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.
I have tried to move (save) into insn_page. But when calling
insn_page, data in it can only be read and any instructions like "xchg
%%rax, 0+%[save]" may cause error, because at this time read is from
TLB but write will cause inconsistent.
Another way is disabling RIP-relative code, but I failed when using
"-mcmodel-large -fno-pic", the binary is also using RIP-relative mode.
Is there any way to totally disable RIP-relative code? Besides, using
this feature may specified to some newer C compiler. This may not be a
good solution.
If we don't set %rsp and %rbp when executing emulator code, we can
just use “push/pop" to save other general registers.
If you have any better solutions, please let me know.
Thanks,
Arthur
On Thu, Jun 13, 2013 at 12:50 PM, 李春奇 <Arthur Chunqi Li>
<yzt356@xxxxxxxxx> wrote:
> On Thu, Jun 13, 2013 at 4:50 AM, Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote:
>> Il 06/06/2013 11:24, Arthur Chunqi Li ha scritto:
>>> Add a function trap_emulator to run an instruction in emulator.
>>> Set inregs first (%rax is invalid because it is used as return
>>> address), put instruction codec in alt_insn and call func with
>>> alt_insn_length. Get results in outregs.
>>>
>>> Signed-off-by: Arthur Chunqi Li <yzt356@xxxxxxxxx>
>>> ---
>>> x86/emulator.c | 81 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>>> 1 file changed, 81 insertions(+)
>>>
>>> diff --git a/x86/emulator.c b/x86/emulator.c
>>> index 96576e5..8ab9904 100644
>>> --- a/x86/emulator.c
>>> +++ b/x86/emulator.c
>>> @@ -11,6 +11,14 @@ int fails, tests;
>>>
>>> static int exceptions;
>>>
>>> +struct regs {
>>> + u64 rax, rbx, rcx, rdx;
>>> + u64 rsi, rdi, rsp, rbp;
>>> + u64 rip, rflags;
>>> +};
>>> +
>>> +static struct regs inregs, outregs;
>>> +
>>> void report(const char *name, int result)
>>> {
>>> ++tests;
>>> @@ -685,6 +693,79 @@ static void test_shld_shrd(u32 *mem)
>>> report("shrd (cl)", *mem == ((0x12345678 >> 3) | (5u << 29)));
>>> }
>>>
>>> +static void trap_emulator(uint64_t *mem, uint8_t *insn_page,
>>> + uint8_t *alt_insn_page, void *insn_ram,
>>> + uint8_t *alt_insn, int alt_insn_length)
>>> +{
>>> + ulong *cr3 = (ulong *)read_cr3();
>>> + int i;
>>> +
>>> + // Pad with RET instructions
>>> + memset(insn_page, 0xc3, 4096);
>>> + memset(alt_insn_page, 0xc3, 4096);
>>> +
>>> + // Place a trapping instruction in the page to trigger a VMEXIT
>>> + insn_page[0] = 0x89; // mov %eax, (%rax)
>>> + insn_page[1] = 0x00;
>>> + insn_page[2] = 0x90; // nop
>>> + insn_page[3] = 0xc3; // ret
>>> +
>>> + // Place the instruction we want the hypervisor to see in the alternate page
>>> + for (i=0; i<alt_insn_length; i++)
>>> + alt_insn_page[i] = alt_insn[i];
>>> +
>>> + // Save general registers
>>> + asm volatile(
>>> + "push %rax\n\r"
>>> + "push %rbx\n\r"
>>> + "push %rcx\n\r"
>>> + "push %rdx\n\r"
>>> + "push %rsi\n\r"
>>> + "push %rdi\n\r"
>>> + );
>>
>> This will not work if GCC is using rsp-relative addresses to access
>> local variables. You need to use mov instructions to load from inregs,
>> and put the push/pop sequences inside the "main" asm that does the "call
>> *%1".
> Is there any way to let gcc use absolute address to access variables?
> I move variant "save" to the global and use "xchg %%rax, 0+%[save]"
> and it seems that addressing for "save" is wrong.
>
> Arthur
>>
>> Paolo
>>
>>> + // 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_ram);
>>> + invlpg(insn_ram);
>>> + // Load code TLB
>>> + asm volatile("call *%0" : : "r"(insn_ram + 3));
>>> + install_page(cr3, virt_to_phys(alt_insn_page), insn_ram);
>>> + // Trap, let hypervisor emulate at alt_insn_page
>>> + asm volatile(
>>> + "call *%1\n\r"
>>> +
>>> + "mov %%rax, 0+%[outregs] \n\t"
>>> + "mov %%rbx, 8+%[outregs] \n\t"
>>> + "mov %%rcx, 16+%[outregs] \n\t"
>>> + "mov %%rdx, 24+%[outregs] \n\t"
>>> + "mov %%rsi, 32+%[outregs] \n\t"
>>> + "mov %%rdi, 40+%[outregs] \n\t"
>>> + "mov %%rsp,48+ %[outregs] \n\t"
>>> + "mov %%rbp, 56+%[outregs] \n\t"
>>> +
>>> + /* Save RFLAGS in outregs*/
>>> + "pushf \n\t"
>>> + "popq 72+%[outregs] \n\t"
>>> + : [outregs]"+m"(outregs)
>>> + : "r"(insn_ram),
>>> + "a"(mem), "b"(inregs.rbx),
>>> + "c"(inregs.rcx), "d"(inregs.rdx),
>>> + "S"(inregs.rsi), "D"(inregs.rdi)
>>> + : "memory", "cc"
>>> + );
>>> + // Restore general registers
>>> + asm volatile(
>>> + "pop %rax\n\r"
>>> + "pop %rbx\n\r"
>>> + "pop %rcx\n\r"
>>> + "pop %rdx\n\r"
>>> + "pop %rsi\n\r"
>>> + "pop %rdi\n\r"
>>> + );
>>> +}
>>> +
>>> static void advance_rip_by_3_and_note_exception(struct ex_regs *regs)
>>> {
>>> ++exceptions;
>>>
>>
>
>
>
> --
> Arthur Chunqi Li
> Department of Computer Science
> School of EECS
> Peking University
> Beijing, China
--
Arthur Chunqi Li
Department of Computer Science
School of EECS
Peking University
Beijing, China
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