From 7b6e05c50fc39466fcc685fb6d4216f99af58743 Mon Sep 17 00:00:00 2001 From: Andrew Cooper Date: Mon, 3 Dec 2018 18:11:40 +0000 Subject: [PATCH] x86/emul: Make POPF emulation easier to follow Signed-off-by: Andrew Cooper Reviewed-by: Jan Beulich --- xen/arch/x86/x86_emulate/x86_emulate.c | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-) diff --git a/xen/arch/x86/x86_emulate/x86_emulate.c b/xen/arch/x86/x86_emulate/x86_emulate.c index 03540b648f..717e02fe67 100644 --- a/xen/arch/x86/x86_emulate/x86_emulate.c +++ b/xen/arch/x86/x86_emulate/x86_emulate.c @@ -4198,6 +4198,10 @@ x86_emulate( goto push; case 0x9d: /* popf */ { + /* + * Bits which may not be modified by this instruction. RF is handled + * uniformly during instruction retirement. + */ uint32_t mask = X86_EFLAGS_VIP | X86_EFLAGS_VIF | X86_EFLAGS_VM; cr4 = 0; @@ -4211,15 +4215,20 @@ x86_emulate( if ( rc != X86EMUL_OKAY ) goto done; } + /* All IOPL != 3 POPFs fail, except in vm86 mode. */ generate_exception_if(!(cr4 & X86_CR4_VME) && MASK_EXTR(_regs.eflags, X86_EFLAGS_IOPL) != 3, EXC_GP, 0); } + /* + * IOPL cannot be modified outside of CPL 0. IF cannot be + * modified if IOPL < CPL. + */ mask |= X86_EFLAGS_IOPL; if ( !mode_iopl() ) mask |= X86_EFLAGS_IF; } - /* 64-bit mode: POP defaults to a 64-bit operand. */ + /* 64-bit mode: POPF defaults to a 64-bit operand. */ if ( mode_64bit() && (op_bytes == 4) ) op_bytes = 8; if ( (rc = read_ulong(x86_seg_ss, sp_post_inc(op_bytes), @@ -4227,7 +4236,9 @@ x86_emulate( goto done; if ( op_bytes == 2 ) { + /* 16-bit POPF preserves the upper 16 bits of EFLAGS. */ dst.val = (uint16_t)dst.val | (_regs.eflags & 0xffff0000u); + /* VME processing only applies at IOPL != 3. */ if ( (cr4 & X86_CR4_VME) && MASK_EXTR(_regs.eflags, X86_EFLAGS_IOPL) != 3 ) { -- 2.39.5