xref: /openbmc/linux/arch/x86/kernel/doublefault_32.c (revision 7d8d8cfdee9a7bd6f9682f253fa98efdd8048a9e)
1e99b6f46SAndy Lutomirski // SPDX-License-Identifier: GPL-2.0
2e99b6f46SAndy Lutomirski #include <linux/mm.h>
3e99b6f46SAndy Lutomirski #include <linux/sched.h>
4e99b6f46SAndy Lutomirski #include <linux/sched/debug.h>
5e99b6f46SAndy Lutomirski #include <linux/init_task.h>
6e99b6f46SAndy Lutomirski #include <linux/fs.h>
7e99b6f46SAndy Lutomirski 
8e99b6f46SAndy Lutomirski #include <linux/uaccess.h>
9e99b6f46SAndy Lutomirski #include <asm/pgtable.h>
10e99b6f46SAndy Lutomirski #include <asm/processor.h>
11e99b6f46SAndy Lutomirski #include <asm/desc.h>
12*7d8d8cfdSAndy Lutomirski #include <asm/traps.h>
13e99b6f46SAndy Lutomirski 
14*7d8d8cfdSAndy Lutomirski extern void double_fault(void);
15e99b6f46SAndy Lutomirski #define ptr_ok(x) ((x) > PAGE_OFFSET && (x) < PAGE_OFFSET + MAXMEM)
16e99b6f46SAndy Lutomirski 
17*7d8d8cfdSAndy Lutomirski #define TSS(x) this_cpu_read(cpu_tss_rw.x86_tss.x)
18*7d8d8cfdSAndy Lutomirski 
19*7d8d8cfdSAndy Lutomirski static void set_df_gdt_entry(unsigned int cpu);
20*7d8d8cfdSAndy Lutomirski 
21*7d8d8cfdSAndy Lutomirski /*
22*7d8d8cfdSAndy Lutomirski  * Called by double_fault with CR0.TS and EFLAGS.NT cleared.  The CPU thinks
23*7d8d8cfdSAndy Lutomirski  * we're running the doublefault task.  Cannot return.
24*7d8d8cfdSAndy Lutomirski  */
25*7d8d8cfdSAndy Lutomirski asmlinkage notrace void __noreturn doublefault_shim(void)
26e99b6f46SAndy Lutomirski {
27*7d8d8cfdSAndy Lutomirski 	unsigned long cr2;
28*7d8d8cfdSAndy Lutomirski 	struct pt_regs regs;
29e99b6f46SAndy Lutomirski 
30dc4e0021SAndy Lutomirski 	BUILD_BUG_ON(sizeof(struct doublefault_stack) != PAGE_SIZE);
31dc4e0021SAndy Lutomirski 
32*7d8d8cfdSAndy Lutomirski 	cr2 = native_read_cr2();
33e99b6f46SAndy Lutomirski 
34*7d8d8cfdSAndy Lutomirski 	/* Reset back to the normal kernel task. */
35*7d8d8cfdSAndy Lutomirski 	force_reload_TR();
36*7d8d8cfdSAndy Lutomirski 	set_df_gdt_entry(smp_processor_id());
37e99b6f46SAndy Lutomirski 
38*7d8d8cfdSAndy Lutomirski 	trace_hardirqs_off();
39e99b6f46SAndy Lutomirski 
40*7d8d8cfdSAndy Lutomirski 	/*
41*7d8d8cfdSAndy Lutomirski 	 * Fill in pt_regs.  A downside of doing this in C is that the unwinder
42*7d8d8cfdSAndy Lutomirski 	 * won't see it (no ENCODE_FRAME_POINTER), so a nested stack dump
43*7d8d8cfdSAndy Lutomirski 	 * won't successfully unwind to the source of the double fault.
44*7d8d8cfdSAndy Lutomirski 	 * The main dump from do_double_fault() is fine, though, since it
45*7d8d8cfdSAndy Lutomirski 	 * uses these regs directly.
