1 // SPDX-License-Identifier: GPL-2.0 2 #include <linux/mm.h> 3 #include <linux/sched.h> 4 #include <linux/sched/debug.h> 5 #include <linux/init_task.h> 6 #include <linux/fs.h> 7 8 #include <linux/uaccess.h> 9 #include <asm/processor.h> 10 #include <asm/desc.h> 11 #include <asm/traps.h> 12 #include <asm/doublefault.h> 13 14 #define ptr_ok(x) ((x) > PAGE_OFFSET && (x) < PAGE_OFFSET + MAXMEM) 15 16 #define TSS(x) this_cpu_read(cpu_tss_rw.x86_tss.x) 17 18 static void set_df_gdt_entry(unsigned int cpu); 19 20 /* 21 * Called by double_fault with CR0.TS and EFLAGS.NT cleared. The CPU thinks 22 * we're running the doublefault task. Cannot return. 23 */ 24 asmlinkage noinstr void __noreturn doublefault_shim(void) 25 { 26 unsigned long cr2; 27 struct pt_regs regs; 28 29 BUILD_BUG_ON(sizeof(struct doublefault_stack) != PAGE_SIZE); 30 31 cr2 = native_read_cr2(); 32 33 /* Reset back to the normal kernel task. */ 34 force_reload_TR(); 35 set_df_gdt_entry(smp_processor_id()); 36 37 trace_hardirqs_off(); 38 39 /* 40 * Fill in pt_regs. A downside of doing this in C is that the unwinder 41 * won't see it (no ENCODE_FRAME_POINTER), so a nested stack dump 42 * won't successfully unwind to the source of the double fault. 43 * The main dump from exc_double_fault() is fine, though, since it 44 * uses these regs directly. 45 * 46 * If anyone ever cares, this could be moved to asm. 47 */ 48 regs.ss = TSS(ss); 49 regs.__ssh = 0; 50 regs.sp = TSS(sp); 51 regs.flags = TSS(flags); 52 regs.cs = TSS(cs); 53 /* We won't go through the entry asm, so we can leave __csh as 0. */ 54 regs.__csh = 0; 55 regs.ip = TSS(ip); 56 regs.orig_ax = 0; 57 regs.gs = TSS(gs); 58 regs.__gsh = 0; 59 regs.fs = TSS(fs); 60 regs.__fsh = 0; 61 regs.es = TSS(es); 62 regs.__esh = 0; 63 regs.ds = TSS(ds); 64 regs.__dsh = 0; 65 regs.ax = TSS(ax); 66 regs.bp = TSS(bp); 67 regs.di = TSS(di); 68 regs.si = TSS(si); 69 regs.dx = TSS(dx); 70 regs.cx = TSS(cx); 71 regs.bx = TSS(bx); 72 73 exc_double_fault(®s, 0, cr2); 74 75 /* 76 * x86_32 does not save the original CR3 anywhere on a task switch. 77 * This means that, even if we wanted to return, we would need to find 78 * some way to reconstruct CR3. We could make a credible guess based 79 * on cpu_tlbstate, but that would be racy and would not account for 80 * PTI. 81 */ 82 panic("cannot return from double fault\n"); 83 } 84 85 DEFINE_PER_CPU_PAGE_ALIGNED(struct doublefault_stack, doublefault_stack) = { 86 .tss = { 87 /* 88 * No sp0 or ss0 -- we never run CPL != 0 with this TSS 89 * active. sp is filled in later. 90 */ 91 .ldt = 0, 92 .io_bitmap_base = IO_BITMAP_OFFSET_INVALID, 93 94 .ip = (unsigned long) asm_exc_double_fault, 95 .flags = X86_EFLAGS_FIXED, 96 .es = __USER_DS, 97 .cs = __KERNEL_CS, 98 .ss = __KERNEL_DS, 99 .ds = __USER_DS, 100 .fs = __KERNEL_PERCPU, 101 .gs = 0, 102 103 .__cr3 = __pa_nodebug(swapper_pg_dir), 104 }, 105 }; 106 107 static void set_df_gdt_entry(unsigned int cpu) 108 { 109 /* Set up doublefault TSS pointer in the GDT */ 110 __set_tss_desc(cpu, GDT_ENTRY_DOUBLEFAULT_TSS, 111 &get_cpu_entry_area(cpu)->doublefault_stack.tss); 112 113 } 114 115 void doublefault_init_cpu_tss(void) 116 { 117 unsigned int cpu = smp_processor_id(); 118 struct cpu_entry_area *cea = get_cpu_entry_area(cpu); 119 120 /* 121 * The linker isn't smart enough to initialize percpu variables that 122 * point to other places in percpu space. 123 */ 124 this_cpu_write(doublefault_stack.tss.sp, 125 (unsigned long)&cea->doublefault_stack.stack + 126 sizeof(doublefault_stack.stack)); 127 128 set_df_gdt_entry(cpu); 129 } 130