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Wed, 2 Jul 2025 00:36:09 +0000 Message-ID: <63a44def-fd5d-4f21-8d09-bb608cfab524@intel.com> Date: Tue, 1 Jul 2025 17:36:06 -0700 User-Agent: Mozilla Thunderbird Subject: Re: [PATCHv8 12/17] x86/traps: Communicate a LASS violation in #GP message Content-Language: en-US To: "Kirill A. Shutemov" , Andy Lutomirski , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , , "H. Peter Anvin" , Peter Zijlstra , Ard Biesheuvel , "Paul E. 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Shutemov wrote: > /* > @@ -672,6 +681,12 @@ static enum kernel_gp_hint get_kernel_gp_address(struct pt_regs *regs, > if (*addr < ~__VIRTUAL_MASK && > *addr + insn.opnd_bytes - 1 > __VIRTUAL_MASK) > return GP_NON_CANONICAL; > + else if (*addr < ~__VIRTUAL_MASK && > + cpu_feature_enabled(X86_FEATURE_LASS)) { > + if (*addr < PAGE_SIZE) > + return GP_NULL_POINTER; > + return GP_LASS_VIOLATION; > + } The comments above this section of code say: /* * Check that: * - the operand is not in the kernel half * - the last byte of the operand is not in the user canonical half */ They should be updated since we are updating the logic. Also, below is easier to read than above: if (*addr < ~__VIRTUAL_MASK) { if (*addr + insn.opnd_bytes - 1 > __VIRTUAL_MASK) return EXC_NON_CANONICAL; if (cpu_feature_enabled(X86_FEATURE_LASS)) { if (*addr < PAGE_SIZE) return EXC_NULL_POINTER; return EXC_LASS_VIOLATION; } } I am wondering if the NULL pointer exception should be made unconditional, even if it is unlikely to reach here without LASS. So maybe something like this: if (*addr < ~__VIRTUAL_MASK) { if (*addr + insn.opnd_bytes - 1 > __VIRTUAL_MASK) return EXC_NON_CANONICAL; if (*addr < PAGE_SIZE) return EXC_NULL_POINTER; if (cpu_feature_enabled(X86_FEATURE_LASS)) return EXC_LASS_VIOLATION; }