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KVM: arm64: Extend masking facility to arbitrary registers

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We currently only use the masking (RES0/RES1) facility for VNCR
registers, as they are memory-based and thus easy to sanitise.

But we could apply the same thing to other registers if we:

- split the sanitisation from __VNCR_START__
- apply the sanitisation when reading from a HW register

This involves a new "marker" in the vcpu_sysreg enum, which
defines the point at which the sanitisation applies (the VNCR
registers being of course after this marker).

Whle we are at it, rename kvm_vcpu_sanitise_vncr_reg() to
kvm_vcpu_apply_reg_masks(), which is vaguely more explicit,
and harden set_sysreg_masks() against setting masks for
random registers...

Signed-off-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Joey Gouly <joey.gouly@arm.com>
Link: https://lore.kernel.org/r/20241023145345.1613824-10-maz@kernel.org
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
This commit is contained in:
Marc Zyngier 2024-10-23 15:53:17 +01:00 • committed by Oliver Upton
parent 14ca930d82
commit a016202009
3 changed files with 24 additions and 10 deletions
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19
arch/arm64/include/asm/kvm_host.h
View file

@ -374,7 +374,7 @@ struct kvm_arch {
u64 ctr_el0;
/* Masks for VNCR-baked sysregs */
/* Masks for VNCR-backed and general EL2 sysregs */
struct kvm_sysreg_masks *sysreg_masks;
/*
@ -408,6 +408,9 @@ struct kvm_vcpu_fault_info {
r = __VNCR_START__ + ((VNCR_ ## r) / 8), \
__after_##r = __MAX__(__before_##r - 1, r)
#define MARKER(m) \
m, __after_##m = m - 1
enum vcpu_sysreg {
__INVALID_SYSREG__, /* 0 is reserved as an invalid value */
MPIDR_EL1, /* MultiProcessor Affinity Register */
@ -494,7 +497,11 @@ enum vcpu_sysreg {
CNTHV_CTL_EL2,
CNTHV_CVAL_EL2,
__VNCR_START__, /* Any VNCR-capable reg goes after this point */
/* Anything from this can be RES0/RES1 sanitised */
MARKER(__SANITISED_REG_START__),
/* Any VNCR-capable reg goes after this point */
MARKER(__VNCR_START__),
VNCR(SCTLR_EL1),/* System Control Register */
VNCR(ACTLR_EL1),/* Auxiliary Control Register */
@ -554,7 +561,7 @@ struct kvm_sysreg_masks {
struct {
u64 res0;
u64 res1;
} mask[NR_SYS_REGS - __VNCR_START__];
} mask[NR_SYS_REGS - __SANITISED_REG_START__];
};
struct kvm_cpu_context {
@ -1002,13 +1009,13 @@ static inline u64 *___ctxt_sys_reg(const struct kvm_cpu_context *ctxt, int r)
#define ctxt_sys_reg(c,r) (*__ctxt_sys_reg(c,r))
u64 kvm_vcpu_sanitise_vncr_reg(const struct kvm_vcpu *, enum vcpu_sysreg);
u64 kvm_vcpu_apply_reg_masks(const struct kvm_vcpu *, enum vcpu_sysreg, u64);
#define __vcpu_sys_reg(v,r) \
(*({ \
const struct kvm_cpu_context *ctxt = &(v)->arch.ctxt; \
u64 *__r = __ctxt_sys_reg(ctxt, (r)); \
if (vcpu_has_nv((v)) && (r) >= __VNCR_START__) \
*__r = kvm_vcpu_sanitise_vncr_reg((v), (r)); \
if (vcpu_has_nv((v)) && (r) >= __SANITISED_REG_START__) \
*__r = kvm_vcpu_apply_reg_masks((v), (r), *__r);\
__r; \
}))

12
arch/arm64/kvm/nested.c
View file

@ -933,15 +933,15 @@ static void limit_nv_id_regs(struct kvm *kvm)
kvm_set_vm_id_reg(kvm, SYS_ID_AA64DFR0_EL1, val);
}
u64 kvm_vcpu_sanitise_vncr_reg(const struct kvm_vcpu *vcpu, enum vcpu_sysreg sr)
u64 kvm_vcpu_apply_reg_masks(const struct kvm_vcpu *vcpu,
enum vcpu_sysreg sr, u64 v)
{
u64 v = ctxt_sys_reg(&vcpu->arch.ctxt, sr);
struct kvm_sysreg_masks *masks;
masks = vcpu->kvm->arch.sysreg_masks;
if (masks) {
sr -= __VNCR_START__;
sr -= __SANITISED_REG_START__;
v &= ~masks->mask[sr].res0;
v |= masks->mask[sr].res1;
@ -952,7 +952,11 @@ u64 kvm_vcpu_sanitise_vncr_reg(const struct kvm_vcpu *vcpu, enum vcpu_sysreg sr)
static void set_sysreg_masks(struct kvm *kvm, int sr, u64 res0, u64 res1)
{
int i = sr - __VNCR_START__;
int i = sr - __SANITISED_REG_START__;
BUILD_BUG_ON(!__builtin_constant_p(sr));
BUILD_BUG_ON(sr < __SANITISED_REG_START__);
BUILD_BUG_ON(sr >= NR_SYS_REGS);
kvm->arch.sysreg_masks->mask[i].res0 = res0;
kvm->arch.sysreg_masks->mask[i].res1 = res1;

3
arch/arm64/kvm/sys_regs.c
View file

@ -189,6 +189,9 @@ u64 vcpu_read_sys_reg(const struct kvm_vcpu *vcpu, int reg)
/* Get the current version of the EL1 counterpart. */
WARN_ON(!__vcpu_read_sys_reg_from_cpu(el1r, &val));
if (reg >= __SANITISED_REG_START__)
val = kvm_vcpu_apply_reg_masks(vcpu, reg, val);
return val;
}