access.c

kvm 源代码

#include "smp.h"
#include "printf.h"

typedef unsigned long pt_element_t;

#define PAGE_SIZE ((pt_element_t)4096)
#define PAGE_MASK (~(PAGE_SIZE-1))

#define PT_BASE_ADDR_MASK ((pt_element_t)((((pt_element_t)1 << 40) - 1) & PAGE_MASK))

#define PT_PRESENT_MASK    ((pt_element_t)1 << 0)
#define PT_WRITABLE_MASK   ((pt_element_t)1 << 1)
#define PT_USER_MASK       ((pt_element_t)1 << 2)
#define PT_ACCESSED_MASK   ((pt_element_t)1 << 5)
#define PT_DIRTY_MASK      ((pt_element_t)1 << 6)

#define CR0_WP_MASK (1UL << 16)

#define PFERR_PRESENT_MASK (1U << 0)
#define PFERR_WRITE_MASK (1U << 1)
#define PFERR_USER_MASK (1U << 2)

/*
 * page table access check tests
 */

enum {
    AC_PTE_PRESENT,
    AC_PTE_WRITABLE,
    AC_PTE_USER,
    AC_PTE_ACCESSED,
    AC_PTE_DIRTY,
    // AC_PTE_NX,

    AC_ACCESS_USER,
    AC_ACCESS_WRITE,
    // AC_ACCESS_FETCH,
    // AC_ACCESS_PTE,

    // AC_CPU_EFER_NX,
    AC_CPU_CR0_WP,

    NR_AC_FLAGS
};

const char *ac_names[] = {
    [AC_PTE_PRESENT] = "pte.p",
    [AC_PTE_ACCESSED] = "pte.a",
    [AC_PTE_WRITABLE] = "pte.rw",
    [AC_PTE_USER] = "pte.user",
    [AC_PTE_DIRTY] = "pte.d",
    [AC_ACCESS_WRITE] = "write",
    [AC_ACCESS_USER] = "user",
    [AC_CPU_CR0_WP] = "cr0.wp",
};

static inline void *va(pt_element_t phys)
{
    return (void *)phys;
}

static unsigned long read_cr0()
{
    unsigned long cr0;

    asm volatile ("mov %%cr0, %0" : "=r"(cr0));

    return cr0;
}

static void write_cr0(unsigned long cr0)
{
    asm volatile ("mov %0, %%cr0" : : "r"(cr0));
}

typedef struct {
    unsigned short offset0;
    unsigned short selector;
    unsigned short ist : 3;
    unsigned short : 5;
    unsigned short type : 4;
    unsigned short : 1;
    unsigned short dpl : 2;
    unsigned short p : 1;
    unsigned short offset1;
    unsigned offset2;
    unsigned reserved;
} idt_entry_t;

typedef struct {
    unsigned flags[NR_AC_FLAGS];
    void *virt;
    pt_element_t phys;
    pt_element_t pt_pool;
    pt_element_t *ptep;
    pt_element_t expected_pte;
    int expected_fault;
    unsigned expected_error;
    idt_entry_t idt[256];
} ac_test_t;

typedef struct {
    unsigned short limit;
    unsigned long linear_addr;
} __attribute__((packed)) descriptor_table_t;

void lidt(idt_entry_t *idt, int nentries)
{
    descriptor_table_t dt;
    
    dt.limit = nentries * sizeof(*idt) - 1;
    dt.linear_addr = (unsigned long)idt;
    asm volatile ("lidt %0" : : "m"(dt));
}

void memset(void *a, unsigned char v, int n)
{
    unsigned char *x = a;

    while (n--)
	*x++ = v;
}

unsigned short read_cs()
{
    unsigned short r;

