Hi Keir,
I think the 7th issue I mentioned is the root cause,
so I have a question.
For real mode simulation, the simulator is running in the same space
with the codes to-be-simulated? then how to protect simulator from
being modified by to-be-simulated code?
can I change the address of vmxassist to a higher address? just try to
give more space to the to-be-simulated windows.
On 8/8/07, Brady Chen <chenchp@xxxxxxxxx> wrote:
> it's possible.
> any ideas to trace the function stack of xen guest? like "bt" command in gdb.
>
> I did some analysis:
> 1. the call flow is opcode()->fetch8()->address()
> 2. only the printf in address() will change the behaver of crash.
> 3. and the crash EIP (0xD0800) is in the address() from the objdump.
> 4. the address() will be invoked more then 40, 000 times in one
> simulation, before the crash.
> 5. seems there are no recursive invoking in opcode(), fetch8(), address()
> 6. from the output of "xen dmesg", before the crash, a instructions
> sequence is simulated several times (you could check the previous
> mails i send for "xen dmesg" output)
> 7. before the trap, the simulated instruction is "movw %ax, *0xD07FE",
> and the "*0xD07FE" is just the address of address(), (you could get
> the objdump output from previous mails too), so i think it's the
> simulation which crash the memory of address().
>
> On 8/8/07, Keir Fraser <keir@xxxxxxxxxxxxx> wrote:
> > Stack corruption/overflow, possibly?
> >
> > K.
> >
> > On 7/8/07 17:06, "Brady Chen" <chenchp@xxxxxxxxx> wrote:
> >
> > > Yes, the printfs are the only changes. once I remove these prints, the
> > > trap comes back, with the same EIP (D0800)
> > >
> > > I tried to keep the first two printfs, the trap comes with different
> > > EIP(D19FD)
> > > static unsigned
> > > address(struct regs *regs, unsigned seg, unsigned off)
> > > {
> > > uint64_t gdt_phys_base;
> > > unsigned long long entry;
> > > unsigned seg_base, seg_limit;
> > > unsigned entry_low, entry_high;
> > >
> > > printf("f 1\n");
> > > if (seg == 0) {
> > > if (mode == VM86_REAL || mode == VM86_REAL_TO_PROTECTED)
> > > return off;
> > > else
> > > panic("segment is zero, but not in real mode!\n");
> > > }
> > >
> > > printf("f 2\n");
> > >
> > > xen dmesg output:
> > > (XEN) HVM3: 0x0000D71F: 0xD00:0x071F (0) opc 0x83
> > > (XEN) HVM3: f 1
> > > (XEN) HVM3: f 2
> > > (XEN) HVM3: 0x0000D71F: 0xD00:0x071F (0) external interrupt 8
> > > (XEN) HVM3: f 1
> > > (XEN) HVM3: f 1
> > > (XEN) HVM3: f 1
> > > (XEN) HVM3: Trap (0x6) while in real mode
> > > (XEN) HVM3: eax CFAE ecx 0 edx 0 ebx
> > > D75B4
> > > (XEN) HVM3: esp D7564 ebp D75A0 esi 71F edi
> > > 8
> > > (XEN) HVM3: trapno 6 errno 0
> > > (XEN) HVM3: eip D19FD cs 10 eflags 13046
> > > (XEN) HVM3: uesp CFAE uss 0
> > > (XEN) HVM3: ves D4C44 vds 8 vfs 83 vgs
> > > 71F
> > > (XEN) HVM3: cr0 50032 cr2 0 cr3 0 cr4
> > > 651
> > > (XEN) HVM3:
> > > (XEN) HVM3: Halt called from %eip 0xD037C
> > >
> > >
> > > and the objdump shows that:
> > > 000d1970 <interrupt>:
> > > d1970: 55 push %ebp
> > > d1971: 89 e5 mov %esp,%ebp
> > > d1973: 57 push %edi
> > > d1974: 89 d7 mov %edx,%edi
> > > d1976: 56 push %esi
> > > ....
