + /* + * We should ideally do the vma pkey access check here. But in the + * fault path, handle_mm_fault() also does the same check. To avoid + * these multiple checks, we skip it here and handle access error due + * to pkeys later. + */ + return false; +} + +#ifdef CONFIG_PPC_SMLPAR +static inline void cmo_account_page_fault(void) +{ + if (firmware_has_feature(FW_FEATURE_CMO)) { + u32 page_ins; + + preempt_disable(); + page_ins = be32_to_cpu(get_lppaca()->page_ins); + page_ins += 1 << PAGE_FACTOR; + get_lppaca()->page_ins = cpu_to_be32(page_ins); + preempt_enable(); + } +} +#else +static inline void cmo_account_page_fault(void) { } +#endif /* CONFIG_PPC_SMLPAR */ + +static void sanity_check_fault(bool is_write, bool is_user, + unsigned long error_code, unsigned long address) +{ + /* + * Userspace trying to access kernel address, we get PROTFAULT for that. + */ + if (is_user && address >= TASK_SIZE) { + if ((long)address == -1) + return; + + pr_crit_ratelimited("%s[%d]: User access of kernel address (%lx) - exploit attempt? (uid: %d)\n", + current->comm, current->pid, address, + from_kuid(&init_user_ns, current_uid())); + return; + } + + if (!IS_ENABLED(CONFIG_PPC_BOOK3S)) + return; + + /* + * For hash translation mode, we should never get a + * PROTFAULT. Any update to pte to reduce access will result in us + * removing the hash page table entry, thus resulting in a DSISR_NOHPTE + * fault instead of DSISR_PROTFAULT. + * + * A pte update to relax the access will not result in a hash page table + * entry invalidate and hence can result in DSISR_PROTFAULT. + * ptep_set_access_flags() doesn't do a hpte flush. This is why we have + * the special !is_write in the below conditional. + * + * For platforms that doesn't supports coherent icache and do support + * per page noexec bit, we do setup things such that we do the + * sync between D/I cache via fault. But that is handled via low level + * hash fault code (hash_page_do_lazy_icache()) and we should not reach + * here in such case. + * + * For wrong access that can result in PROTFAULT, the above vma->vm_flags + * check should handle those and hence we should fall to the bad_area + * handling correctly. + * + * For embedded with per page exec support that doesn't support coherent + * icache we do get PROTFAULT and we handle that D/I cache sync in + * set_pte_at while taking the noexec/prot fault. Hence this is WARN_ON + * is conditional for server MMU. + * + * For radix, we can get prot fault for autonuma case, because radix + * page table will have them marked noaccess for user. + */ + if (radix_enabled() || is_write) + return; + + WARN_ON_ONCE(error_code & DSISR_PROTFAULT); +} + +/* + * Define the correct "is_write" bit in error_code based + * on the processor family + */ +#if (defined(CONFIG_4xx) || defined(CONFIG_BOOKE)) +#define page_fault_is_write(__err) ((__err) & ESR_DST) +#define page_fault_is_bad(__err) (0) +#else +#define page_fault_is_write(__err) ((__err) & DSISR_ISSTORE) +#if defined(CONFIG_PPC_8xx) +#define page_fault_is_bad(__err) ((__err) & DSISR_NOEXEC_OR_G) +#elif defined(CONFIG_PPC64) +#define page_fault_is_bad(__err) ((__err) & DSISR_BAD_FAULT_64S) +#else +#define page_fault_is_bad(__err) ((__err) & DSISR_BAD_FAULT_32S) +#endif +#endif + +/* + * For 600- and 800-family processors, the error_code parameter is DSISR + * for a data fault, SRR1 for an instruction fault. For 400-family processors + * the error_code parameter is ESR for a data fault, 0 for an instruction + * fault. + * For 64-bit processors, the error_code parameter is + * - DSISR for a non-SLB data access fault, + * - SRR1 & 0x08000000 for a non-SLB instruction access fault + * - 0 any SLB fault. + * + * The return value is 0 if the fault was handled, or the signal + * number if this is a kernel fault that can't be handled here. + */ +static int __do_page_fault(struct pt_regs *regs, unsigned long address, + unsigned long error_code) +{ + struct vm_area_struct * vma; + struct mm_struct *mm = current->mm; + unsigned int flags = FAULT_FLAG_DEFAULT; + int is_exec = TRAP(regs) == 0x400; + int is_user = user_mode(regs); + int is_write = page_fault_is_write(error_code); + vm_fault_t fault, major = 0; + bool kprobe_fault = kprobe_page_fault(regs, 11); + + if (unlikely(debugger_fault_handler(regs) || kprobe_fault)) + return 0; + + if (unlikely(page_fault_is_bad(error_code))) { + if (is_user) { + _exception(SIGBUS, regs, BUS_OBJERR, address); + return 0; + } + return SIGBUS; + } + + /* Additional sanity check(s) */ + sanity_check_fault(is_write, is_user, error_code, address); + + /* + * The kernel should never take an execute fault nor should it + * take a page fault to a kernel address or a page fault to a user + * address outside of dedicated places + */ + if (unlikely(!is_user && bad_kernel_fault(regs, error_code, address, is_write))) + return SIGSEGV; + + /* + * If we're in an interrupt, have no user context or are running + * in a region with pagefaults disabled then we must not take the fault + */ + if (unlikely(faulthandler_disabled() || !mm)) { + if (is_user) + printk_ratelimited(KERN_ERR "Page fault in user mode" + " with faulthandler_disabled()=%d" + " mm=%p\n", + faulthandler_disabled(), mm); + return bad_area_nosemaphore(regs, address); + } + + /* We restore the interrupt state now */ + if (!arch_irq_disabled_regs(regs)) + local_irq_enable(); + + perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address); + + /* + * We want to do this outside mmap_lock, because reading code around nip + * can result in fault, which will cause a deadlock when called with + * mmap_lock held + */ + if (is_user) + flags |= FAULT_FLAG_USER; + if (is_write) + flags |= FAULT_FLAG_WRITE; + if (is_exec) + flags |= FAULT_FLAG_INSTRUCTION; + + /* 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_lock + * 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. + * + * 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. + */ + if (unlikely(!mmap_read_trylock(mm))) { + if (!is_user && !search_exception_tables(regs->nip)) + return bad_area_nosemaphore(regs, address); + +retry: + mmap_read_lock(mm); + } else { + /* + * The above down_read_trylock() might have succeeded in + * which case we'll have missed the might_sleep() from + * down_read(): + */ + might_sleep(); + } + + vma = find_vma(mm, address); + if (unlikely(!vma)) + return bad_area(regs, address); + + if (unlikely(vma->vm_start > address)) { + if (unlikely(!(vma->vm_flags & VM_GROWSDOWN))) + return bad_area(regs, address); + + if (unlikely(expand_stack(vma, address))) + return bad_area(regs, address); + } + +#ifdef CONFIG_PPC_MEM_KEYS + if (unlikely(access_pkey_error(is_write, is_exec, + (error_code & DSISR_KEYFAULT), vma))) + return bad_access_pkey(regs, address, vma); +#endif /* CONFIG_PPC_MEM_KEYS */ + + if (unlikely(access_error(is_write, is_exec, vma))) + return bad_access(regs, address); + + /* + * If for any reason at all we couldn't handle the fault, + * make sure we exit gracefully rather than endlessly redo + * the fault. + */ + fault = handle_mm_fault(vma, address, flags, regs); + + major |= fault & VM_FAULT_MAJOR; + + if (fault_signal_pending(fault, regs)) + return user_mode(regs) ? 0 : SIGBUS; + + /* + * Handle the retry right now, the mmap_lock has been released in that + * case. + */ + if (unlikely(fault & VM_FAULT_RETRY)) { + if (flags & FAULT_FLAG_ALLOW_RETRY) { + flags |= FAULT_FLAG_TRIED; + goto retry; + } + } + + mmap_read_unlock(current->mm); + + if (unlikely(fault & VM_FAULT_ERROR)) + return mm_fault_error(regs, address, fault); + + /* + * Major/minor page fault accounting. + */ + if (major) + cmo_account_page_fault(); + + return 0; +} +NOKPROBE_SYMBOL(__do_page_fault); + +int do_page_fault(struct pt_regs *regs, unsigned long address, + unsigned long error_code) +{ + enum ctx_state prev_state = exception_enter(); + int rc = __do_page_fault(regs, address, error_code); + exception_exit(prev_state); + return rc; +} +NOKPROBE_SYMBOL(do_page_fault); + +/* + * bad_page_fault is called when we have a bad access from the kernel. + * It is called from the DSI and ISI handlers in head.S and from some + * of the procedures in traps.c. + */ +void bad_page_fault(struct pt_regs *regs, unsigned long address, int sig) +{ + const struct exception_table_entry *entry; + int is_write = page_fault_is_write(regs->dsisr); + + /* Are we prepared to handle this fault? */ + if ((entry = search_exception_tables(regs->nip)) != NULL) { + regs->nip = extable_fixup(entry); + return; + } + + /* kernel has accessed a bad area */ + + switch (TRAP(regs)) { + case 0x300: + case 0x380: + case 0xe00: + pr_alert("BUG: %s on %s at 0x%08lx\n", + regs->dar < PAGE_SIZE ? "Kernel NULL pointer dereference" : + "Unable to handle kernel data access", + is_write ? "write" : "read", regs->dar); + break; + case 0x400: + case 0x480: + pr_alert("BUG: Unable to handle kernel instruction fetch%s", + regs->nip < PAGE_SIZE ? " (NULL pointer?)\n" : "\n"); + break; + case 0x600: + pr_alert("BUG: Unable to handle kernel unaligned access at 0x%08lx\n", + regs->dar); + break; + default: + pr_alert("BUG: Unable to handle unknown paging fault at 0x%08lx\n", + regs->dar); + break; + } + printk(KERN_ALERT "Faulting instruction address: 0x%08lx\n", + regs->nip); + + if (task_stack_end_corrupted(current)) + printk(KERN_ALERT "Thread overran stack, or stack corrupted\n"); + + die("Kernel access of bad area", regs, sig); +} |