46*7d8d8cfdSAndy Lutomirski 	 *
47*7d8d8cfdSAndy Lutomirski 	 * If anyone ever cares, this could be moved to asm.
48*7d8d8cfdSAndy Lutomirski 	 */
49*7d8d8cfdSAndy Lutomirski 	regs.ss		= TSS(ss);
50*7d8d8cfdSAndy Lutomirski 	regs.__ssh	= 0;
51*7d8d8cfdSAndy Lutomirski 	regs.sp		= TSS(sp);
52*7d8d8cfdSAndy Lutomirski 	regs.flags	= TSS(flags);
53*7d8d8cfdSAndy Lutomirski 	regs.cs		= TSS(cs);
54*7d8d8cfdSAndy Lutomirski 	/* We won't go through the entry asm, so we can leave __csh as 0. */
55*7d8d8cfdSAndy Lutomirski 	regs.__csh	= 0;
56*7d8d8cfdSAndy Lutomirski 	regs.ip		= TSS(ip);
57*7d8d8cfdSAndy Lutomirski 	regs.orig_ax	= 0;
58*7d8d8cfdSAndy Lutomirski 	regs.gs		= TSS(gs);
59*7d8d8cfdSAndy Lutomirski 	regs.__gsh	= 0;
60*7d8d8cfdSAndy Lutomirski 	regs.fs		= TSS(fs);
61*7d8d8cfdSAndy Lutomirski 	regs.__fsh	= 0;
62*7d8d8cfdSAndy Lutomirski 	regs.es		= TSS(es);
63*7d8d8cfdSAndy Lutomirski 	regs.__esh	= 0;
64*7d8d8cfdSAndy Lutomirski 	regs.ds		= TSS(ds);
65*7d8d8cfdSAndy Lutomirski 	regs.__dsh	= 0;
66*7d8d8cfdSAndy Lutomirski 	regs.ax		= TSS(ax);
67*7d8d8cfdSAndy Lutomirski 	regs.bp		= TSS(bp);
68*7d8d8cfdSAndy Lutomirski 	regs.di		= TSS(di);
69*7d8d8cfdSAndy Lutomirski 	regs.si		= TSS(si);
70*7d8d8cfdSAndy Lutomirski 	regs.dx		= TSS(dx);
71*7d8d8cfdSAndy Lutomirski 	regs.cx		= TSS(cx);
72*7d8d8cfdSAndy Lutomirski 	regs.bx		= TSS(bx);
73e99b6f46SAndy Lutomirski 
74*7d8d8cfdSAndy Lutomirski 	do_double_fault(&regs, 0, cr2);
75e99b6f46SAndy Lutomirski 
76*7d8d8cfdSAndy Lutomirski 	/*
77*7d8d8cfdSAndy Lutomirski 	 * x86_32 does not save the original CR3 anywhere on a task switch.
78*7d8d8cfdSAndy Lutomirski 	 * This means that, even if we wanted to return, we would need to find
79*7d8d8cfdSAndy Lutomirski 	 * some way to reconstruct CR3.  We could make a credible guess based
80*7d8d8cfdSAndy Lutomirski 	 * on cpu_tlbstate, but that would be racy and would not account for
81*7d8d8cfdSAndy Lutomirski 	 * PTI.
82*7d8d8cfdSAndy Lutomirski 	 *
83*7d8d8cfdSAndy Lutomirski 	 * Instead, don't bother.  We can return through
84*7d8d8cfdSAndy Lutomirski 	 * rewind_stack_do_exit() instead.
