[PATCH v4 4/5] KVM: MMU: Add support for PKS emulation
From: Chenyi Qiang
Date: Fri Feb 05 2021 - 03:38:44 EST
In addition to the pkey check for user pages, advertise pkr_mask also to
cache the conditions where protection key checks for supervisor pages
are needed. Add CR4_PKS in mmu_role_bits to track the pkr_mask update on
a per-mmu basis.
In original cache conditions of pkr_mask, U/S bit in page tables is a
judgement condition and replace the PFEC.RSVD in page fault error code
to form the index of 16 domains. PKS support would extend the U/S bits
(if U/S=0, PKS check required). It adds an additional check for
cr4_pke/cr4_pks to ensure the necessity and distinguish PKU and PKS from
each other.
Signed-off-by: Chenyi Qiang <chenyi.qiang@xxxxxxxxx>
---
arch/x86/include/asm/kvm_host.h | 11 +++---
arch/x86/kvm/mmu.h | 13 ++++---
arch/x86/kvm/mmu/mmu.c | 63 +++++++++++++++++++--------------
arch/x86/kvm/x86.c | 3 +-
4 files changed, 53 insertions(+), 37 deletions(-)
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 1909d34cbac8..e515f1cecb88 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -294,7 +294,7 @@ union kvm_mmu_extended_role {
unsigned int cr0_pg:1;
unsigned int cr4_pae:1;
unsigned int cr4_pse:1;
- unsigned int cr4_pke:1;
+ unsigned int cr4_pkr:1;
unsigned int cr4_smap:1;
unsigned int cr4_smep:1;
unsigned int maxphyaddr:6;
@@ -378,10 +378,11 @@ struct kvm_mmu {
u8 permissions[16];
/*
- * The pkru_mask indicates if protection key checks are needed. It
- * consists of 16 domains indexed by page fault error code bits [4:1],
- * with PFEC.RSVD replaced by ACC_USER_MASK from the page tables.
- * Each domain has 2 bits which are ANDed with AD and WD from PKRU.
+ * The pkr_mask indicates if protection key checks are needed.
+ * It consists of 16 domains indexed by page fault error code
+ * bits[4:1] with PFEC.RSVD replaced by ACC_USER_MASK from the
+ * page tables. Each domain has 2 bits which are ANDed with AD
+ * and WD from PKRU/PKRS.
*/
u32 pkr_mask;
diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
index a77bd20c83f9..55b71c28e46e 100644
--- a/arch/x86/kvm/mmu.h
+++ b/arch/x86/kvm/mmu.h
@@ -192,14 +192,17 @@ static inline u8 permission_fault(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu,
WARN_ON(pfec & (PFERR_PK_MASK | PFERR_RSVD_MASK));
if (unlikely(mmu->pkr_mask)) {
u32 pkr_bits, offset;
+ u64 pkr;
/*
- * PKRU defines 32 bits, there are 16 domains and 2
- * attribute bits per domain in pkru. pte_pkey is the
- * index of the protection domain, so pte_pkey * 2 is
- * is the index of the first bit for the domain.
+ * PKRU and PKRS both define 32 bits. There are 16 domains
+ * and 2 attribute bits per domain in them. pte_key is the
+ * index of the protection domain, so pte_pkey * 2 is the
+ * index of the first bit for the domain. The choice of
+ * PKRU and PKRS is determined by the accessed pages.
*/
- pkr_bits = (vcpu->arch.pkru >> (pte_pkey * 2)) & 3;
+ pkr = pte_access & PT_USER_MASK ? vcpu->arch.pkru : vcpu->arch.pkrs;
+ pkr_bits = (pkr >> pte_pkey * 2) & 3;
/* clear present bit, replace PFEC.RSVD with ACC_USER_MASK. */
offset = (pfec & ~1) +
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index d22c0813e4b9..92b24fa71f93 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -4278,42 +4278,49 @@ static void update_permission_bitmask(struct kvm_vcpu *vcpu,
}
/*
-* PKU is an additional mechanism by which the paging controls access to
-* user-mode addresses based on the value in the PKRU register. Protection
-* key violations are reported through a bit in the page fault error code.
+* Protection Keys (PKEY) is an additional mechanism by which
+* the paging controls access to user-mode/supervisor-mode address
+* based on the values in PKEY registers (PKRU/PKRS). Protection key
+* violations are reported through a bit in the page fault error code.
* Unlike other bits of the error code, the PK bit is not known at the
* call site of e.g. gva_to_gpa; it must be computed directly in
-* permission_fault based on two bits of PKRU, on some machine state (CR4,
-* CR0, EFER, CPL), and on other bits of the error code and the page tables.
+* permission_fault based on two bits of PKRU/PKRS, on some machine
+* state (CR4, CR0, EFER, CPL), and on other bits of the error code
+* and the page tables.
