On Mon, Jun 10, 2013 at 09:38:32PM +0800, Arthur Chunqi Li wrote:
> 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.
>
That's far from what I meant :( As I said before inregs/outregs should
contain r[0-7] too so you cannot use then as tmp vars to save %rbp/%rsp.
My ideas is that the code to save/restore register (all the xchg
instructions) should be part of the code in insn_page/alt_insn_page.
Instead of call in the middle just put trapping instruction there on
insn_page (in (%dx),%al is a good one) padded with nops to the max
instruction length. alt_insn_page will have an instruction we want to
test at the same offset. This way you can call insn_page freely since
stack register during entry and return are unchanged, all the register
are saved and restored by the code on insn_page itself.
> Signed-off-by: Arthur Chunqi Li <yzt356@xxxxxxxxx>
> ---
> x86/emulator.c | 106 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 106 insertions(+)
>
> diff --git a/x86/emulator.c b/x86/emulator.c
> index 96576e5..a1bd92e 100644
> --- a/x86/emulator.c
> +++ b/x86/emulator.c
> @@ -11,6 +11,13 @@ 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 +692,105 @@ 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, int reserve_stack)
> +{
> + ulong *cr3 = (ulong *)read_cr3();
> + int i;
> + static struct regs save;
> +
> + // Pad with RET instructions
> + memset(insn_page, 0x90, 4096);
> + memset(alt_insn_page, 0x90, 4096);
> +
> + asm volatile(
> + "movw $1, %0\n\t"
> + : : "m"(mem)
> + : "memory"
> + );
> + // Place a trapping instruction in the page to trigger a VMEXIT
> + insn_page[0] = 0xc3; // ret
> + if (!reserve_stack)
> + {
> + insn_page[1] = 0x49; // xchg %rsp,%r9
> + insn_page[2] = 0x87;
> + insn_page[3] = 0xe1;
> + insn_page[4] = 0x49; // xchg %rbp,%r10
> + insn_page[5] = 0x87;
> + insn_page[6] = 0xea;
> + }
> + //in (%dx),%al, may change in the future
> + insn_page[7] = 0xec;
> +
> + // Place the instruction we want the hypervisor to see in the alternate page
> + for (i=7; i<alt_insn_length+7; i++)
> + alt_insn_page[i] = alt_insn[i-7];
> +
> + if (!reserve_stack)
> + {
> + insn_page[i+0] = 0x49; // xchg %rsp,%r9
> + insn_page[i+1] = 0x87;
> + insn_page[i+2] = 0xe1;
> + insn_page[i+3] = 0x49; // xchg %rbp,%r10
> + insn_page[i+4] = 0x87;
> + insn_page[i+5] = 0xea;
> + }
> + else
> + {
> + insn_page[i+0] = 0x49; // mov %rsp,%r9
> + insn_page[i+1] = 0x89;
> + insn_page[i+2] = 0xe1;
> + insn_page[i+3] = 0x49; // mov %rbp,%r10
> + insn_page[i+4] = 0x89;
> + insn_page[i+5] = 0xea;
> + }
> + insn_page[i+6] = 0xc3; // ret
> +
> + save = inregs;
> +
> + // 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));
> + install_page(cr3, virt_to_phys(alt_insn_page), insn_ram);
> + // Trap, let hypervisor emulate at alt_insn_page
> + asm volatile(
> + "push 72+%[save]; popf\n\t"
> + "mov %2, %%r8\n\t"
> + "xchg %%rax, 0+%[save] \n\t"
> + "xchg %%rbx, 8+%[save] \n\t"
> + "xchg %%rcx, 16+%[save] \n\t"
> + "xchg %%rdx, 24+%[save] \n\t"
> + "xchg %%rsi, 32+%[save] \n\t"
> + "xchg %%rdi, 40+%[save] \n\t"
> + "xchg %%r9, 48+%[save]\n\t"
> + "xchg %%r10, 56+%[save]\n\t"
> +
> + "call *%1\n\t"
> +
> + "xchg %%rax, 0+%[save] \n\t"
> + "xchg %%rbx, 8+%[save] \n\t"
> + "xchg %%rcx, 16+%[save] \n\t"
> + "xchg %%rdx, 24+%[save] \n\t"
> + "xchg %%rsi, 32+%[save] \n\t"
> + "xchg %%rdi, 40+%[save] \n\t"
> + "xchg %%r9, 48+%[save] \n\t"
> + "xchg %%r10, 56+%[save] \n\t"
> + /* Save RFLAGS in outregs*/
> + "pushf \n\t"
> + "pop 72+%[save] \n\t"
> + : [save]"+m"(save)
> + : "r"(insn_ram+1), "r"(mem)
> + : "memory", "cc", "r8", "r9", "r10"
> + );
> + outregs = save;
> +}
> +
> static void advance_rip_by_3_and_note_exception(struct ex_regs *regs)
> {
> ++exceptions;
> --
> 1.7.9.5
--
Gleb.
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