85*7d8d8cfdSAndy Lutomirski 	 */
86*7d8d8cfdSAndy Lutomirski 	panic("cannot return from double fault\n");
87e99b6f46SAndy Lutomirski }
88*7d8d8cfdSAndy Lutomirski NOKPROBE_SYMBOL(doublefault_shim);
89e99b6f46SAndy Lutomirski 
90dc4e0021SAndy Lutomirski DEFINE_PER_CPU_PAGE_ALIGNED(struct doublefault_stack, doublefault_stack) = {
91dc4e0021SAndy Lutomirski 	.tss = {
92dc4e0021SAndy Lutomirski                 /*
93dc4e0021SAndy Lutomirski                  * No sp0 or ss0 -- we never run CPL != 0 with this TSS
94dc4e0021SAndy Lutomirski                  * active.  sp is filled in later.
95dc4e0021SAndy Lutomirski                  */
96e99b6f46SAndy Lutomirski 		.ldt		= 0,
97e99b6f46SAndy Lutomirski 	.io_bitmap_base	= IO_BITMAP_OFFSET_INVALID,
98e99b6f46SAndy Lutomirski 
99*7d8d8cfdSAndy Lutomirski 		.ip		= (unsigned long) double_fault,
100*7d8d8cfdSAndy Lutomirski 		.flags		= X86_EFLAGS_FIXED,
101e99b6f46SAndy Lutomirski 		.es		= __USER_DS,
102e99b6f46SAndy Lutomirski 		.cs		= __KERNEL_CS,
103e99b6f46SAndy Lutomirski 		.ss		= __KERNEL_DS,
104e99b6f46SAndy Lutomirski 		.ds		= __USER_DS,
105e99b6f46SAndy Lutomirski 		.fs		= __KERNEL_PERCPU,
106e99b6f46SAndy Lutomirski #ifndef CONFIG_X86_32_LAZY_GS
107e99b6f46SAndy Lutomirski 		.gs		= __KERNEL_STACK_CANARY,
108e99b6f46SAndy Lutomirski #endif
109e99b6f46SAndy Lutomirski 
110e99b6f46SAndy Lutomirski 		.__cr3		= __pa_nodebug(swapper_pg_dir),
111dc4e0021SAndy Lutomirski 	},
112e99b6f46SAndy Lutomirski };
113dc4e0021SAndy Lutomirski 
114*7d8d8cfdSAndy Lutomirski static void set_df_gdt_entry(unsigned int cpu)
115*7d8d8cfdSAndy Lutomirski {
116*7d8d8cfdSAndy Lutomirski 	/* Set up doublefault TSS pointer in the GDT */
117*7d8d8cfdSAndy Lutomirski 	__set_tss_desc(cpu, GDT_ENTRY_DOUBLEFAULT_TSS,
118*7d8d8cfdSAndy Lutomirski 		       &get_cpu_entry_area(cpu)->doublefault_stack.tss);
119*7d8d8cfdSAndy Lutomirski 
120*7d8d8cfdSAndy Lutomirski }
121*7d8d8cfdSAndy Lutomirski 
122dc4e0021SAndy Lutomirski void doublefault_init_cpu_tss(void)
123dc4e0021SAndy Lutomirski {
124dc4e0021SAndy Lutomirski 	unsigned int cpu = smp_processor_id();
125dc4e0021SAndy Lutomirski 	struct cpu_entry_area *cea = get_cpu_entry_area(cpu);
126dc4e0021SAndy Lutomirski 
127dc4e0021SAndy Lutomirski 	/*
128dc4e0021SAndy Lutomirski 	 * The linker isn't smart enough to initialize percpu variables that
129dc4e0021SAndy Lutomirski 	 * point to other places in percpu space.
130dc4e0021SAndy Lutomirski 	 */
131dc4e0021SAndy Lutomirski         this_cpu_write(doublefault_stack.tss.sp,
132dc4e0021SAndy Lutomirski                        (unsigned long)&cea->doublefault_stack.stack +
133dc4e0021SAndy Lutomirski                        sizeof(doublefault_stack.stack));
134dc4e0021SAndy Lutomirski 
135*7d8d8cfdSAndy Lutomirski 	set_df_gdt_entry(cpu);
136dc4e0021SAndy Lutomirski }
137