x86emul: fix {,i}mul and {,i}div Commit a3db233ede ("x86emul: use DstEax also for {,I}{MUL,DIV}") went a little too far: DstEax and SrcEax weren't really meant to be used together with ModRM - they assume modrm_reg remains zero by the time the destination / source register pointer gets calculated. Don't fully undo that commit though, but instead just correct the register pointer, and don't use dst.val as input for mul and imul (div and idiv did avoid that already). Reported-by: Konrad Rzeszutek Wilk Signed-off-by: Jan Beulich --- a/xen/arch/x86/x86_emulate/x86_emulate.c +++ b/xen/arch/x86/x86_emulate/x86_emulate.c @@ -3845,18 +3845,19 @@ x86_emulate( emulate_1op("neg", dst, _regs.eflags); break; case 4: /* mul */ + dst.reg = (unsigned long *)&_regs.eax; _regs.eflags &= ~(EFLG_OF|EFLG_CF); switch ( dst.bytes ) { case 1: - dst.val = (uint8_t)dst.val; + dst.val = (uint8_t)_regs.eax; dst.val *= src.val; if ( (uint8_t)dst.val != (uint16_t)dst.val ) _regs.eflags |= EFLG_OF|EFLG_CF; dst.bytes = 2; break; case 2: - dst.val = (uint16_t)dst.val; + dst.val = (uint16_t)_regs.eax; dst.val *= src.val; if ( (uint16_t)dst.val != (uint32_t)dst.val ) _regs.eflags |= EFLG_OF|EFLG_CF; @@ -3864,7 +3865,7 @@ x86_emulate( break; #ifdef __x86_64__ case 4: - dst.val = (uint32_t)dst.val; + dst.val = _regs._eax; dst.val *= src.val; if ( (uint32_t)dst.val != dst.val ) _regs.eflags |= EFLG_OF|EFLG_CF; @@ -3873,7 +3874,7 @@ x86_emulate( #endif default: u[0] = src.val; - u[1] = dst.val; + u[1] = _regs.eax; if ( mul_dbl(u) ) _regs.eflags |= EFLG_OF|EFLG_CF; _regs.edx = u[1]; @@ -3882,12 +3883,13 @@ x86_emulate( } break; case 5: /* imul */ + dst.reg = (unsigned long *)&_regs.eax; imul: _regs.eflags &= ~(EFLG_OF|EFLG_CF); switch ( dst.bytes ) { case 1: - dst.val = (int8_t)src.val * (int8_t)dst.val; + dst.val = (int8_t)src.val * (int8_t)_regs.eax; if ( (int8_t)dst.val != (int16_t)dst.val ) _regs.eflags |= EFLG_OF|EFLG_CF; ASSERT(b > 0x6b); @@ -3895,7 +3897,7 @@ x86_emulate( break; case 2: dst.val = ((uint32_t)(int16_t)src.val * - (uint32_t)(int16_t)dst.val); + (uint32_t)(int16_t)_regs.eax); if ( (int16_t)dst.val != (int32_t)dst.val ) _regs.eflags |= EFLG_OF|EFLG_CF; if ( b > 0x6b ) @@ -3904,7 +3906,7 @@ x86_emulate( #ifdef __x86_64__ case 4: dst.val = ((uint64_t)(int32_t)src.val * - (uint64_t)(int32_t)dst.val); + (uint64_t)(int32_t)_regs.eax); if ( (int32_t)dst.val != dst.val ) _regs.eflags |= EFLG_OF|EFLG_CF; if ( b > 0x6b ) @@ -3913,7 +3915,7 @@ x86_emulate( #endif default: u[0] = src.val; - u[1] = dst.val; + u[1] = _regs.eax; if ( imul_dbl(u) ) _regs.eflags |= EFLG_OF|EFLG_CF; if ( b > 0x6b ) @@ -3923,6 +3925,7 @@ x86_emulate( } break; case 6: /* div */ + dst.reg = (unsigned long *)&_regs.eax; switch ( src.bytes ) { case 1: @@ -3968,6 +3971,7 @@ x86_emulate( } break; case 7: /* idiv */ + dst.reg = (unsigned long *)&_regs.eax; switch ( src.bytes ) { case 1: