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
>>
>>
>
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