extern u8 insn_page[], insn_page_end[];
extern u8 test_insn[], test_insn_end[];
extern u8 alt_insn_page[];
asm(
".align 4096\n\t"
".global insn_page\n\t"
".global insn_page_end\n\t"
".global test_insn\n\t"
".global test_insn_end\n\t"
"insn_page:\n\t"
"ret \n\t"
"push %rax; push %rbx\n\t"
"push %rcx; push %rdx\n\t"
"push %rsi; push %rdi\n\t"
"push %rbp\n\t"
"push %r8; push %r9\n\t"
"push %r10; push %r11\n\t"
"push %r12; push %r13\n\t"
"push %r14; push %r15\n\t"
"pushf\n\t"
"push 136+save \n\t"
"popf \n\t"
"mov 0+save, %rax \n\t"
"mov 8+save, %rbx \n\t"
"mov 16+save, %rcx \n\t"
"mov 24+save, %rdx \n\t"
"mov 32+save, %rsi \n\t"
"mov 40+save, %rdi \n\t"
"mov 56+save, %rbp \n\t"
"mov 64+save, %r8 \n\t"
"mov 72+save, %r9 \n\t"
"mov 80+save, %r10 \n\t"
"mov 88+save, %r11 \n\t"
"mov 96+save, %r12 \n\t"
"mov 104+save, %r13 \n\t"
"mov 112+save, %r14 \n\t"
"mov 120+save, %r15 \n\t"
"test_insn:\n\t"
"in (%dx),%al\n\t"
". = . + 31\n\t"
"test_insn_end:\n\t"
"pushf \n\t"
"pop 136+save \n\t"
"mov %rax, 0+save \n\t"
"mov %rbx, 8+save \n\t"
"mov %rcx, 16+save \n\t"
"mov %rdx, 24+save \n\t"
"mov %rsi, 32+save \n\t"
"mov %rdi, 40+save \n\t"
"mov %rbp, 56+save \n\t"
"mov %r8, 64+save \n\t"
"mov %r9, 72+save \n\t"
"mov %r10, 80+save \n\t"
"mov %r11, 88+save \n\t"
"mov %r12, 96+save \n\t"
"mov %r13, 104+save \n\t"
"mov %r14, 112+save \n\t"
"mov %r15, 120+save \n\t"
"popf \n\t"
"pop %r15; pop %r14 \n\t"
"pop %r13; pop %r12 \n\t"
"pop %r11; pop %r10 \n\t"
"pop %r9; pop %r8 \n\t"
"pop %rbp \n\t"
"pop %rdi; pop %rsi \n\t"
"pop %rdx; pop %rcx \n\t"
"pop %rbx; pop %rax \n\t"
"ret\n\t"
"save:\n\t"
". = . + 256\n\t"
".align 4096\n\t"
"alt_insn_page:\n\t"
". = . + 4096\n\t"
);
static void mk_insn_page(uint8_t *alt_insn_page,
uint8_t *alt_insn, int alt_insn_length)
{
int i, emul_offset;
for (i=1; i<test_insn_end - test_insn; i++)
test_insn[i] = 0x90; // nop
emul_offset = test_insn - insn_page;
for (i=0; i<alt_insn_length; i++)
alt_insn_page[i+emul_offset] = alt_insn[i];
}
static void trap_emulator(uint64_t *mem, uint8_t* alt_insn, int alt_insn_length)
{
ulong *cr3 = (ulong *)read_cr3();
int save_offset = (u8 *)(&save) - insn_page;
memset(alt_insn_page, 0x90, 4096);
save = inregs;
mk_insn_page(alt_insn_page, alt_insn, alt_insn_length);
// Load the code TLB with insn_page, but point the page tables at
// alt_insn_page (and keep the data TLB clear, for AMD decode assist).
// This will make the CPU trap on the insn_page instruction but the
// hypervisor will see alt_insn_page.
