Nadav Amit <namit@xxxxxxxxxxxxxxxxx> writes:
> 32-bit operations are zero extended in 64-bit mode. Currently, the code does
> not handle them correctly and keeps the high bits. In 16-bit mode, the high
> 32-bits are kept intact.
>
> In addition, although it is not well-documented, when address override prefix
It would be helpful to have a pointer in the SDM especially for cases
that are not well-documented.
> is used with REP-string instruction, RCX high half is zeroed even if ECX was
> zero on the first iteration (as if an assignment was performed to ECX).
>
> Signed-off-by: Nadav Amit <namit@xxxxxxxxxxxxxxxxx>
> ---
> arch/x86/kvm/emulate.c | 38 +++++++++++++++++++++++---------------
> 1 file changed, 23 insertions(+), 15 deletions(-)
>
> diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
> index 743e8e3..6833b41 100644
> --- a/arch/x86/kvm/emulate.c
> +++ b/arch/x86/kvm/emulate.c
> @@ -434,9 +434,21 @@ static int emulator_check_intercept(struct x86_emulate_ctxt *ctxt,
> return ctxt->ops->intercept(ctxt, &info, stage);
> }
>
> -static void assign_masked(ulong *dest, ulong src, ulong mask)
> +static void assign_masked(ulong *dest, ulong src, int bytes)
> {
> - *dest = (*dest & ~mask) | (src & mask);
> + switch (bytes) {
> + case 2:
> + *dest = (u16)src | (*dest & ~0xfffful);
> + break;
> + case 4:
> + *dest = (u32)src;
> + break;
> + case 8:
> + *dest = src;
> + break;
> + default:
> + BUG();
IIRC, Paolo mentioned that a WARN() is preferable. But I see
a lot other places where BUG() is called, maybe, he can confirm.
> + }
> }
>
> static inline unsigned long ad_mask(struct x86_emulate_ctxt *ctxt)
> @@ -476,26 +488,20 @@ register_address(struct x86_emulate_ctxt *ctxt, unsigned long reg)
> return address_mask(ctxt, reg);
> }
>
> -static void masked_increment(ulong *reg, ulong mask, int inc)
> +static void masked_increment(ulong *reg, int size, int inc)
> {
> - assign_masked(reg, *reg + inc, mask);
> + assign_masked(reg, *reg + inc, size);
> }
>
> static inline void
> register_address_increment(struct x86_emulate_ctxt *ctxt, unsigned long *reg, int inc)
> {
> - ulong mask;
> -
> - if (ctxt->ad_bytes == sizeof(unsigned long))
> - mask = ~0UL;
> - else
> - mask = ad_mask(ctxt);
> - masked_increment(reg, mask, inc);
> + masked_increment(reg, ctxt->ad_bytes, inc);
> }
>
> static void rsp_increment(struct x86_emulate_ctxt *ctxt, int inc)
> {
> - masked_increment(reg_rmw(ctxt, VCPU_REGS_RSP), stack_mask(ctxt), inc);
> + masked_increment(reg_rmw(ctxt, VCPU_REGS_RSP), stack_size(ctxt), inc);
> }
>
> static inline void jmp_rel(struct x86_emulate_ctxt *ctxt, int rel)
> @@ -1712,17 +1718,17 @@ static int em_enter(struct x86_emulate_ctxt *ctxt)
> if (rc != X86EMUL_CONTINUE)
> return rc;
> assign_masked(reg_rmw(ctxt, VCPU_REGS_RBP), reg_read(ctxt, VCPU_REGS_RSP),
> - stack_mask(ctxt));
> + stack_size(ctxt));
> assign_masked(reg_rmw(ctxt, VCPU_REGS_RSP),
> reg_read(ctxt, VCPU_REGS_RSP) - frame_size,
> - stack_mask(ctxt));
> + stack_size(ctxt));
> return X86EMUL_CONTINUE;
> }
>
> static int em_leave(struct x86_emulate_ctxt *ctxt)
> {
> assign_masked(reg_rmw(ctxt, VCPU_REGS_RSP), reg_read(ctxt, VCPU_REGS_RBP),
> - stack_mask(ctxt));
> + stack_size(ctxt));
> return emulate_pop(ctxt, reg_rmw(ctxt, VCPU_REGS_RBP), ctxt->op_bytes);
> }
>
> @@ -4570,6 +4576,8 @@ int x86_emulate_insn(struct x86_emulate_ctxt *ctxt)
> if (ctxt->rep_prefix && (ctxt->d & String)) {
> /* All REP prefixes have the same first termination condition */
> if (address_mask(ctxt, reg_read(ctxt, VCPU_REGS_RCX)) == 0) {
> + assign_masked(reg_write(ctxt, VCPU_REGS_RCX), 0,
> + ctxt->ad_bytes);
> ctxt->eip = ctxt->_eip;
> goto done;
> }
--
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