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linux_dsm_epyc7002/arch/x86/kernel/head_64.S
Dave Hansen 430d4005b8 x86/mm: Comment _PAGE_GLOBAL mystery 
I was mystified as to where the _PAGE_GLOBAL in the kernel page tables
for kernel text came from.  I audited all the places I could find, but
I missed one: head_64.S.

The page tables that we create in here live for a long time, and they
also have _PAGE_GLOBAL set, despite whether the processor supports it
or not.  It's harmless, and we got *lucky* that the pageattr code
accidentally clears it when we wipe it out of __supported_pte_mask and
then later try to mark kernel text read-only.

Comment some of these properties to make it easier to find and
understand in the future.

Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Kees Cook <keescook@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Nadav Amit <namit@vmware.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-mm@kvack.org
Link: http://lkml.kernel.org/r/20180406205513.079BB265@viggo.jf.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-04-12 09:05:58 +02:00

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/* SPDX-License-Identifier: GPL-2.0 */
/*
* linux/arch/x86/kernel/head_64.S -- start in 32bit and switch to 64bit
*
* Copyright (C) 2000 Andrea Arcangeli <andrea@suse.de> SuSE
* Copyright (C) 2000 Pavel Machek <pavel@suse.cz>
* Copyright (C) 2000 Karsten Keil <kkeil@suse.de>
* Copyright (C) 2001,2002 Andi Kleen <ak@suse.de>
* Copyright (C) 2005 Eric Biederman <ebiederm@xmission.com>
*/
#include <linux/linkage.h>
#include <linux/threads.h>
#include <linux/init.h>
#include <asm/segment.h>
#include <asm/pgtable.h>
#include <asm/page.h>
#include <asm/msr.h>
#include <asm/cache.h>
#include <asm/processor-flags.h>
#include <asm/percpu.h>
#include <asm/nops.h>
#include "../entry/calling.h"
#include <asm/export.h>
#include <asm/nospec-branch.h>
#ifdef CONFIG_PARAVIRT
#include <asm/asm-offsets.h>
#include <asm/paravirt.h>
#define GET_CR2_INTO(reg) GET_CR2_INTO_RAX ; movq %rax, reg
#else
#define GET_CR2_INTO(reg) movq %cr2, reg
#define INTERRUPT_RETURN iretq
#endif
/* we are not able to switch in one step to the final KERNEL ADDRESS SPACE
* because we need identity-mapped pages.
*
*/
#define l4_index(x) (((x) >> 39) & 511)
#define pud_index(x) (((x) >> PUD_SHIFT) & (PTRS_PER_PUD-1))
L4_PAGE_OFFSET = l4_index(__PAGE_OFFSET_BASE_L4)
L4_START_KERNEL = l4_index(__START_KERNEL_map)
L3_START_KERNEL = pud_index(__START_KERNEL_map)
.text
__HEAD
.code64
.globl startup_64
startup_64:
UNWIND_HINT_EMPTY
/*
* At this point the CPU runs in 64bit mode CS.L = 1 CS.D = 0,
* and someone has loaded an identity mapped page table
* for us. These identity mapped page tables map all of the
* kernel pages and possibly all of memory.
*
* %rsi holds a physical pointer to real_mode_data.
*
* We come here either directly from a 64bit bootloader, or from
* arch/x86/boot/compressed/head_64.S.
*
* We only come here initially at boot nothing else comes here.
*
* Since we may be loaded at an address different from what we were
* compiled to run at we first fixup the physical addresses in our page
* tables and then reload them.
*/
/* Set up the stack for verify_cpu(), similar to initial_stack below */
leaq (__end_init_task - SIZEOF_PTREGS)(%rip), %rsp
/* Sanitize CPU configuration */
call verify_cpu
/*
* Perform pagetable fixups. Additionally, if SME is active, encrypt
* the kernel and retrieve the modifier (SME encryption mask if SME
* is active) to be added to the initial pgdir entry that will be
* programmed into CR3.
*/
leaq _text(%rip), %rdi
pushq %rsi
call __startup_64
popq %rsi
/* Form the CR3 value being sure to include the CR3 modifier */
addq $(early_top_pgt - __START_KERNEL_map), %rax
jmp 1f
ENTRY(secondary_startup_64)
UNWIND_HINT_EMPTY
/*
* At this point the CPU runs in 64bit mode CS.L = 1 CS.D = 0,
* and someone has loaded a mapped page table.