//install_page(cr3, virt_to_phys(insn_page), insn_page);
invlpg(insn_page);
// Load code TLB
asm volatile("call *%0" : : "r"(insn_page));
install_page(cr3, virt_to_phys(alt_insn_page), insn_page);
// Trap, let hypervisor emulate at alt_insn_page
asm volatile("call *%0": : "r"(insn_page+1));
outregs = *((struct regs *)(&alt_insn_page[save_offset]));
}
static void test_movabs(uint64_t *mem)
{
// mov $0xc3c3c3c3c3c3c3c3, %rcx
uint8_t alt_insn[] = {0x48, 0xb9, 0xc3, 0xc3, 0xc3,
0xc3, 0xc3, 0xc3, 0xc3, 0xc3};
inregs = (struct regs){ 0 };
trap_emulator(mem, alt_insn, 10);
report("64-bit mov imm2", outregs.rcx == 0xc3c3c3c3c3c3c3c3);
}
On Wed, Jun 19, 2013 at 12:09 AM, Gleb Natapov <gleb@xxxxxxxxxx> wrote:
> On Tue, Jun 18, 2013 at 11:56:24PM +0800, 李春奇 <Arthur Chunqi Li> wrote:
>> On Tue, Jun 18, 2013 at 11:47 PM, Gleb Natapov <gleb@xxxxxxxxxx> wrote:
>> > On Tue, Jun 18, 2013 at 10:28:59PM +0800, Ê??Ê?•Â•? <Arthur Chunqi Li> wrote:
>> >> On Tue, Jun 18, 2013 at 8:45 PM, Gleb Natapov <gleb@xxxxxxxxxx> wrote:
>> >> > On Thu, Jun 13, 2013 at 05:30:03PM +0800, 李春奇 <Arthur Chunqi Li> wrote:
>> >> >> Hi Gleb,
>> >> >> I'm trying to solve these problems in the past days and meet many
>> >> >> difficulties. You want to save all the general registers in calling
>> >> >> insn_page, so registers should be saved to (save) in insn_page.
>> >> >> Because all the instructions should be generated outside and copy to
>> >> >> insn_page, and the instructions generated outside is RIP-relative, so
>> >> >> inside insn_page (save) will be wrong pointed with RIP-relative code.
>> >> >>
>> >> > They do not have to be generated outside. You can write code into
>> >> > insn_page directly. Something like this outside of any functions:
>> >> >
>> >> > asm(".align 4096\n\t"
>> >> > ".global insn_page\n\t"
>> >> > ".global insn_page_end\n\t"
>> >> > ".global test_insn\n\t"
>> >> > ".global test_insn_end\n\t"
>> >> > "insn_page:"
>> >> > "mov %%rax, outregs \n\t"
>> >> > ...
>> >> > "test_insn:\n\t"
>> >> > "in (%ds), %al\n\t"
>> >> > ". = . + 31\n\t"
>> >> > "test_insn_end:\n\t"
>> >> > "mov outregs, %%rax\n\t"
>> >> > ...
>> >> > "ret\n\t"
>> >> > ".align 4096\n\t"
>> >> > "insn_page_end:\n\t");
>> >> >
>> >> > Now you copy that into alt_insn_page, put instruction you want to test
>> >> > into test_insn offset and remap alt_insn_page into "insn_page" virtual address.
>> >> I used such codes:
>> >>
>> >> invlpg((void *)virt_to_phys(insn_page));
>> > virt_to_phys?
>> This is a mistake, I changed it to "invlpg(insn_page)" but the result
>> is the same.
>> >
>> >> asm volatile("call *%0" : : "r"(insn_page));
>> >> install_page(cr3, virt_to_phys(alt_insn_page), insn_page);
>> >> asm volatile("call *%0": : "r"(insn_page+1));
>> > +1?
>> Here I put "ret" on the first byte of insn_page, so the first call of
>> "insn_page" can just return, and the second call of "insn_page+1“ will
>> directly call the second byte, which is the real content of insn_page.
> Send the code.
>
> --
> Gleb.
--
Arthur Chunqi Li
Department of Computer Science
School of EECS
Peking University
Beijing, China
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