*
* In particular the following conditions come from the error code, the
* page tables and the machine state:
-* - PK is always zero unless CR4.PKE=1 and EFER.LMA=1
+* - PK is always zero unless CR4.PKE=1/CR4.PKS=1 and EFER.LMA=1
* - PK is always zero if RSVD=1 (reserved bit set) or F=1 (instruction fetch)
-* - PK is always zero if U=0 in the page tables
-* - PKRU.WD is ignored if CR0.WP=0 and the access is a supervisor access.
+* - PK is always zero if
+* - U=0 in the page tables and CR4.PKS=0
+* - U=1 in the page tables and CR4.PKU=0
+* - (PKRU/PKRS).WD is ignored if CR0.WP=0 and the access is a supervisor access.
*
-* The PKRU bitmask caches the result of these four conditions. The error
-* code (minus the P bit) and the page table's U bit form an index into the
-* PKRU bitmask. Two bits of the PKRU bitmask are then extracted and ANDed
-* with the two bits of the PKRU register corresponding to the protection key.
-* For the first three conditions above the bits will be 00, thus masking
-* away both AD and WD. For all reads or if the last condition holds, WD
-* only will be masked away.
+* The pkr_mask caches the result of these three conditions. The error
+* code (minus the P bit) and the page table's U bit form an index into
+* the pkr_mask. Two bits of the pkr_mask are then extracted and ANDed with
+* the two bits of the PKEY register corresponding to the protection key.
+* For the first three conditions above the bits will be 00, thus masking away
+* both AD and WD. For all reads or if the last condition holds, WD only will be
+* masked away.
*/
static void update_pkr_bitmask(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu,
bool ept)
{
unsigned bit;
- bool wp;
+ bool wp, cr4_pke, cr4_pks;
if (ept) {
mmu->pkr_mask = 0;
return;
}
- /* PKEY is enabled only if CR4.PKE and EFER.LMA are both set. */
- if (!kvm_read_cr4_bits(vcpu, X86_CR4_PKE) || !is_long_mode(vcpu)) {
+ cr4_pke = kvm_read_cr4_bits(vcpu, X86_CR4_PKE) != 0;
+ cr4_pks = kvm_read_cr4_bits(vcpu, X86_CR4_PKS) != 0;
+
+ /* PKEY is enabled only if CR4.PKE/CR4.PKS and EFER.LMA are both set. */
+ if ((!cr4_pke && !cr4_pks) || !is_long_mode(vcpu)) {
mmu->pkr_mask = 0;
return;
}
@@ -4333,19 +4340,22 @@ static void update_pkr_bitmask(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu,
pte_user = pfec & PFERR_RSVD_MASK;
/*
- * Only need to check the access which is not an
- * instruction fetch and is to a user page.
+ * need to check the access which is not an
+ * instruction fetch and
+ * - if cr4_pke 1-setting when accessing a user page.
+ * - if cr4_pks 1-setting when accessing a supervisor page.
*/
- check_pkey = (!ff && pte_user);
+ check_pkey = !ff && (pte_user ? cr4_pke : cr4_pks);
+
/*
- * write access is controlled by PKRU if it is a
- * user access or CR0.WP = 1.
+ * write access is controlled by PKRU/PKRS if
+ * it is a user access or CR0.WP = 1.
*/
check_write = check_pkey && wf && (uf || wp);
- /* PKRU.AD stops both read and write access. */
+ /* PKRU/PKRS.AD stops both read and write access. */
pkey_bits = !!check_pkey;
- /* PKRU.WD stops write access. */
+ /* PKRU/PKRS.WD stops write access. */
pkey_bits |= (!!check_write) << 1;
mmu->pkr_mask |= (pkey_bits & 3) << pfec;
@@ -4427,7 +4437,8 @@ static union kvm_mmu_extended_role kvm_calc_mmu_role_ext(struct kvm_vcpu *vcpu)
ext.cr4_smep = !!kvm_read_cr4_bits(vcpu, X86_CR4_SMEP);
ext.cr4_smap = !!kvm_read_cr4_bits(vcpu, X86_CR4_SMAP);
ext.cr4_pse = !!is_pse(vcpu);
- ext.cr4_pke = !!kvm_read_cr4_bits(vcpu, X86_CR4_PKE);
+ ext.cr4_pkr = !!kvm_read_cr4_bits(vcpu, X86_CR4_PKE) ||
+ !!kvm_read_cr4_bits(vcpu, X86_CR4_PKS);
ext.maxphyaddr = cpuid_maxphyaddr(vcpu);
ext.valid = 1;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 684ef760481c..aec889a4eb66 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -982,7 +982,8 @@ int kvm_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
unsigned long old_cr4 = kvm_read_cr4(vcpu);
unsigned long pdptr_bits = X86_CR4_PGE | X86_CR4_PSE | X86_CR4_PAE |
X86_CR4_SMEP;
- unsigned long mmu_role_bits = pdptr_bits | X86_CR4_SMAP | X86_CR4_PKE;
+ unsigned long mmu_role_bits = pdptr_bits | X86_CR4_SMAP | X86_CR4_PKE |
+ X86_CR4_PKS;
if (kvm_valid_cr4(vcpu, cr4))
return 1;
--
2.17.1