*
* %rsi holds a physical pointer to real_mode_data.
*
* We come here either from startup_64 (using physical addresses)
* or from trampoline.S (using virtual addresses).
*
* Using virtual addresses from trampoline.S removes the need
* to have any identity mapped pages in the kernel page table
* after the boot processor executes this code.
*/
/* Sanitize CPU configuration */
call verify_cpu
/*
* Retrieve the modifier (SME encryption mask if SME is active) to be
* added to the initial pgdir entry that will be programmed into CR3.
*/
pushq %rsi
call __startup_secondary_64
popq %rsi
/* Form the CR3 value being sure to include the CR3 modifier */
addq $(init_top_pgt - __START_KERNEL_map), %rax
1:
/* Enable PAE mode, PGE and LA57 */
movl $(X86_CR4_PAE | X86_CR4_PGE), %ecx
#ifdef CONFIG_X86_5LEVEL
testl $1, __pgtable_l5_enabled(%rip)
jz 1f
orl $X86_CR4_LA57, %ecx
1:
#endif
movq %rcx, %cr4
/* Setup early boot stage 4-/5-level pagetables. */
addq phys_base(%rip), %rax
movq %rax, %cr3
/* Ensure I am executing from virtual addresses */
movq $1f, %rax
ANNOTATE_RETPOLINE_SAFE
jmp *%rax
1:
UNWIND_HINT_EMPTY
/* Check if nx is implemented */
movl $0x80000001, %eax
cpuid
movl %edx,%edi
/* Setup EFER (Extended Feature Enable Register) */
movl $MSR_EFER, %ecx
rdmsr
btsl $_EFER_SCE, %eax /* Enable System Call */
btl $20,%edi /* No Execute supported? */
jnc 1f
btsl $_EFER_NX, %eax
btsq $_PAGE_BIT_NX,early_pmd_flags(%rip)
1: wrmsr /* Make changes effective */
/* Setup cr0 */
movl $CR0_STATE, %eax
/* Make changes effective */
movq %rax, %cr0
/* Setup a boot time stack */
movq initial_stack(%rip), %rsp
/* zero EFLAGS after setting rsp */
pushq $0
popfq
/*
* We must switch to a new descriptor in kernel space for the GDT
* because soon the kernel won't have access anymore to the userspace
* addresses where we're currently running on. We have to do that here
* because in 32bit we couldn't load a 64bit linear address.
*/
lgdt early_gdt_descr(%rip)
/* set up data segments */
xorl %eax,%eax
movl %eax,%ds
movl %eax,%ss
movl %eax,%es
/*
* We don't really need to load %fs or %gs, but load them anyway
* to kill any stale realmode selectors. This allows execution
* under VT hardware.
*/
movl %eax,%fs
movl %eax,%gs
/* Set up %gs.
*
* The base of %gs always points to the bottom of the irqstack
* union. If the stack protector canary is enabled, it is
* located at %gs:40. Note that, on SMP, the boot cpu uses
* init data section till per cpu areas are set up.
*/
movl $MSR_GS_BASE,%ecx
movl initial_gs(%rip),%eax
movl initial_gs+4(%rip),%edx
wrmsr
/* rsi is pointer to real mode structure with interesting info.
pass it to C */
movq %rsi, %rdi
.Ljump_to_C_code:
/*
* Jump to run C code and to be on a real kernel address.
* Since we are running on identity-mapped space we have to jump
* to the full 64bit address, this is only possible as indirect
* jump. In addition we need to ensure %cs is set so we make this
* a far return.
*
* Note: do not change to far jump indirect with 64bit offset.
*
* AMD does not support far jump indirect with 64bit offset.
* AMD64 Architecture Programmer's Manual, Volume 3: states only
* JMP FAR mem16:16 FF /5 Far jump indirect,
* with the target specified by a far pointer in memory.
* JMP FAR mem16:32 FF /5 Far jump indirect,
* with the target specified by a far pointer in memory.
*
* Intel64 does support 64bit offset.
* Software Developer Manual Vol 2: states:
* FF /5 JMP m16:16 Jump far, absolute indirect,
* address given in m16:16
* FF /5 JMP m16:32 Jump far, absolute indirect,
* address given in m16:32.
* REX.W + FF /5 JMP m16:64 Jump far, absolute indirect,
* address given in m16:64.
