Messages in this thread | | | Subject | Re: [PATCH 0/4] x86/module: Out-of-tree module decode and sanitize | From | Andrew Cooper <> | Date | Tue, 7 Apr 2020 21:21:31 +0100 |
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On 07/04/2020 20:41, Peter Zijlstra wrote: > On Tue, Apr 07, 2020 at 06:23:27PM +0100, Andrew Cooper wrote: >> On 07/04/2020 12:02, Peter Zijlstra wrote: >>> Hi all, >>> >>> Driven by the SLD vs VMX interaction, here are some patches that provide means >>> to analyze the text of out-of-tree modules. >>> >>> The first user of that is refusing to load modules on VMX-SLD conflicts, but it >>> also has a second patch that refulses to load any module that tries to modify >>> CRn/DRn. >>> >>> I'm thinking people will quickly come up with more and more elaborate tests to >>> which to subject out-of-tree modules. >> Anything playing with LGDT & friends? Shouldn't be substantially more >> elaborate than CR/DR to check for. > More friends? (I wasn't sure on the Sxxx instructions, they appear > harmless, but what do I know..) > > I was also eyeing LSL LTR LSS, none of which I figured a module has any > business of using. Are there more? > > --- a/arch/x86/kernel/module.c > +++ b/arch/x86/kernel/module.c > @@ -282,6 +282,50 @@ static bool insn_is_mov_DRn(struct insn > return false; > } > > +static bool insn_is_LxDT(struct insn *insn) > +{ > + u8 modrm = insn->modrm.bytes[0]; > + u8 modrm_mod = X86_MODRM_MOD(modrm); > + u8 modrm_reg = X86_MODRM_REG(modrm); > + > + if (insn->opcode.bytes[0] != 0x0f) > + return false; > + > + switch (insn->opcode.bytes[1]) { > + case 0x00: > + if (modrm_mod != 0x03) > + break; > +
Apologies - missed this before. LLDT and LTR can be encoded with a memory operand, so you need to drop the modrm_mod check to spot all instances.
~Andrew
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