Re: [tip: objtool/core] objtool/x86: objtool can confuse memory and stack access

[Alexandre Chartre]

On 7/8/24 18:48, Borislav Petkov wrote:
> On Mon, Jul 08, 2024 at 11:49:24AM -0000, tip-bot2 for Alexandre Chartre wrote:
> >   4c 8b 24 25 e0 ff ff    mov    0xffffffffffffffe0,%r12
>
> Right, this is missing a "ff" which is the 4th byte of a disp32.
>
> I.e., ModRM=0, SIB=5 simply means that what follows is a disp32 field:
>
>   REX:                   0x4c { 4 [w]: 1 [r]: 1 [x]: 0 [b]: 0 }
> Opcode:                 0x8b
> ModRM:                  0x24  [mod:0b][.R:1b,reg:1100b][.B:0b,r/m:100b]
>                          register-indirect mode, offset 0
> SIB:                    0x25 [.B:0b,base:101b][.X:0b,idx:100b][scale: 0]
>
>   MOV Gv,Ev; MOV reg{16,32,64} reg/mem{16,32,64}
>                 0:       4c 8b 24 25 e0 ff ff    mov 0xffffffffffffffe0,%r12
>                 7:       ff

Ah! Right. I regularly got tricked when the opcode is output on two lines :-(

Sorry.

alex.