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

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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: Sean Christopherson <seanjc@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Message-Id: <20220526210817.3428868-4-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Sean Christopherson
2022-05-26 21:08:12 +00:00
committed by Paolo Bonzini
parent dfe21e6bc0
commit a5ba67b42f
2 changed files with 17 additions and 6 deletions
Download Patch File Download Diff File Expand all files Collapse all files

10
arch/x86/kvm/emulate.c
View File

@ -247,8 +247,8 @@ enum x86_transfer_type {
static ulong reg_read(struct x86_emulate_ctxt *ctxt, unsigned nr) static ulong reg_read(struct x86_emulate_ctxt *ctxt, unsigned nr)
{ {
if (WARN_ON_ONCE(nr >= 16)) if (WARN_ON_ONCE(nr >= NR_EMULATOR_GPRS))
nr &= 16 - 1; nr &= NR_EMULATOR_GPRS - 1;
if (!(ctxt->regs_valid & (1 << nr))) { if (!(ctxt->regs_valid & (1 << nr))) {
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) static ulong *reg_write(struct x86_emulate_ctxt *ctxt, unsigned nr)
{ {
if (WARN_ON_ONCE(nr >= 16)) if (WARN_ON_ONCE(nr >= NR_EMULATOR_GPRS))
nr &= 16 - 1; nr &= NR_EMULATOR_GPRS - 1;
ctxt->regs_valid |= 1 << nr; ctxt->regs_valid |= 1 << nr;
ctxt->regs_dirty |= 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 long dirty = ctxt->regs_dirty;
unsigned reg; 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]); ctxt->ops->write_gpr(ctxt, reg, ctxt->_regs[reg]);
} }

13
arch/x86/kvm/kvm_emulate.h
View File

@ -301,6 +301,17 @@ struct fastop;
typedef void (*fastop_t)(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 { struct x86_emulate_ctxt {
void *vcpu; void *vcpu;
const struct x86_emulate_ops *ops; const struct x86_emulate_ops *ops;
@ -363,7 +374,7 @@ struct x86_emulate_ctxt {
struct operand src2; struct operand src2;
struct operand dst; struct operand dst;
struct operand memop; struct operand memop;
unsigned long _regs[NR_VCPU_REGS]; unsigned long _regs[NR_EMULATOR_GPRS];
struct operand *memopp; struct operand *memopp;
struct fetch_cache fetch; struct fetch_cache fetch;
struct read_cache io_read; struct read_cache io_read;