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Message-ID: <YUycliX+lPSMhWfR@otcwcpicx3.sc.intel.com> Date: Thu, 23 Sep 2021 15:26:14 +0000 From: Fenghua Yu <fenghua.yu@...el.com> To: Peter Zijlstra <peterz@...radead.org> Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, Andy Lutomirski <luto@...nel.org>, Dave Hansen <dave.hansen@...el.com>, Tony Luck <tony.luck@...el.com>, Lu Baolu <baolu.lu@...ux.intel.com>, Joerg Roedel <joro@...tes.org>, Josh Poimboeuf <jpoimboe@...hat.com>, Dave Jiang <dave.jiang@...el.com>, Jacob Jun Pan <jacob.jun.pan@...el.com>, Ashok Raj <ashok.raj@...el.com>, Ravi V Shankar <ravi.v.shankar@...el.com>, iommu@...ts.linux-foundation.org, x86 <x86@...nel.org>, linux-kernel <linux-kernel@...r.kernel.org> Subject: Re: [PATCH 7/8] tools/objtool: Check for use of the ENQCMD instruction in the kernel Hi, Peter, On Thu, Sep 23, 2021 at 09:17:01AM +0200, Peter Zijlstra wrote: > On Wed, Sep 22, 2021 at 11:44:41PM +0000, Fenghua Yu wrote: > > > > Since you're making it a fatal error, before doing much of anything > > > else, you might at well fail decode and keep it all in the x86/decode.c > > > file, no need to spread this 'knowledge' any further. > > > Is the following updated patch a right one? > > Yes, that's what I was thinking of. > > > diff --git a/tools/objtool/arch/x86/decode.c b/tools/objtool/arch/x86/decode.c > > index bc821056aba9..3e0f928e28a5 100644 > > --- a/tools/objtool/arch/x86/decode.c > > +++ b/tools/objtool/arch/x86/decode.c > > @@ -110,7 +110,7 @@ int arch_decode_instruction(const struct elf *elf, const struct section *sec, > > { > > struct insn insn; > > int x86_64, ret; > > - unsigned char op1, op2, > > + unsigned char op1, op2, op3, > > rex = 0, rex_b = 0, rex_r = 0, rex_w = 0, rex_x = 0, > > modrm = 0, modrm_mod = 0, modrm_rm = 0, modrm_reg = 0, > > sib = 0, /* sib_scale = 0, */ sib_index = 0, sib_base = 0; > > @@ -137,6 +137,7 @@ int arch_decode_instruction(const struct elf *elf, const struct section *sec, > > > > op1 = insn.opcode.bytes[0]; > > op2 = insn.opcode.bytes[1]; > > + op3 = insn.opcode.bytes[2]; > > > > if (insn.rex_prefix.nbytes) { > > rex = insn.rex_prefix.bytes[0]; > > @@ -489,6 +490,16 @@ int arch_decode_instruction(const struct elf *elf, const struct section *sec, > > /* nopl/nopw */ > > *type = INSN_NOP; > > > > + } else if (op2 == 0x38 && op3 == 0xf8) { > > + if (insn.prefixes.nbytes == 1 && > > + insn.prefixes.bytes[0] == 0xf2) { > > + /* ENQCMD cannot be used in the kernel. */ > > + WARN("ENQCMD instruction at %s:%lx", sec->name, > > + offset); > > + > > + return -1; > > + } > > The only concern here is if we want it to be fatal or not. But otherwise > this seems to be all that's required. objtool doesn't fail kernel build on this fatal warning. Returning -1 here stops checking the rest of the file and won't report any further warnings unless this ENQCMD warning is fixed. Not returning -1 continues checking the rest of the file and may report more warnings. Seems that's the only difference b/w them. Should I keep this "return -1" or not? Please advice. -Fenghua
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