diff options
Diffstat (limited to 'arch/x86/realmode/rm/trampoline_64.S')
| -rw-r--r-- | arch/x86/realmode/rm/trampoline_64.S | 246 |
1 files changed, 246 insertions, 0 deletions
diff --git a/arch/x86/realmode/rm/trampoline_64.S b/arch/x86/realmode/rm/trampoline_64.S new file mode 100644 index 000000000..e38d61d65 --- /dev/null +++ b/arch/x86/realmode/rm/trampoline_64.S @@ -0,0 +1,246 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +/* + * + * Trampoline.S Derived from Setup.S by Linus Torvalds + * + * 4 Jan 1997 Michael Chastain: changed to gnu as. + * 15 Sept 2005 Eric Biederman: 64bit PIC support + * + * Entry: CS:IP point to the start of our code, we are + * in real mode with no stack, but the rest of the + * trampoline page to make our stack and everything else + * is a mystery. + * + * On entry to trampoline_start, the processor is in real mode + * with 16-bit addressing and 16-bit data. CS has some value + * and IP is zero. Thus, data addresses need to be absolute + * (no relocation) and are taken with regard to r_base. + * + * With the addition of trampoline_level4_pgt this code can + * now enter a 64bit kernel that lives at arbitrary 64bit + * physical addresses. + * + * If you work on this file, check the object module with objdump + * --full-contents --reloc to make sure there are no relocation + * entries. + */ + +#include <linux/linkage.h> +#include <asm/pgtable_types.h> +#include <asm/page_types.h> +#include <asm/msr.h> +#include <asm/segment.h> +#include <asm/processor-flags.h> +#include <asm/realmode.h> +#include "realmode.h" + + .text + .code16 + + .balign PAGE_SIZE +SYM_CODE_START(trampoline_start) + cli # We should be safe anyway + wbinvd + + LJMPW_RM(1f) +1: + mov %cs, %ax # Code and data in the same place + mov %ax, %ds + mov %ax, %es + mov %ax, %ss + + # Setup stack + movl $rm_stack_end, %esp + + call verify_cpu # Verify the cpu supports long mode + testl %eax, %eax # Check for return code + jnz no_longmode + +.Lswitch_to_protected: + /* + * GDT tables in non default location kernel can be beyond 16MB and + * lgdt will not be able to load the address as in real mode default + * operand size is 16bit. Use lgdtl instead to force operand size + * to 32 bit. + */ + + lidtl tr_idt # load idt with 0, 0 + lgdtl tr_gdt # load gdt with whatever is appropriate + + movw $__KERNEL_DS, %dx # Data segment descriptor + + # Enable protected mode + movl $(CR0_STATE & ~X86_CR0_PG), %eax + movl %eax, %cr0 # into protected mode + + # flush prefetch and jump to startup_32 + ljmpl $__KERNEL32_CS, $pa_startup_32 + +no_longmode: + hlt + jmp no_longmode +SYM_CODE_END(trampoline_start) + +#ifdef CONFIG_AMD_MEM_ENCRYPT +/* SEV-ES supports non-zero IP for entry points - no alignment needed */ +SYM_CODE_START(sev_es_trampoline_start) + cli # We should be safe anyway + + LJMPW_RM(1f) +1: + mov %cs, %ax # Code and data in the same place + mov %ax, %ds + mov %ax, %es + mov %ax, %ss + + # Setup stack + movl $rm_stack_end, %esp + + jmp .Lswitch_to_protected +SYM_CODE_END(sev_es_trampoline_start) +#endif /* CONFIG_AMD_MEM_ENCRYPT */ + +#include "../kernel/verify_cpu.S" + + .section ".text32","ax" + .code32 + .balign 4 +SYM_CODE_START(startup_32) + movl %edx, %ss + addl $pa_real_mode_base, %esp + movl %edx, %ds + movl %edx, %es + movl %edx, %fs + movl %edx, %gs + + /* + * Check for memory encryption support. This is a safety net in + * case BIOS hasn't done the necessary step