Re: [PATCH] kvm-unit-tests: Add test case for accessing bpl via modr/m

[Gleb Natapov <gleb@redhat.com>]

On Thu, Jun 06, 2013 at 02:47:49PM +0800, 李春奇 <Arthur Chunqi Li> wrote:
> On Thu, Jun 6, 2013 at 1:45 PM, Gleb Natapov <gleb@redhat.com> wrote:
> > On Thu, Jun 06, 2013 at 01:03:44PM +0800, Arthur Chunqi Li wrote:
> >> Test access to %bpl via modr/m addressing mode. This case can test another bug in the boot of RHEL5.9 64-bit.
> >>
> > We have growing number of instructions tests using the same tlb trick. I
> > think it is time to make the code more generic. Create a function that
> > receives instruction to check and all the tlb games will be done by that
> > function.
> Should I do some work to merge all these test cases?
> 
It would be nice, yes. I also have an idea on how to improve test
reliability. Since it relies on tlb to be out of sync with actual page
table a vmexit in a wrong time can break this assumption and wrong
instruction will be emulated (the one from insn_page instead of
alt_insn_page). If we make the instruction on insn_page place special
value somewhere and check it after the test we can see if the wrong
instruction was executed and rerun the test.

> >
> >> Signed-off-by: Arthur Chunqi Li <yzt356@gmail.com>
> >> ---
> >>  x86/emulator.c |   41 +++++++++++++++++++++++++++++++++++++++++
> >>  1 file changed, 41 insertions(+)
> >>
> >> diff --git a/x86/emulator.c b/x86/emulator.c
> >> index 96576e5..3563971 100644
> >> --- a/x86/emulator.c
> >> +++ b/x86/emulator.c
> >> @@ -901,6 +901,45 @@ static void test_simplealu(u32 *mem)
> >>      report("test", *mem == 0x8400);
> >>  }
> >>
> >> +static void test_bpl_modrm(uint64_t *mem, uint8_t *insn_page,
> >> +                       uint8_t *alt_insn_page, void *insn_ram)
> >> +{
> >> +     ulong *cr3 = (ulong *)read_cr3();
> >> +     uint16_t cx = 0;
> >> +
> >> +     // 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] = 0x66; // mov $0x4321, %cx
> >> +     insn_page[1] = 0xb9;
> >> +     insn_page[2] = 0x21;
> >> +     insn_page[3] = 0x43;
> >> +     insn_page[4] = 0x89; // mov %eax, (%rax)
> >> +     insn_page[5] = 0x00;
> >> +     insn_page[6] = 0x90; // nop
> >> +     // Place mov %cl, %bpl in alt_insn_page for emulator to execuate
> >> +     // If emulator mistaken addressing %bpl, %cl may be moved to %ch
> >> +     // %cx will be broken to 0x2121, not 0x4321
> >> +     alt_insn_page[4] = 0x40;
> >> +     alt_insn_page[5] = 0x88;
> >> +     alt_insn_page[6] = 0xcd;
> >> +
> >> +     // 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);
> >> +     // Load code TLB
> >> +     invlpg(insn_ram);
> >> +     asm volatile("call *%0" : : "r"(insn_ram+3));
> >> +     // Trap, let hypervisor emulate at alt_insn_page
> >> +     install_page(cr3, virt_to_phys(alt_insn_page), insn_ram);
> >> +     asm volatile("call *%0" : : "r"(insn_ram), "a"(mem));
> >> +     asm volatile("":"=c"(cx));
> > Why not add the constrain to previous asm?
> I will merge them in next version.
> 
> >
> >> +     report("access bpl in modr/m", cx == 0x4321);
> >> +}
> >> +
> >>  int main()
> >>  {
> >>       void *mem;
> >> @@ -964,6 +1003,8 @@ int main()
> >>
> >>       test_string_io_mmio(mem);
> >>
> >> +     test_bpl_modrm(mem, insn_page, alt_insn_page, insn_ram);
> >> +
> >>       printf("\nSUMMARY: %d tests, %d failures\n", tests, fails);
> >>       return fails ? 1 : 0;
> >>  }
> >> --
> >> 1.7.9.5
> >
> > --
> >                         Gleb.

--
			Gleb.