*/
pushq $.Lafter_lret # put return address on stack for unwinder
xorq %rbp, %rbp # clear frame pointer
movq initial_code(%rip), %rax
pushq $__KERNEL_CS # set correct cs
pushq %rax # target address in negative space
lretq
.Lafter_lret:
END(secondary_startup_64)
#include "verify_cpu.S"
#ifdef CONFIG_HOTPLUG_CPU
/*
* Boot CPU0 entry point. It's called from play_dead(). Everything has been set
* up already except stack. We just set up stack here. Then call
* start_secondary() via .Ljump_to_C_code.
*/
ENTRY(start_cpu0)
movq initial_stack(%rip), %rsp
UNWIND_HINT_EMPTY
jmp .Ljump_to_C_code
ENDPROC(start_cpu0)
#endif
/* Both SMP bootup and ACPI suspend change these variables */
__REFDATA
.balign 8
GLOBAL(initial_code)
.quad x86_64_start_kernel
GLOBAL(initial_gs)
.quad INIT_PER_CPU_VAR(irq_stack_union)
GLOBAL(initial_stack)
/*
* The SIZEOF_PTREGS gap is a convention which helps the in-kernel
* unwinder reliably detect the end of the stack.
*/
.quad init_thread_union + THREAD_SIZE - SIZEOF_PTREGS
__FINITDATA
__INIT
ENTRY(early_idt_handler_array)
i = 0
.rept NUM_EXCEPTION_VECTORS
.if ((EXCEPTION_ERRCODE_MASK >> i) & 1) == 0
UNWIND_HINT_IRET_REGS
pushq $0 # Dummy error code, to make stack frame uniform
.else
UNWIND_HINT_IRET_REGS offset=8
.endif
pushq $i # 72(%rsp) Vector number
jmp early_idt_handler_common
UNWIND_HINT_IRET_REGS
i = i + 1
.fill early_idt_handler_array + i*EARLY_IDT_HANDLER_SIZE - ., 1, 0xcc
.endr
UNWIND_HINT_IRET_REGS offset=16
END(early_idt_handler_array)
early_idt_handler_common:
/*
* The stack is the hardware frame, an error code or zero, and the
* vector number.
*/
cld
incl early_recursion_flag(%rip)
/* The vector number is currently in the pt_regs->di slot. */
pushq %rsi /* pt_regs->si */
movq 8(%rsp), %rsi /* RSI = vector number */
movq %rdi, 8(%rsp) /* pt_regs->di = RDI */
pushq %rdx /* pt_regs->dx */
pushq %rcx /* pt_regs->cx */
pushq %rax /* pt_regs->ax */
pushq %r8 /* pt_regs->r8 */
pushq %r9 /* pt_regs->r9 */
pushq %r10 /* pt_regs->r10 */
pushq %r11 /* pt_regs->r11 */
pushq %rbx /* pt_regs->bx */
pushq %rbp /* pt_regs->bp */
pushq %r12 /* pt_regs->r12 */
pushq %r13 /* pt_regs->r13 */
pushq %r14 /* pt_regs->r14 */
pushq %r15 /* pt_regs->r15 */
UNWIND_HINT_REGS
cmpq $14,%rsi /* Page fault? */
jnz 10f
GET_CR2_INTO(%rdi) /* Can clobber any volatile register if pv */
call early_make_pgtable
andl %eax,%eax
jz 20f /* All good */
10:
movq %rsp,%rdi /* RDI = pt_regs; RSI is already trapnr */
call early_fixup_exception
20:
decl early_recursion_flag(%rip)
jmp restore_regs_and_return_to_kernel
END(early_idt_handler_common)
__INITDATA
.balign 4
GLOBAL(early_recursion_flag)
.long 0
#define NEXT_PAGE(name) \
.balign PAGE_SIZE; \
GLOBAL(name)
#ifdef CONFIG_PAGE_TABLE_ISOLATION
/*
* Each PGD needs to be 8k long and 8k aligned. We do not
* ever go out to userspace with these, so we do not
* strictly *need* the second page, but this allows us to
* have a single set_pgd() implementation that does not
* need to worry about whether it has 4k or 8k to work
* with.
