From: Alexandre Chartre <alexandre.chartre@oracle.com>
To: Borislav Petkov <bp@alien8.de>, linux-kernel@vger.kernel.org
Cc: alexandre.chartre@oracle.com, linux-tip-commits@vger.kernel.org,
kernel test robot <lkp@intel.com>,
Josh Poimboeuf <jpoimboe@kernel.org>,
x86@kernel.org
Subject: Re: [tip: objtool/core] objtool/x86: objtool can confuse memory and stack access
Date: Tue, 9 Jul 2024 10:00:21 +0200 [thread overview]
Message-ID: <5a2fb3b0-e469-43b4-b914-4ca0ad16b808@oracle.com> (raw)
In-Reply-To: <20240708164846.GFZowYbmQpBu2Y4GeL@fat_crate.local>
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.
prev parent reply other threads:[~2024-07-09 8:00 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-06-20 14:47 [PATCH V2 RESEND] " Alexandre Chartre
2024-07-03 6:43 ` Josh Poimboeuf
2024-07-08 11:49 ` [tip: objtool/core] " tip-bot2 for Alexandre Chartre
2024-07-08 16:48 ` Borislav Petkov
2024-07-09 8:00 ` Alexandre Chartre [this message]
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