Re: [coreboot] Disassembly of coreboot binaries

[Chauhan, Himanshu]

Hi Aaron,

I figured out the crash. It wan't because wrong load of the ROM image
(thanks to the nifty post_code which I could trap on IO). I see that
the page fault I am getting is in following code:
(gdb) list *(((0xfff81e41 - 0xfff80000)-200)+0x2000000)
0x2001d79 is in imd_recover (src/lib/imd.c:139).
134
135     static void imdr_init(struct imdr *ir, void *upper_limit)
136     {
137             uintptr_t limit = (uintptr_t)upper_limit;
138             /* Upper limit is aligned down to 4KiB */
139             ir->limit = ALIGN_DOWN(limit, LIMIT_ALIGN);
140             ir->r = NULL;
141     }
142
143     static int imdr_create_empty(struct imdr *imdr, size_t root_size,

I see that this function is being called multiple times (I added some
more post_code and see them being trapped). I get a series of page
faults which I am able to honour all but last.

(__handle_vm_exception:543) Guest fault: 0x7f7fffc (rIP: 00000000FFF81E41)
(__handle_vm_exception:543) Guest fault: 0x7f7effc (rIP: 00000000FFF81E41)
(__handle_vm_exception:543) Guest fault: 0x7f7dffc (rIP: 00000000FFF81E41)
(__handle_vm_exception:543) Guest fault: 0x7f7cffc (rIP: 00000000FFF81E41)
(__handle_vm_exception:543) Guest fault: 0x7f7bffc (rIP: 00000000FFF81E41)
(__handle_vm_exception:543) Guest fault: 0x7f7affc (rIP: 00000000FFF81E41)
(__handle_vm_exception:543) Guest fault: 0x7f79ffc (rIP: 00000000FFF81E41)
(__handle_vm_exception:543) Guest fault: 0x7f78ffc (rIP: 00000000FFF81E41)
(__handle_vm_exception:543) Guest fault: 0x7f77ffc (rIP: 00000000FFF81E41)
(__handle_vm_exception:543) Guest fault: 0x7f76ffc (rIP: 00000000FFF81E41)
<snip>

handle_guest_realmode_page_fault: offset: 0x3ffc fault: 0x1003ffc reg: 0x1000000
handle_guest_realmode_page_fault: offset: 0x2ffc fault: 0x1002ffc reg: 0x1000000
handle_guest_realmode_page_fault: offset: 0x1ffc fault: 0x1001ffc reg: 0x1000000
handle_guest_realmode_page_fault: offset: 0xffc fault: 0x1000ffc reg: 0x1000000

(__handle_vm_exception:561) ERROR: No region mapped to guest physical: 0xfffffc

I want to understand why imd_recover gets called multiple times
starting from top of memory (128MB is what I have assigned to the
guest) to 16MB last (after which I can't honour). There is something
amiss in my understanding of core boot memory map.

Could you please help?

