1 /* SPDX-License-Identifier: GPL-2.0 */ 2 #include <linux/kernel.h> 3 4 #include <asm/desc.h> 5 #include <asm/fred.h> 6 #include <asm/tlbflush.h> 7 #include <asm/traps.h> 8 9 /* #DB in the kernel would imply the use of a kernel debugger. */ 10 #define FRED_DB_STACK_LEVEL 1UL 11 #define FRED_NMI_STACK_LEVEL 2UL 12 #define FRED_MC_STACK_LEVEL 2UL 13 /* 14 * #DF is the highest level because a #DF means "something went wrong 15 * *while delivering an exception*." The number of cases for which that 16 * can happen with FRED is drastically reduced and basically amounts to 17 * "the stack you pointed me to is broken." Thus, always change stacks 18 * on #DF, which means it should be at the highest level. 19 */ 20 #define FRED_DF_STACK_LEVEL 3UL 21 22 #define FRED_STKLVL(vector, lvl) ((lvl) << (2 * (vector))) 23 24 DEFINE_PER_CPU(unsigned long, fred_rsp0); 25 EXPORT_PER_CPU_SYMBOL(fred_rsp0); 26 27 void cpu_init_fred_exceptions(void) 28 { 29 /* When FRED is enabled by default, remove this log message */ 30 pr_info("Initialize FRED on CPU%d\n", smp_processor_id()); 31 32 /* 33 * If a kernel event is delivered before a CPU goes to user level for 34 * the first time, its SS is NULL thus NULL is pushed into the SS field 35 * of the FRED stack frame. But before ERETS is executed, the CPU may 36 * context switch to another task and go to user level. Then when the 37 * CPU comes back to kernel mode, SS is changed to __KERNEL_DS. Later 38 * when ERETS is executed to return from the kernel event handler, a #GP 39 * fault is generated because SS doesn't match the SS saved in the FRED 40 * stack frame. 41 * 42 * Initialize SS to __KERNEL_DS when enabling FRED to avoid such #GPs. 43 */ 44 loadsegment(ss, __KERNEL_DS); 45 46 wrmsrl(MSR_IA32_FRED_CONFIG, 47 /* Reserve for CALL emulation */ 48 FRED_CONFIG_REDZONE | 49 FRED_CONFIG_INT_STKLVL(0) | 50 FRED_CONFIG_ENTRYPOINT(asm_fred_entrypoint_user)); 51 52 wrmsrl(MSR_IA32_FRED_STKLVLS, 0); 53 wrmsrl(MSR_IA32_FRED_RSP0, 0); 54 wrmsrl(MSR_IA32_FRED_RSP1, 0); 55 wrmsrl(MSR_IA32_FRED_RSP2, 0); 56 wrmsrl(MSR_IA32_FRED_RSP3, 0); 57 58 /* Enable FRED */ 59 cr4_set_bits(X86_CR4_FRED); 60 /* Any further IDT use is a bug */ 61 idt_invalidate(); 62 63 /* Use int $0x80 for 32-bit system calls in FRED mode */ 64 setup_clear_cpu_cap(X86_FEATURE_SYSENTER32); 65 setup_clear_cpu_cap(X86_FEATURE_SYSCALL32); 66 } 67 68 /* Must be called after setup_cpu_entry_areas() */ 69 void cpu_init_fred_rsps(void) 70 { 71 /* 72 * The purpose of separate stacks for NMI, #DB and #MC *in the kernel* 73 * (remember that user space faults are always taken on stack level 0) 74 * is to avoid overflowing the kernel stack. 75 */ 76 wrmsrl(MSR_IA32_FRED_STKLVLS, 77 FRED_STKLVL(X86_TRAP_DB, FRED_DB_STACK_LEVEL) | 78 FRED_STKLVL(X86_TRAP_NMI, FRED_NMI_STACK_LEVEL) | 79 FRED_STKLVL(X86_TRAP_MC, FRED_MC_STACK_LEVEL) | 80 FRED_STKLVL(X86_TRAP_DF, FRED_DF_STACK_LEVEL)); 81 82 /* The FRED equivalents to IST stacks... */ 83 wrmsrl(MSR_IA32_FRED_RSP1, __this_cpu_ist_top_va(DB)); 84 wrmsrl(MSR_IA32_FRED_RSP2, __this_cpu_ist_top_va(NMI)); 85 wrmsrl(MSR_IA32_FRED_RSP3, __this_cpu_ist_top_va(DF)); 86 } 87