From 673806d02e76629b4a6d0b145adc76af5b660aae Mon Sep 17 00:00:00 2001 From: Alejandro Vallejo Date: Thu, 27 Aug 2026 08:05:53 +0200 Subject: [PATCH] x86/hvm: Un-indent the HVM_FEP block in the #UD handler FEP is now the only reason for the #UD handler to run. While the #UD handler is unreachable when CONFIG_HVM_FEP is disabled, it's helpful to keep the function around. Reinject #UD in the non-FEP case so DCE can remove the rest. Signed-off-by: Alejandro Vallejo Reviewed-by: Jan Beulich --- xen/arch/x86/hvm/hvm.c | 59 +++++++++++++++++++++--------------------- 1 file changed, 29 insertions(+), 30 deletions(-) diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c index 955fc062a5..9a4147b62e 100644 --- a/xen/arch/x86/hvm/hvm.c +++ b/xen/arch/x86/hvm/hvm.c @@ -3833,49 +3833,48 @@ int hvm_descriptor_access_intercept(uint64_t exit_info, void hvm_ud_intercept(struct cpu_user_regs *regs) { struct vcpu *cur = current; - bool should_emulate = false; struct hvm_emulate_ctxt ctxt; + const struct segment_register *cs; + uint32_t walk; + unsigned long addr; + char sig[5]; /* ud2; .ascii "xen" */ + + if ( !opt_hvm_fep ) + { + ASSERT_UNREACHABLE(); + goto reinject; + } hvm_emulate_init_once(&ctxt, NULL, regs); - if ( opt_hvm_fep ) + cs = &ctxt.seg_reg[x86_seg_cs]; + walk = ((ctxt.seg_reg[x86_seg_ss].dpl == 3) + ? PFEC_user_mode : 0) | PFEC_insn_fetch; + + if ( hvm_virtual_to_linear_addr(x86_seg_cs, cs, regs->rip, + sizeof(sig), hvm_access_insn_fetch, + cs, &addr) && + (hvm_copy_from_guest_linear(sig, addr, sizeof(sig), + walk, NULL) == HVMTRANS_okay) && + (memcmp(sig, "\xf\xb" "xen", sizeof(sig)) == 0) ) { - const struct segment_register *cs = &ctxt.seg_reg[x86_seg_cs]; - uint32_t walk = ((ctxt.seg_reg[x86_seg_ss].dpl == 3) - ? PFEC_user_mode : 0) | PFEC_insn_fetch; - unsigned long addr; - char sig[5]; /* ud2; .ascii "xen" */ + regs->rip += sizeof(sig); + regs->eflags &= ~X86_EFLAGS_RF; - if ( hvm_virtual_to_linear_addr(x86_seg_cs, cs, regs->rip, - sizeof(sig), hvm_access_insn_fetch, - cs, &addr) && - (hvm_copy_from_guest_linear(sig, addr, sizeof(sig), - walk, NULL) == HVMTRANS_okay) && - (memcmp(sig, "\xf\xb" "xen", sizeof(sig)) == 0) ) - { - regs->rip += sizeof(sig); - regs->eflags &= ~X86_EFLAGS_RF; + /* Zero the upper 32 bits of %rip if not in 64bit mode. */ + if ( !(hvm_long_mode_active(cur) && cs->l) ) + regs->rip = (uint32_t)regs->rip; - /* Zero the upper 32 bits of %rip if not in 64bit mode. */ - if ( !(hvm_long_mode_active(cur) && cs->l) ) - regs->rip = (uint32_t)regs->rip; - - add_taint(TAINT_HVM_FEP); - - should_emulate = true; - } - } - - if ( !should_emulate ) - { - hvm_inject_hw_exception(X86_EXC_UD, X86_EVENT_NO_EC); - return; + add_taint(TAINT_HVM_FEP); } + else + goto reinject; switch ( hvm_emulate_one(&ctxt, VIO_no_completion) ) { case X86EMUL_UNHANDLEABLE: case X86EMUL_UNIMPLEMENTED: + reinject: hvm_inject_hw_exception(X86_EXC_UD, X86_EVENT_NO_EC); break; case X86EMUL_EXCEPTION: