// 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 #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include /* * 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); } 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; } 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) == INTERRUPT_INST_STORAGE; 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; } // Kernel fault on kernel address is bad if (address >= TASK_SIZE) return true; // Read/write fault blocked by KUAP is bad, it can never succeed. if (bad_kuap_fault(regs, address, is_write)) { pr_crit_ratelimited("Kernel attempted to %s user page (%lx) - exploit attempt? (uid: %d)\n", is_write ? "write" : "read", address, from_kuid(&init_user_ns, current_uid())); // 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. return WARN(true, "Bug: %s fault blocked by KUAP!", is_write ? "Write" : "Read"); } // What's left? Kernel fault on user and allowed by KUAP in the faulting context. return false; } 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; } 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) #else #define page_fault_is_write(__err) ((__err) & DSISR_ISSTORE) #endif #if defined(CONFIG_4xx) || defined(CONFIG_BOOKE) #define page_fault_is_bad(__err) (0) #elif 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 /* * 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 data access * fault, SRR1 & 0x08000000 for an instruction access 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) == INTERRUPT_INST_STORAGE; 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))) { if (kfence_handle_page_fault(address, is_write, regs)) return 0; 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); } interrupt_cond_local_irq_enable(regs); 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); } if (unlikely(access_pkey_error(is_write, is_exec, (error_code & DSISR_KEYFAULT), vma))) return bad_access_pkey(regs, address, vma); 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)) { 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); static __always_inline void __do_page_fault(struct pt_regs *regs) { long err; err = ___do_page_fault(regs, regs->dar, regs->dsisr); if (unlikely(err)) bad_page_fault(regs, err); } DEFINE_INTERRUPT_HANDLER(do_page_fault) { __do_page_fault(regs); } #ifdef CONFIG_PPC_BOOK3S_64 /* Same as do_page_fault but interrupt entry has already run in do_hash_fault */ void hash__do_page_fault(struct pt_regs *regs) { __do_page_fault(regs); } NOKPROBE_SYMBOL(hash__do_page_fault); #endif /* * 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. */ static void __bad_page_fault(struct pt_regs *regs, int sig) { int is_write = page_fault_is_write(regs->dsisr); /* kernel has accessed a bad area */ switch (TRAP(regs)) { case INTERRUPT_DATA_STORAGE: case INTERRUPT_DATA_SEGMENT: case INTERRUPT_H_DATA_STORAGE: 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 INTERRUPT_INST_STORAGE: case INTERRUPT_INST_SEGMENT: pr_alert("BUG: Unable to handle kernel instruction fetch%s", regs->nip < PAGE_SIZE ? " (NULL pointer?)\n" : "\n"); break; case INTERRUPT_ALIGNMENT: 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); } void bad_page_fault(struct pt_regs *regs, int sig) { const struct exception_table_entry *entry; /* Are we prepared to handle this fault? */ entry = search_exception_tables(instruction_pointer(regs)); if (entry) instruction_pointer_set(regs, extable_fixup(entry)); else __bad_page_fault(regs, sig); } #ifdef CONFIG_PPC_BOOK3S_64 DEFINE_INTERRUPT_HANDLER(do_bad_page_fault_segv) { bad_page_fault(regs, SIGSEGV); } #endif