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Wed, 22 Jul 2026 21:55:14 +0000 Message-ID: <327a68cc-c15f-45fa-ba71-e9e89fc0207e@intel.com> Date: Wed, 22 Jul 2026 14:55:13 -0700 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 13/20] KVM: x86: Reject EVEX-prefixed instructions To: CC: References: <20260720171949.498680-1-chang.seok.bae@intel.com> <20260720171949.498680-14-chang.seok.bae@intel.com> <20260720181110.C975E1F000E9@smtp.kernel.org> Content-Language: en-US From: "Chang S. 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> > [Severity: Low] > Does this evaluate stale data in ctxt->modrm? > > When a 32-bit guest executes an instruction starting with 0x62 in > x86_decode_insn(), opcode_table[0x62] yields NotImpl, which lacks the ModRM > flag. Because the ModRM flag is missing, insn_fetch() is bypassed. > > Since the EVEX check doesn't short-circuit in 32-bit mode, it will evaluate > whatever stale data remains in ctxt->modrm from a prior emulation on that > context. > > Because opcode.flags is already initialized to NotImpl by the table lookup, > is this check entirely redundant? Even if it is not be the most optimized form, I still think it keeps the logic straightforward. Thank, Chang