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