of setting the bit in + * the MSR for this AP. If SME is active and we've gotten this far + * then it is safe for us to set the MSR bit and continue. If we + * don't we'll eventually crash trying to execute encrypted + * instructions. + */ + btl $TH_FLAGS_SME_ACTIVE_BIT, pa_tr_flags + jnc .Ldone + movl $MSR_AMD64_SYSCFG, %ecx + rdmsr + bts $MSR_AMD64_SYSCFG_MEM_ENCRYPT_BIT, %eax + jc .Ldone + + /* + * Memory encryption is enabled but the SME enable bit for this + * CPU has has not been set. It is safe to set it, so do so. + */ + wrmsr +.Ldone: + + movl pa_tr_cr4, %eax + movl %eax, %cr4 # Enable PAE mode + + # Setup trampoline 4 level pagetables + movl $pa_trampoline_pgd, %eax + movl %eax, %cr3 + + # Set up EFER + movl $MSR_EFER, %ecx + rdmsr + /* + * Skip writing to EFER if the register already has desired + * value (to avoid #VE for the TDX guest). + */ + cmp pa_tr_efer, %eax + jne .Lwrite_efer + cmp pa_tr_efer + 4, %edx + je .Ldone_efer +.Lwrite_efer: + movl pa_tr_efer, %eax + movl pa_tr_efer + 4, %edx + wrmsr + +.Ldone_efer: + # Enable paging and in turn activate Long Mode. + movl $CR0_STATE, %eax + movl %eax, %cr0 + + /* + * At this point we're in long mode but in 32bit compatibility mode + * with EFER.LME = 1, CS.L = 0, CS.D = 1 (and in turn + * EFER.LMA = 1). Now we want to jump in 64bit mode, to do that we use + * the new gdt/idt that has __KERNEL_CS with CS.L = 1. + */ + ljmpl $__KERNEL_CS, $pa_startup_64 +SYM_CODE_END(startup_32) + +SYM_CODE_START(pa_trampoline_compat) + /* + * In compatibility mode. Prep ESP and DX for startup_32, then disable + * paging and complete the switch to legacy 32-bit mode. + */ + movl $rm_stack_end, %esp + movw $__KERNEL_DS, %dx + + movl $(CR0_STATE & ~X86_CR0_PG), %eax + movl %eax, %cr0 + ljmpl $__KERNEL32_CS, $pa_startup_32 +SYM_CODE_END(pa_trampoline_compat) + + .section ".text64","ax" + .code64 + .balign 4 +SYM_CODE_START(startup_64) + # Now jump into the kernel using virtual addresses + jmpq *tr_start(%rip) +SYM_CODE_END(startup_64) + +SYM_CODE_START(trampoline_start64) + /* + * APs start here on a direct transfer from 64-bit BIOS with identity + * mapped page tables. Load the kernel's GDT in order to gear down to + * 32-bit mode (to handle 4-level vs. 5-level paging), and to (re)load + * segment registers. Load the zero IDT so any fault triggers a + * shutdown instead of jumping back into BIOS. + */ + lidt tr_idt(%rip) + lgdt tr_gdt64(%rip) + + ljmpl *tr_compat(%rip) +SYM_CODE_END(trampoline_start64) + + .section ".rodata","a" + # Duplicate the global descriptor table + # so the kernel can live anywhere + .balign 16 +SYM_DATA_START(tr_gdt) + .short tr_gdt_end - tr_gdt - 1 # gdt limit + .long pa_tr_gdt + .short 0 + .quad 0x00cf9b000000ffff # __KERNEL32_CS + .quad 0x00af9b000000ffff # __KERNEL_CS + .quad 0x00cf93000000ffff # __KERNEL_DS +SYM_DATA_END_LABEL(tr_gdt, SYM_L_LOCAL, tr_gdt_end) + +SYM_DATA_START(tr_gdt64) + .short tr_gdt_end - tr_gdt - 1 # gdt limit + .long pa_tr_gdt + .long 0 +SYM_DATA_END(tr_gdt64) + +SYM_DATA_START(tr_compat) + .long pa_trampoline_compat + .short __KERNEL32_CS +SYM_DATA_END(tr_compat) + + .bss + .balign PAGE_SIZE +SYM_DATA(trampoline_pgd, .space PAGE_SIZE) + + .balign 8 +SYM_DATA_START(trampoline_header) + SYM_DATA_LOCAL(tr_start, .space 8) + SYM_DATA(tr_efer, .space 8) + SYM_DATA(tr_cr4, .space 4) + SYM_DATA(tr_flags, .space 4) +SYM_DATA_END(trampoline_header) + +#include "trampoline_common.S" |