*
* This ensures PGDs are 8k long:
*/
#define PTI_USER_PGD_FILL 512
/* This ensures they are 8k-aligned: */
#define NEXT_PGD_PAGE(name) \
.balign 2 * PAGE_SIZE; \
GLOBAL(name)
#else
#define NEXT_PGD_PAGE(name) NEXT_PAGE(name)
#define PTI_USER_PGD_FILL 0
#endif
/* Automate the creation of 1 to 1 mapping pmd entries */
#define PMDS(START, PERM, COUNT) \
i = 0 ; \
.rept (COUNT) ; \
.quad (START) + (i << PMD_SHIFT) + (PERM) ; \
i = i + 1 ; \
.endr
__INITDATA
NEXT_PGD_PAGE(early_top_pgt)
.fill 512,8,0
.fill PTI_USER_PGD_FILL,8,0
NEXT_PAGE(early_dynamic_pgts)
.fill 512*EARLY_DYNAMIC_PAGE_TABLES,8,0
.data
#if defined(CONFIG_XEN_PV) || defined(CONFIG_XEN_PVH)
NEXT_PGD_PAGE(init_top_pgt)
.quad level3_ident_pgt - __START_KERNEL_map + _KERNPG_TABLE_NOENC
.org init_top_pgt + L4_PAGE_OFFSET*8, 0
.quad level3_ident_pgt - __START_KERNEL_map + _KERNPG_TABLE_NOENC
.org init_top_pgt + L4_START_KERNEL*8, 0
/* (2^48-(2*1024*1024*1024))/(2^39) = 511 */
.quad level3_kernel_pgt - __START_KERNEL_map + _PAGE_TABLE_NOENC
.fill PTI_USER_PGD_FILL,8,0
NEXT_PAGE(level3_ident_pgt)
.quad level2_ident_pgt - __START_KERNEL_map + _KERNPG_TABLE_NOENC
.fill 511, 8, 0
NEXT_PAGE(level2_ident_pgt)
/*
* Since I easily can, map the first 1G.
* Don't set NX because code runs from these pages.
*
* Note: This sets _PAGE_GLOBAL despite whether
* the CPU supports it or it is enabled. But,
* the CPU should ignore the bit.
*/
PMDS(0, __PAGE_KERNEL_IDENT_LARGE_EXEC, PTRS_PER_PMD)
#else
NEXT_PGD_PAGE(init_top_pgt)
.fill 512,8,0
.fill PTI_USER_PGD_FILL,8,0
#endif
#ifdef CONFIG_X86_5LEVEL
NEXT_PAGE(level4_kernel_pgt)
.fill 511,8,0
.quad level3_kernel_pgt - __START_KERNEL_map + _PAGE_TABLE_NOENC
#endif
NEXT_PAGE(level3_kernel_pgt)
.fill L3_START_KERNEL,8,0
/* (2^48-(2*1024*1024*1024)-((2^39)*511))/(2^30) = 510 */
.quad level2_kernel_pgt - __START_KERNEL_map + _KERNPG_TABLE_NOENC
.quad level2_fixmap_pgt - __START_KERNEL_map + _PAGE_TABLE_NOENC
NEXT_PAGE(level2_kernel_pgt)
/*
* 512 MB kernel mapping. We spend a full page on this pagetable
* anyway.
*
* The kernel code+data+bss must not be bigger than that.
*
* (NOTE: at +512MB starts the module area, see MODULES_VADDR.
* If you want to increase this then increase MODULES_VADDR
* too.)
*
* This table is eventually used by the kernel during normal
* runtime. Care must be taken to clear out undesired bits
* later, like _PAGE_RW or _PAGE_GLOBAL in some cases.
*/
PMDS(0, __PAGE_KERNEL_LARGE_EXEC,
KERNEL_IMAGE_SIZE/PMD_SIZE)
NEXT_PAGE(level2_fixmap_pgt)
.fill 506,8,0
.quad level1_fixmap_pgt - __START_KERNEL_map + _PAGE_TABLE_NOENC
/* 8MB reserved for vsyscalls + a 2MB hole = 4 + 1 entries */
.fill 5,8,0
NEXT_PAGE(level1_fixmap_pgt)
.fill 512,8,0
#undef PMDS
.data
.align 16
.globl early_gdt_descr
early_gdt_descr:
.word GDT_ENTRIES*8-1
early_gdt_descr_base:
.quad INIT_PER_CPU_VAR(gdt_page)
ENTRY(phys_base)
/* This must match the first entry in level2_kernel_pgt */
.quad 0x0000000000000000
EXPORT_SYMBOL(phys_base)
#include "../../x86/xen/xen-head.S"
__PAGE_ALIGNED_BSS
NEXT_PAGE(empty_zero_page)
.skip PAGE_SIZE
EXPORT_SYMBOL(empty_zero_page)
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