Regards
Himanshu

On Wed, Dec 14, 2016 at 9:27 PM, Chauhan, Himanshu
 wrote:
> Hi Aaron,
>
> Yes, I am mapping the memory where coreboot.rom is loaded to upper 4GiB. I
> create a fixed shadow page table entry for reset vector.
>
> Coreboot doesn't have a linked address of RIP that I shared. I think with
> the increase in size of coreboot (from the previous tag I was using) the
> load address (guest physical) has changed. I used to calculate the load
> address manually. I will check this and get back.
>
> Thanks.
>
> On Wed, Dec 14, 2016 at 8:17 PM, Aaron Durbin  wrote:
> > On Wed, Dec 14, 2016 at 3:11 AM, Chauhan, Himanshu
> >  wrote:
> > > Hi,
> > >
> > > I am working on a hypvervisor and am using coreboot + FILO as guest
> > > BIOS.
> > > While things were fine a while back, it has stopped working. I see that
> > > my
> > > hypervisor can't handle address 0xFFFFFC while coreboot's RIP is at
> > > 0xfff81e41.
> >
> > How are you loading up coreboot.rom in the VM? Are you just memory
> > mapping it at the top of 4GiB address space? If so, what does
> > 'cbfstool coreboot.rom print' show?
> > > The exact register dump of guest is as follow:
> > >
> > > [guest0/uart0] (__handle_vm_exception:558) ERROR: No region mapped to
> > > guest
> > > physical: 0xfffffc
> > >
> > > GUEST guest0/vcpu0 dump state:
> > >
> > > RAX: 0x9fe80 RBX: 0xfffff8 RCX: 0x1b RDX: 0x53a11439
> > > R08: 0x0 R09: 0x0 R10: 0x0 R11: 0x0
> > > R12: 0x0 R13: 0x0 R14: 0x0 R15: 0x0
> > > RSP: 0x9fe54 RBP: 0xa0000 RDI: 0xfff801e4 RSI: 0x9fe80
> > > RIP: 0xfff81e41
> > >
> > > CR0: 0xe0000011 CR2: 0x0 CR3: 0xa23000 CR4: 0x0
> > > CS    : Sel: 0x00000008 Limit: 0xffffffff Base: 0x00000000 (G:  1 DB:  1
> > > L:
> > > 0 AVL:  0 P:  1 DPL:  0 S:  1 Type: 11)
> > > DS    : Sel: 0x00000010 Limit: 0xffffffff Base: 0x00000000 (G:  1 DB:  1
> > > L:
> > > 0 AVL:  0 P:  1 DPL:  0 S:  1 Type:  3)
> > > ES    : Sel: 0x00000010 Limit: 0xffffffff Base: 0x00000000 (G:  1 DB:  1
> > > L:
> > > 0 AVL:  0 P:  1 DPL:  0 S:  1 Type:  3)
> > > SS    : Sel: 0x00000010 Limit: 0xffffffff Base: 0x00000000 (G:  1 DB:  1
> > > L:
> > > 0 AVL:  0 P:  1 DPL:  0 S:  1 Type:  3)
> > > FS    : Sel: 0x00000010 Limit: 0xffffffff Base: 0x00000000 (G:  1 DB:  1
> > > L:
> > > 0 AVL:  0 P:  1 DPL:  0 S:  1 Type:  3)
> > > GS    : Sel: 0x00000010 Limit: 0xffffffff Base: 0x00000000 (G:  1 DB:  1
> > > L:
> > > 0 AVL:  0 P:  1 DPL:  0 S:  1 Type:  3)
> > > GDT   : Sel: 0x00000000 Limit: 0x0000001f Base: 0xfff80200 (G:  0 DB:  0
> > > L:
> > > 0 AVL:  0 P:  0 DPL:  0 S:  0 Type:  0)
> > > LDT   : Sel: 0x00000000 Limit: 0x0000ffff Base: 0x00000000 (G:  0 DB:  0
> > > L:
> > > 0 AVL:  0 P:  0 DPL:  0 S:  0 Type:  0)
> > > IDT   : Sel: 0x00000000 Limit: 0x00000000 Base: 0x00000000 (G:  0 DB:  0
> > > L:
> > > 0 AVL:  0 P:  0 DPL:  0 S:  0 Type:  0)
> > > TR    : Sel: 0x00000000 Limit: 0x0000ffff Base: 0x00000000 (G:  1 DB:  0
> > > L:
> > > 1 AVL:  1 P:  0 DPL:  0 S:  0 Type:  0)
> > > RFLAGS: 0xa    [ ]
> > >
> > > I want to know which binary file (.o) should I disassemble to look at
> > > the
> > > RIP?
> > >
> > > I was looking at
> > > objdump -D  -mi386 -Maddr16,data16 generated/ramstage.o
> > >
> > > but this is prior to linking and thus only has offsets.
> > >
> > > Regards
> > > [Himanshu Chauhan]
>
> Regards
> [Himanshu Chauhan]