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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
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13
arch/x86/kvm/kvm_emulate.h
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@ -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;