    asm volatile ("mov %%cs, %0" : "=r"(r));
}

void set_idt_entry(idt_entry_t *e, void *addr, int dpl)
{
    memset(e, 0, sizeof *e);
    e->offset0 = (unsigned long)addr;
    e->selector = read_cs();
    e->ist = 0;
    e->type = 14;
    e->dpl = dpl;
    e->p = 1;
    e->offset1 = (unsigned long)addr >> 16;
    e->offset2 = (unsigned long)addr >> 32;
}

void set_cr0_wp(int wp)
{
    unsigned long cr0 = read_cr0();

    cr0 &= ~CR0_WP_MASK;
    if (wp)
	cr0 |= CR0_WP_MASK;
    write_cr0(cr0);
}

void ac_test_init(ac_test_t *at)
{
    set_cr0_wp(1);
    for (int i = 0; i < NR_AC_FLAGS; ++i)
	at->flags[i] = 0;
    at->virt = (void *)(0x123400000000 + 16 * smp_id());
    at->phys = 32 * 1024 * 1024;
    at->pt_pool = 33 * 1024 * 1024;
    memset(at->idt, 0, sizeof at->idt);
    lidt(at->idt, 256);
    extern char page_fault, kernel_entry;
    set_idt_entry(&at->idt[14], &page_fault, 0);
    set_idt_entry(&at->idt[0x20], &kernel_entry, 3);
}

int ac_test_bump(ac_test_t *at)
{
    for (int i = 0; i < NR_AC_FLAGS; ++i)
	if (!at->flags[i]) {
	    at->flags[i] = 1;
	    return 1;
	} else
	    at->flags[i] = 0;
    return 0;
}

unsigned long read_cr3()
{
    unsigned long cr3;

    asm volatile ("mov %%cr3, %0" : "=r"(cr3));
    return cr3;
}

void invlpg(void *addr)
{
    asm volatile ("invlpg (%0)" : : "r"(addr));
}

pt_element_t ac_test_alloc_pt(ac_test_t *at)
{
    pt_element_t ret = at->pt_pool;
    at->pt_pool += PAGE_SIZE;
    return ret;
}

void ac_test_setup_pte(ac_test_t *at)
{
    unsigned long root = read_cr3();

    for (int i = 4; i >= 1; --i) {
	pt_element_t *vroot = va(root & PT_BASE_ADDR_MASK);
	unsigned index = ((unsigned long)at->virt >> (12 + (i-1) * 9)) & 511;
	pt_element_t pte;
	if (i != 1) {
	    pte = vroot[index];
	    if (!(pte & PT_PRESENT_MASK))
		pte = ac_test_alloc_pt(at) | PT_PRESENT_MASK;
	    pte |= PT_WRITABLE_MASK | PT_USER_MASK;
	} else {
	    pte = at->phys & PT_BASE_ADDR_MASK;
	    if (at->flags[AC_PTE_PRESENT])
		pte |= PT_PRESENT_MASK;
	    if (at->flags[AC_PTE_WRITABLE])
		pte |= PT_WRITABLE_MASK;
	    if (at->flags[AC_PTE_USER])
		pte |= PT_USER_MASK;
	    if (at->flags[AC_PTE_ACCESSED])
		pte |= PT_ACCESSED_MASK;
	    if (at->flags[AC_PTE_DIRTY])
		pte |= PT_DIRTY_MASK;
	    at->ptep = &vroot[index];
	}
	vroot[index] = pte;
	root = vroot[index];
    }
    invlpg(at->virt);
    at->expected_pte = *at->ptep;
    at->expected_fault = 0;
    at->expected_error = 0;
    if (!at->flags[AC_PTE_PRESENT])
	at->expected_fault = 1;
    else
	at->expected_error |= PFERR_PRESENT_MASK;

    if (at->flags[AC_ACCESS_USER]) {
	at->expected_error |= PFERR_USER_MASK;
	if (!at->flags[AC_PTE_USER])
	    at->expected_fault = 1;
    }

