Commit a5ba67b4 authored by Sean Christopherson's avatar Sean Christopherson Committed by Paolo Bonzini
Browse files

KVM: x86: Omit VCPU_REGS_RIP from emulator's _regs array 



Omit RIP from the emulator's _regs array, which is used only for GPRs,
i.e. registers that can be referenced via ModRM and/or SIB bytes.  The
emulator uses the dedicated _eip field for RIP, and manually reads from
_eip to handle RIP-relative addressing.

To avoid an even bigger, slightly more dangerous change, hardcode the
number of GPRs to 16 for the time being even though 32-bit KVM's emulator
technically should only have 8 GPRs.  Add a TODO to address that in a
future commit.

See also the comments above the read_gpr() and write_gpr() declarations,
and obviously the handling in writeback_registers().

No functional change intended.

Signed-off-by: default avatarSean Christopherson <seanjc@google.com>
Reviewed-by: default avatarKees Cook <keescook@chromium.org>
Message-Id: <20220526210817.3428868-4-seanjc@google.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent dfe21e6b

arch/x86/kvm/emulate.c

+5 −5
Original line number Diff line number Diff line
@@ -247,8 +247,8 @@ enum x86_transfer_type { 


static ulong reg_read(struct x86_emulate_ctxt *ctxt, unsigned nr)

{

	if (WARN_ON_ONCE(nr >= 16))

		nr &= 16 - 1;

	if (WARN_ON_ONCE(nr >= NR_EMULATOR_GPRS))

		nr &= NR_EMULATOR_GPRS - 1;



	if (!(ctxt->regs_valid & (1 << nr))) {

		ctxt->regs_valid |= 1 << nr;
@@ -259,8 +259,8 @@ static ulong reg_read(struct x86_emulate_ctxt *ctxt, unsigned nr) 


static ulong *reg_write(struct x86_emulate_ctxt *ctxt, unsigned nr)

{

	if (WARN_ON_ONCE(nr >= 16))

		nr &= 16 - 1;

	if (WARN_ON_ONCE(nr >= NR_EMULATOR_GPRS))

		nr &= NR_EMULATOR_GPRS - 1;



	ctxt->regs_valid |= 1 << nr;

	ctxt->regs_dirty |= 1 << nr;
@@ -278,7 +278,7 @@ static void writeback_registers(struct x86_emulate_ctxt *ctxt) 
	unsigned long dirty = ctxt->regs_dirty;

	unsigned reg;



	for_each_set_bit(reg, &dirty, 16)

	for_each_set_bit(reg, &dirty, NR_EMULATOR_GPRS)

		ctxt->ops->write_gpr(ctxt, reg, ctxt->_regs[reg]);

}

arch/x86/kvm/kvm_emulate.h

+12 −1
Original line number Diff line number Diff line
@@ -301,6 +301,17 @@ struct fastop; 


typedef void (*fastop_t)(struct fastop *);



/*

 * The emulator's _regs array tracks only the GPRs, i.e. excludes RIP.  RIP is

 * tracked/accessed via _eip, and except for RIP relative addressing, which

 * also uses _eip, RIP cannot be a register operand nor can it be an operand in

 * a ModRM or SIB byte.

 *

 * TODO: this is technically wrong for 32-bit KVM, which only supports 8 GPRs;

 * R8-R15 don't exist.

 */

#define NR_EMULATOR_GPRS	16



struct x86_emulate_ctxt {

	void *vcpu;

	const struct x86_emulate_ops *ops;
@@ -363,7 +374,7 @@ struct x86_emulate_ctxt { 
	struct operand src2;

	struct operand dst;

	struct operand memop;

	unsigned long _regs[NR_VCPU_REGS];

	unsigned long _regs[NR_EMULATOR_GPRS];

	struct operand *memopp;

	struct fetch_cache fetch;

	struct read_cache io_read;