> > > d19f8: 66 89 30 mov %si,(%eax)
> > > d19fb: 31 d2 xor %edx,%edx
> > > d19fd: 8d 34 bd 00 00 00 00 lea 0x0(,%edi,4),%esi
> > > d1a04: 81 63 30 ff fd ff ff andl $0xfffffdff,0x30(%ebx)
> > > d1a0b: 89 d8 mov %ebx,%eax
> > > d1a0d: 89 34 24 mov %esi,(%esp)
> > >
> > >
> > > On 8/7/07, Keir Fraser <keir@xxxxxxxxxxxxx> wrote:
> > >> Very weird. The emulations now aren't at the same address as before
> > >> either
> > >> (0xd4c3 rather than 0xd71b). Is the *only* difference that you added
> > >> these
> > >> printf()s -- is it at all possible that the guest is executing down a
> > >> different path here for other reasons? If it's really down to the
> > >> printf()s
> > >> then I guess you'll have to shuffle/remove printf()s to get the old
> > >> behaviour back.
> > >>
> > >> -- Keir
> > >>
> > >> On 7/8/07 12:35, "Brady Chen" <chenchp@xxxxxxxxx> wrote:
> > >>
> > >>> it's strange:
> > >>> if i add these prints, i get " Unknown opcode", not "trap".
> > >>> ===added printf
> > >>> [root@localhost firmware]# hg diff -p vmxassist/vm86.c
> > >>> diff -r 6f18f5bdeea3 tools/firmware/vmxassist/vm86.c
> > >>> --- a/tools/firmware/vmxassist/vm86.c Mon Aug 06 15:33:42 2007 +0100
> > >>> +++ b/tools/firmware/vmxassist/vm86.c Tue Aug 07 19:33:55 2007 +0800
> > >>> @@ -40,7 +40,7 @@ static struct regs saved_rm_regs;
> > >>> static struct regs saved_rm_regs;
> > >>>
> > >>> #ifdef DEBUG
> > >>> -int traceset = 0;
> > >>> +int traceset = ~0;
> > >>>
> > >>> char *states[] = {
> > >>> "<VM86_REAL>",
> > >>> @@ -128,6 +128,7 @@ address(struct regs *regs, unsigned seg,
> > >>> unsigned seg_base, seg_limit;
> > >>> unsigned entry_low, entry_high;
> > >>>
> > >>> + printf("f 1\n");
> > >>> if (seg == 0) {
> > >>> if (mode == VM86_REAL || mode == VM86_REAL_TO_PROTECTED)
> > >>> return off;
> > >>> @@ -135,12 +136,16 @@ address(struct regs *regs, unsigned seg,
> > >>> panic("segment is zero, but not in real
> > >>> mode!\n");
> > >>> }
> > >>>
> > >>> + printf("f 2\n");
> > >>> if (mode == VM86_REAL || seg > oldctx.gdtr_limit ||
> > >>> (mode == VM86_REAL_TO_PROTECTED && regs->cs == seg))
> > >>> return ((seg & 0xFFFF) << 4) + off;
> > >>>
> > >>> + printf("f 3\n");
> > >>> gdt_phys_base = guest_linear_to_phys(oldctx.gdtr_base);
> > >>> + printf("f 4\n");
> > >>> if (gdt_phys_base != (uint32_t)gdt_phys_base) {
> > >>> + printf("f 5\n");
> > >>> printf("gdt base address above 4G\n");
> > >>> cpuid_addr_value(gdt_phys_base + 8 * (seg >> 3),
> > >>> &entry);
> > >>> } else
> > >>> @@ -152,14 +157,17 @@ address(struct regs *regs, unsigned seg,
> > >>> seg_base = (entry_high & 0xFF000000) | ((entry >> 16) &
> > >>> 0xFFFFFF);
> > >>> seg_limit = (entry_high & 0xF0000) | (entry_low & 0xFFFF);
> > >>>
> > >>> + printf("f 6\n");
> > >>> if (entry_high & 0x8000 &&
> > >>> ((entry_high & 0x800000 && off >> 12 <= seg_limit) ||
> > >>> (!(entry_high & 0x800000) && off <= seg_limit)))
> > >>> return seg_base + off;
> > >>> + printf("f 7\n");
> > >>>
> > >>> panic("should never reach here in function address():\n\t"
> > >>> "entry=0x%08x%08x, mode=%d, seg=0x%08x,
> > >>> offset=0x%08x\n",
> > >>> entry_high, entry_low, mode, seg, off);
> > >>> + printf("f 8\n");
> > >>>
> > >>> return 0;
> > >>> }
> > >>> @@ -286,6 +294,7 @@ fetch8(struct regs *regs)
> > >>> unsigned addr = address(regs, regs->cs, MASK16(regs->eip));
> > >>>
> > >>> regs->eip++;
> > >>> + printf("f 9\n");
> > >>> return read8(addr);
> > >>> }
> > >>>
> > >>> ===output when add many printf
> > >>> (XEN) HVM12: 0x0000D4C3: 0xD00:0x04C3 (0) addr32addr32f 1
> > >>> (XEN) HVM12: f 2
> > >>> (XEN) HVM12: f 9
> > >>> (XEN) HVM12: f 1
> > >>> (XEN) HVM12: f 2
> > >>> (XEN) HVM12: 0x0000D4C3: 0xD00:0x04C3 (0) data32data32f 1
> > >>> (XEN) HVM12: f 2
> > >>> (XEN) HVM12: f 9
> > >>> (XEN) HVM12: f 1
> > >>> (XEN) HVM12: f 2
> > >>> (XEN) HVM12: 0x0000D4C3: 0xD00:0x04C3 (0) opc 0x83opc 0xD7704f 1
> > >>> (XEN) HVM12: f 2
> > >>> (XEN) HVM12: Unknown opcode at 0D00:04C3=0xD4C3
> > >>> (XEN) HVM12: Halt called from %eip 0xD3B4A
> > >>>
> > >>> On 8/7/07, Brady Chen <chenchp@xxxxxxxxx> wrote:
> > >>>> Hi, yes, it's crashed in fetch8. it's very slow after I add this print
> > >>>> info.
> > >>>> the main function of fetch8 seems to be address(). seems crashed in
> > >>>> address().
> > >>>>
> > >>>> (XEN) HVM7: after write16 of movw
> > >>>> (XEN) HVM7: top of opcode
> > >>>> (XEN) HVM7: Before fetch8
> > >>>> (XEN) HVM7: eax 7E80 ecx 2D1B edx 0 ebx
> > >>>> 404E
> > >>>> (XEN) HVM7: esp D76F4 ebp 1FF0 esi 7BE edi
> > >>>> C37FE
> > >>>> (XEN) HVM7: trapno D errno 0
> > >>>> (XEN) HVM7: eip 71F cs D00 eflags 33206
> > >>>> (XEN) HVM7: uesp CFB4 uss 0
> > >>>> (XEN) HVM7: ves D00 vds D00 vfs 0 vgs
> > >>>> 0
> > >>>> (XEN) HVM7: cr0 50032 cr2 0 cr3 0 cr4
> > >>>> 651
> > >>>> (XEN) HVM7:
> > >>>> (XEN) HVM7: Trap (0x6) while in real mode
> > >>>> (XEN) HVM7: eax D00 ecx 0 edx 71F ebx
> > >>>> 89
> > >>>> (XEN) HVM7: esp D75E4 ebp D7630 esi D7620 edi
> > >>>> D00
> > >>>> (XEN) HVM7: trapno 6 errno 0
> > >>>> (XEN) HVM7: eip D0800 cs 10 eflags 13046
> > >>>> (XEN) HVM7: uesp 71F uss D76D4
> > >>>> (XEN) HVM7: ves D7610 vds D3AB9 vfs D762C vgs
> > >>>> D7644
> > >>>> (XEN) HVM7: cr0 50032 cr2 0 cr3 0 cr4
> > >>>> 651
> > >>>> (XEN) HVM7:
> > >>>> (XEN) HVM7: 0xd0800 is 0xFFFF
> > >>>> (XEN) HVM7: 0xd0804 is 0x7D8B
> > >>>> (XEN) HVM7: Halt called from %eip 0xD037C
> > >>>>
> > >>>>
> > >>>> On 8/7/07, Keir Fraser <keir@xxxxxxxxxxxxx> wrote:
> > >>>>> How about trying:
> > >>>>> printf("Before fetch8\n");
> > >>>>> dump_regs(regs);
> > >>>>> opc = fetch8(regs);
> > >>>>> printf("After fetch8\n");
> > >>>>> switch (opc) { ...
> > >>>>>
> > >>>>> This will let you see what eip is being fetched from, and also confirm
> > >>>>> that
> > >>>>> the crash happens within fetch8().
> > >>>>>
> > >>>>> You could also try adding more printf()s inside fetch8() and
> > >>>>> address() to
> > >>>>> find out which specific bit of fetch8() is crashing (if that indeed
> > >>>>> the
> > >>>>> function that is crashing).
> > >>>>>
> > >>>>> -- Keir
> > >>>>>
> > >>>>> On 7/8/07 11:30, "Brady Chen" <chenchp@xxxxxxxxx> wrote:
> > >>>>>
> > >>>>>> Hi, Keir,
> > >>>>>> I made the change as you said:
> > >>>>>> change diff is:
> > >>>>>> [root@localhost firmware]# hg diff vmxassist/vm86.c
> > >>>>>> diff -r 6f18f5bdeea3 tools/firmware/vmxassist/vm86.c
> > >>>>>> --- a/tools/firmware/vmxassist/vm86.c Mon Aug 06 15:33:42 2007
> > >>>>>> +0100
> > >>>>>> +++ b/tools/firmware/vmxassist/vm86.c Tue Aug 07 18:26:12 2007
> > >>>>>> +0800
> > >>>>>> @@ -40,7 +40,7 @@ static struct regs saved_rm_regs;
> > >>>>>> static struct regs saved_rm_regs;
> > >>>>>>
> > >>>>>> #ifdef DEBUG
> > >>>>>> -int traceset = 0;
> > >>>>>> +int traceset = ~0;
> > >>>>>>
> > >>>>>> char *states[] = {
> > >>>>>> "<VM86_REAL>",
> > >>>>>> @@ -620,6 +620,7 @@ movr(struct regs *regs, unsigned prefix,
> > >>>>>> TRACE((regs, regs->eip - eip,
> > >>>>>> "movw %%%s, *0x%x", rnames[r],
> > >>>>>> addr));
> > >>>>>> write16(addr, MASK16(val));
> > >>>>>> + printf("after write16 of movw\n");
> > >>>>>> }
> > >>>>>> return 1;
> > >>>>>>
> > >>>>>> @@ -1305,6 +1306,7 @@ opcode(struct regs *regs)
> > >>>>>> unsigned eip = regs->eip;
> > >>>>>> unsigned opc, modrm, disp;
> > >>>>>> unsigned prefix = 0;
> > >>>>>> + printf("top of opcode\n");
> > >>>>>>
> > >>>>>> if (mode == VM86_PROTECTED_TO_REAL &&
> > >>>>>> oldctx.cs_arbytes.fields.default_ops_size) {
> > >>>>>> @@ -1712,6 +1714,8 @@ trap(int trapno, int errno, struct regs
> > >>>>>> if (trapno == 14)
> > >>>>>> printf("Page fault address 0x%x\n",
> > >>>>>> get_cr2());
> > >>>>>> dump_regs(regs);
> > >>>>>> + printf("0xd0800 is 0x%0x\n", *((unsigned
> > >>>>>> short*)0xd0800));
> > >>>>>> + printf("0xd0804 is 0x%0x\n", *((unsigned
> > >>>>>> short*)0xd0804));
> > >>>>>> halt();
> > >>>>>> }
> > >>>>>> }
> > >>>>>>
> > >>>>>>
> > >>>>>> here is the output:
> > >>>>>> (XEN) HVM6: top of opcode
> > >>>>>> (XEN) HVM6: 0x0000D71F: 0xD00:0x071F (0) data32
> > >>>>>> (XEN) HVM6: 0x0000D71F: 0xD00:0x071F (0) opc 0x83
> > >>>>>> (XEN) HVM6: top of opcode
> > >>>>>> (XEN) HVM6: 0x0000D71B: 0xD00:0x071B (0) %es:
> > >>>>>> (XEN) HVM6: 0x0000D71B: 0xD00:0x071B (0) addr32
> > >>>>>> (XEN) HVM6: 0x0000D71D: 0xD00:0x071D (0) movw %ax, *0xD07FE
> > >>>>>> (XEN) HVM6: after write16 of movw
> > >>>>>> (XEN) HVM6: top of opcode
> > >>>>>> (XEN) HVM6: Trap (0x6) while in real mode
> > >>>>>> (XEN) HVM6: eax D00 ecx 0 edx 71F ebx
> > >>>>>> 71E
> > >>>>>> (XEN) HVM6: esp D7554 ebp D75A0 esi D7590 edi
> > >>>>>> D00
> > >>>>>> (XEN) HVM6: trapno 6 errno 0
> > >>>>>> (XEN) HVM6: eip D0800 cs 10 eflags 13046
> > >>>>>> (XEN) HVM6: uesp D4C29 uss 2
> > >>>>>> (XEN) HVM6: ves D4C18 vds D4D9C vfs D07FE vgs
> > >>>>>> D75B4
> > >>>>>> (XEN) HVM6: cr0 50032 cr2 0 cr3 0 cr4
> > >>>>>> 651
> > >>>>>> (XEN) HVM6:
> > >>>>>> (XEN) HVM6: 0xd0800 is 0xFFFF
> > >>>>>> (XEN) HVM6: 0xd0804 is 0x7D8B
> > >>>>>> (XEN) HVM6: Halt called from %eip 0xD037C
> > >>>>>>
> > >>>>>> objdump:
> > >>>>>> d07ef: e9 2f ff ff ff jmp d0723 <address+0x23>
> > >>>>>> d07f4: 8b 55 08 mov 0x8(%ebp),%edx
> > >>>>>> d07f7: 89 f8 mov %edi,%eax
> > >>>>>> d07f9: 8b 5d f4 mov 0xfffffff4(%ebp),%ebx
> > >>>>>> d07fc: 8b 75 f8 mov 0xfffffff8(%ebp),%esi
> > >>>>>> d07ff: 25 ff ff 00 00 and $0xffff,%eax
> > >>>>>> d0804: 8b 7d fc mov 0xfffffffc(%ebp),%edi
> > >>>>>> d0807: 89 ec mov %ebp,%esp
> > >>>>>> d0809: c1 e0 04 shl $0x4,%eax
> > >>>>>> d080c: 01 d0 add %edx,%eax
> > >>>>>> d080e: 5d pop %ebp
> > >>>>>>
> > >>>>>> seems the memory is correct, it's crashed in opcode()
> > >>>>>> and i think it's fetch8(regs) which crash the system. I tried
> > >>>>>> fetch8(regs) in trap(), but it cause more traps, and let the hvm
> > >>>>>> guest
> > >>>>>> be reset.
> > >>>>>>
> > >>>>>> On 8/7/07, Keir Fraser <keir@xxxxxxxxxxxxx> wrote:
> > >>>>>>> On 7/8/07 10:29, "Keir Fraser" <keir@xxxxxxxxxxxxx> wrote:
> > >>>>>>>
> > >>>>>>>> What would be useful is to try to add tracing to see how far
> > >>>>>>>> vmxassist
> > >>>>>>>> gets
> > >>>>>>>> after its last line of tracing before the trap occurs. That last
> > >>>>>>>> line
> > >>>>>>>> is
> > >>>>>>>> currently from vm86.c, line 620. You might try adding extra
> > >>>>>>>> printf()
> > >>>>>>>> statements imemdiately after the write16() on line 622, and also
> > >>>>>>>> at the
> > >>>>>>>> top
> > >>>>>>>> of the opcode() function. We need to find out at what point
> > >>>>>>>> vmxassist
> > >>>>>>>> is
> > >>>>>>>> jumping to this bogus address d0800.
> > >>>>>>>
> > >>>>>>> Oh, another possibility is that vmxassist has been corrupted in
> > >>>>>>> memory.
> > >>>>>>> This
> > >>>>>>> is particularly likely because, according to the objdump, the
> > >>>>>>> 'instruction'
> > >>>>>>> that starts at d0800 is actually valid (it'd be an ADD of some
> > >>>>>>> sort).
> > >>>>>>>
> > >>>>>>> So, within trap() you might want to read say 16 bytes starting at
> > >>>>>>> 0xd0800
> > >>>>>>> and printf() them. So we can see if they match what objdump says
> > >>>>>>> should
> > >>>>>>> be
> > >>>>>>> there.
> > >>>>>>>
> > >>>>>>> -- Keir
> > >>>>>>>
> > >>>>>>>
> > >>>>>>
> > >>>>>> _______________________________________________
> > >>>>>> Xen-devel mailing list
> > >>>>>> Xen-devel@xxxxxxxxxxxxxxxxxxx
> > >>>>>> http://lists.xensource.com/xen-devel
> > >>>>>
> > >>>>>
> > >>>>
> > >>>
> > >>> _______________________________________________
> > >>> Xen-devel mailing list
> > >>> Xen-devel@xxxxxxxxxxxxxxxxxxx
> > >>> http://lists.xensource.com/xen-devel
> > >>
> > >>
> > >
> > > _______________________________________________
> > > Xen-devel mailing list
> > > Xen-devel@xxxxxxxxxxxxxxxxxxx
> > > http://lists.xensource.com/xen-devel
> >
> >
>
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