    if (at->flags[AC_ACCESS_WRITE]) {
	at->expected_error |= PFERR_WRITE_MASK;
	if (!at->flags[AC_PTE_WRITABLE]
	    && (at->flags[AC_CPU_CR0_WP] || at->flags[AC_ACCESS_USER])) {
	    at->expected_fault = 1;
	} else if (!at->expected_fault) {
	    at->expected_pte |= PT_DIRTY_MASK;
	}
    }

    if (!at->expected_fault) {
	at->expected_pte |= PT_ACCESSED_MASK;
    }
}

int ac_test_do_access(ac_test_t *at)
{
    static unsigned unique = 42;
    int fault = 0;
    unsigned e;
    static unsigned char user_stack[4096];
    unsigned long rsp;

    ++unique;

    unsigned r = unique;
    set_cr0_wp(at->flags[AC_CPU_CR0_WP]);
    asm volatile ("mov %%rsp, %%rdx \n\t"
		  "cmp $0, %[user] \n\t"
		  "jz do_access \n\t"
		  "push %%rax; mov %[user_ds], %%ax; mov %%ax, %%ds; pop %%rax  \n\t"
		  "pushq %[user_ds] \n\t"
		  "pushq %[user_stack_top] \n\t"
		  "pushfq \n\t"
		  "pushq %[user_cs] \n\t"
		  "pushq $do_access \n\t"
		  "iretq \n"
		  "do_access: \n\t"
		  "cmp $0, %[write] \n\t"
		  "jnz 1f \n\t"
		  "mov (%[addr]), %[reg] \n\t"
		  "jmp done \n\t"
		  "1: mov %[reg], (%[addr]) \n\t"
		  "done: \n"
		  "fixed1: \n"
		  "int %[kernel_entry_vector] \n\t"
		  "back_to_kernel:"
		  : [reg]"+r"(r), "+a"(fault), "=b"(e), "=&d"(rsp)
		  : [addr]"r"(at->virt),
		    [write]"r"(at->flags[AC_ACCESS_WRITE]),
		    [user]"r"(at->flags[AC_ACCESS_USER]),
		    [user_ds]"i"(32+3),
		    [user_cs]"i"(24+3),
		    [user_stack_top]"r"(user_stack + sizeof user_stack),
		    [kernel_entry_vector]"i"(0x20));

    asm volatile (".section .text.pf \n\t"
		  "page_fault: \n\t"
		  "pop %rbx \n\t"
		  "movq $fixed1, (%rsp) \n\t"
		  "movl $1, %eax \n\t"
		  "iretq \n\t"
		  ".section .text");

    asm volatile (".section .text.entry \n\t"
		  "kernel_entry: \n\t"
		  "mov %rdx, %rsp \n\t"
		  "jmp back_to_kernel \n\t"
		  ".section .text");

    if (fault && !at->expected_fault) {
	printf("unexpected fault\n");
	return 0;
    }
    if (!fault && at->expected_fault) {
	printf("unexpected access\n");
	return 0;
    }
    if (fault && e != at->expected_error) {
	printf("error code %x expected %x\n", e, at->expected_fault);
	return 0;
    }
    if (*at->ptep != at->expected_pte) {
	printf("pte %x expected %x\n", *at->ptep, at->expected_pte);
	return 0;
    }

    printf("OK\n");
    return 1;
}

void ac_test_exec(ac_test_t *at)
{
    int r;

    printf("test");
    for (int i = 0; i < NR_AC_FLAGS; ++i)
	if (at->flags[i])
	    printf(" %s", ac_names[i]);
    printf(": ");
    ac_test_setup_pte(at);
    r = ac_test_do_access(at);
}

void ac_test_run()
{
    static ac_test_t at;

    printf("run\n");
    ac_test_init(&at);
    do {
	ac_test_exec(&at);
    } while (ac_test_bump(&at));
}

int main()
{
    printf("starting test\n\n");
    smp_init(ac_test_run);
    ac_test_run();
    return 0;
}